From b247a7b843051ff60867eee79a340a0b3e1a3b45 Mon Sep 17 00:00:00 2001
From: sayantn <sayantn05@gmail.com>
Date: Fri, 30 May 2025 19:56:18 +0530
Subject: [PATCH 1/7] Codegen **non-overloaded** LLVM intrinsics using their
 name

---
 compiler/rustc_codegen_gcc/src/type_of.rs     |   8 +-
 compiler/rustc_codegen_llvm/src/abi.rs        | 157 +++++++++++++++---
 compiler/rustc_codegen_llvm/src/builder.rs    |   6 +-
 compiler/rustc_codegen_llvm/src/declare.rs    |  41 +++--
 compiler/rustc_codegen_llvm/src/intrinsic.rs  |   2 +-
 .../rustc_codegen_llvm/src/llvm/enzyme_ffi.rs |   1 -
 compiler/rustc_codegen_llvm/src/llvm/ffi.rs   |   9 +
 compiler/rustc_codegen_llvm/src/llvm/mod.rs   |   8 +
 compiler/rustc_codegen_llvm/src/type_.rs      |  16 +-
 compiler/rustc_codegen_ssa/src/mir/block.rs   |   4 +-
 compiler/rustc_codegen_ssa/src/mir/rvalue.rs  |   2 +-
 compiler/rustc_codegen_ssa/src/size_of_val.rs |   2 +-
 .../rustc_codegen_ssa/src/traits/type_.rs     |   6 +-
 13 files changed, 216 insertions(+), 46 deletions(-)

diff --git a/compiler/rustc_codegen_gcc/src/type_of.rs b/compiler/rustc_codegen_gcc/src/type_of.rs
index 93202483eed81..1983941c657f6 100644
--- a/compiler/rustc_codegen_gcc/src/type_of.rs
+++ b/compiler/rustc_codegen_gcc/src/type_of.rs
@@ -1,6 +1,6 @@
 use std::fmt::Write;
 
-use gccjit::{Struct, Type};
+use gccjit::{RValue, Struct, Type};
 use rustc_abi as abi;
 use rustc_abi::Primitive::*;
 use rustc_abi::{
@@ -373,7 +373,11 @@ impl<'gcc, 'tcx> LayoutTypeCodegenMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         unimplemented!();
     }
 
-    fn fn_decl_backend_type(&self, fn_abi: &FnAbi<'tcx, Ty<'tcx>>) -> Type<'gcc> {
+    fn fn_decl_backend_type(
+        &self,
+        fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
+        _fn_ptr: RValue<'gcc>,
+    ) -> Type<'gcc> {
         // FIXME(antoyo): Should we do something with `FnAbiGcc::fn_attributes`?
         let FnAbiGcc { return_type, arguments_type, is_c_variadic, .. } = fn_abi.gcc_type(self);
         self.context.new_function_pointer_type(None, return_type, &arguments_type, is_c_variadic)
diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index 680ad98593e7e..abfa3315b12fd 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -1,4 +1,5 @@
-use std::cmp;
+use std::borrow::Borrow;
+use std::{cmp, iter};
 
 use libc::c_uint;
 use rustc_abi::{
@@ -301,8 +302,37 @@ impl<'ll, 'tcx> ArgAbiBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
     }
 }
 
+pub(crate) enum FunctionSignature<'ll> {
+    /// The signature is obtained directly from LLVM, and **may not match the Rust signature**
+    Intrinsic(&'ll Type),
+    /// The name starts with `llvm.`, but can't obtain the intrinsic ID. May be invalid or upgradable
+    MaybeInvalidIntrinsic(&'ll Type),
+    /// Just the Rust signature
+    Rust(&'ll Type),
+}
+
+impl<'ll> FunctionSignature<'ll> {
+    pub(crate) fn fn_ty(&self) -> &'ll Type {
+        match self {
+            FunctionSignature::Intrinsic(fn_ty)
+            | FunctionSignature::MaybeInvalidIntrinsic(fn_ty)
+            | FunctionSignature::Rust(fn_ty) => fn_ty,
+        }
+    }
+}
+
 pub(crate) trait FnAbiLlvmExt<'ll, 'tcx> {
-    fn llvm_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type;
+    fn llvm_return_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type;
+    fn llvm_argument_types(&self, cx: &CodegenCx<'ll, 'tcx>) -> Vec<&'ll Type>;
+    fn llvm_type(
+        &self,
+        cx: &CodegenCx<'ll, 'tcx>,
+        name: &[u8],
+        do_verify: bool,
+    ) -> FunctionSignature<'ll>;
+    /// **If this function is an LLVM intrinsic** checks if the LLVM signature provided matches with this
+    fn verify_intrinsic_signature(&self, cx: &CodegenCx<'ll, 'tcx>, llvm_ty: &'ll Type) -> bool;
+
     fn ptr_to_llvm_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type;
     fn llvm_cconv(&self, cx: &CodegenCx<'ll, 'tcx>) -> llvm::CallConv;
 
@@ -315,30 +345,39 @@ pub(crate) trait FnAbiLlvmExt<'ll, 'tcx> {
     );
 
     /// Apply attributes to a function call.
-    fn apply_attrs_callsite(&self, bx: &mut Builder<'_, 'll, 'tcx>, callsite: &'ll Value);
+    fn apply_attrs_callsite(
+        &self,
+        bx: &mut Builder<'_, 'll, 'tcx>,
+        callsite: &'ll Value,
+        llfn: &'ll Value,
+    );
 }
 
 impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
-    fn llvm_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type {
+    fn llvm_return_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type {
+        match &self.ret.mode {
+            PassMode::Ignore => cx.type_void(),
+            PassMode::Direct(_) | PassMode::Pair(..) => self.ret.layout.immediate_llvm_type(cx),
+            PassMode::Cast { cast, pad_i32: _ } => cast.llvm_type(cx),
+            PassMode::Indirect { .. } => cx.type_void(),
+        }
+    }
+
+    fn llvm_argument_types(&self, cx: &CodegenCx<'ll, 'tcx>) -> Vec<&'ll Type> {
+        let indirect_return = matches!(self.ret.mode, PassMode::Indirect { .. });
+
         // Ignore "extra" args from the call site for C variadic functions.
         // Only the "fixed" args are part of the LLVM function signature.
         let args =
             if self.c_variadic { &self.args[..self.fixed_count as usize] } else { &self.args };
 
         // This capacity calculation is approximate.
-        let mut llargument_tys = Vec::with_capacity(
-            self.args.len() + if let PassMode::Indirect { .. } = self.ret.mode { 1 } else { 0 },
-        );
+        let mut llargument_tys =
+            Vec::with_capacity(args.len() + if indirect_return { 1 } else { 0 });
 
-        let llreturn_ty = match &self.ret.mode {
-            PassMode::Ignore => cx.type_void(),
-            PassMode::Direct(_) | PassMode::Pair(..) => self.ret.layout.immediate_llvm_type(cx),
-            PassMode::Cast { cast, pad_i32: _ } => cast.llvm_type(cx),
-            PassMode::Indirect { .. } => {
-                llargument_tys.push(cx.type_ptr());
-                cx.type_void()
-            }
-        };
+        if indirect_return {
+            llargument_tys.push(cx.type_ptr());
+        }
 
         for arg in args {
             // Note that the exact number of arguments pushed here is carefully synchronized with
@@ -385,10 +424,72 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             llargument_tys.push(llarg_ty);
         }
 
-        if self.c_variadic {
-            cx.type_variadic_func(&llargument_tys, llreturn_ty)
+        llargument_tys
+    }
+
+    fn verify_intrinsic_signature(&self, cx: &CodegenCx<'ll, 'tcx>, llvm_fn_ty: &'ll Type) -> bool {
+        let rust_return_ty = self.llvm_return_type(cx);
+        let rust_argument_tys = self.llvm_argument_types(cx);
+
+        let llvm_return_ty = cx.get_return_type(llvm_fn_ty);
+        let llvm_argument_tys = cx.func_params_types(llvm_fn_ty);
+        let llvm_is_variadic = cx.func_is_variadic(llvm_fn_ty);
+
+        if self.c_variadic != llvm_is_variadic || rust_argument_tys.len() != llvm_argument_tys.len()
+        {
+            return false;
+        }
+
+        iter::once((rust_return_ty, llvm_return_ty))
+            .chain(iter::zip(rust_argument_tys, llvm_argument_tys))
+            .all(|(rust_ty, llvm_ty)| rust_ty == llvm_ty)
+    }
+
+    fn llvm_type(
+        &self,
+        cx: &CodegenCx<'ll, 'tcx>,
+        name: &[u8],
+        do_verify: bool,
+    ) -> FunctionSignature<'ll> {
+        let mut maybe_invalid = false;
+
+        if name.starts_with(b"llvm.") {
+            if let Some(intrinsic) = llvm::Intrinsic::lookup(name) {
+                if !intrinsic.is_overloaded() {
+                    // FIXME: also do this for overloaded intrinsics
+                    let llvm_fn_ty = intrinsic.get_type(cx.llcx, &[]);
+                    if do_verify {
+                        if !self.verify_intrinsic_signature(cx, llvm_fn_ty) {
+                            cx.tcx.dcx().fatal(format!(
+                                "Intrinsic signature mismatch for `{}`: expected signature `{llvm_fn_ty:?}`",
+                                str::from_utf8(name).unwrap()
+                            ));
+                        }
+                    }
+                    return FunctionSignature::Intrinsic(llvm_fn_ty);
+                }
+            } else {
+                // it's one of 2 cases,
+                // - either the base name is invalid
+                // - it has been superseded by something else, so the intrinsic was removed entirely
+                // to check for upgrades, we need the `llfn`, so we defer it for now
+                maybe_invalid = true;
+            }
+        }
+
+        let return_ty = self.llvm_return_type(cx);
+        let argument_tys = self.llvm_argument_types(cx);
+
+        let fn_ty = if self.c_variadic {
+            cx.type_variadic_func(&argument_tys, return_ty)
         } else {
-            cx.type_func(&llargument_tys, llreturn_ty)
+            cx.type_func(&argument_tys, return_ty)
+        };
+
+        if maybe_invalid {
+            FunctionSignature::MaybeInvalidIntrinsic(fn_ty)
+        } else {
+            FunctionSignature::Rust(fn_ty)
         }
     }
 
@@ -546,7 +647,23 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         }
     }
 
-    fn apply_attrs_callsite(&self, bx: &mut Builder<'_, 'll, 'tcx>, callsite: &'ll Value) {
+    fn apply_attrs_callsite(
+        &self,
+        bx: &mut Builder<'_, 'll, 'tcx>,
+        callsite: &'ll Value,
+        llfn: &'ll Value,
+    ) {
+        // if we are using the LLVM signature, use the LLVM attributes otherwise it might be problematic
+        let name = llvm::get_value_name(llfn);
+        if name.starts_with(b"llvm.")
+            && let Some(intrinsic) = llvm::Intrinsic::lookup(&name)
+        {
+            // FIXME: also do this for overloaded intrinsics
+            if !intrinsic.is_overloaded() {
+                return;
+            }
+        }
+
         let mut func_attrs = SmallVec::<[_; 2]>::new();
         if self.ret.layout.is_uninhabited() {
             func_attrs.push(llvm::AttributeKind::NoReturn.create_attr(bx.cx.llcx));
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index e65f3d292dbb8..c4ad0395f2631 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -443,7 +443,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
             )
         };
         if let Some(fn_abi) = fn_abi {
-            fn_abi.apply_attrs_callsite(self, invoke);
+            fn_abi.apply_attrs_callsite(self, invoke, llfn);
         }
         invoke
     }
@@ -1445,7 +1445,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         }
 
         if let Some(fn_abi) = fn_abi {
-            fn_abi.apply_attrs_callsite(self, call);
+            fn_abi.apply_attrs_callsite(self, call, llfn);
         }
         call
     }
@@ -1785,7 +1785,7 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
             )
         };
         if let Some(fn_abi) = fn_abi {
-            fn_abi.apply_attrs_callsite(self, callbr);
+            fn_abi.apply_attrs_callsite(self, callbr, llfn);
         }
         callbr
     }
diff --git a/compiler/rustc_codegen_llvm/src/declare.rs b/compiler/rustc_codegen_llvm/src/declare.rs
index 48b2d09afb674..73350e691d1f4 100644
--- a/compiler/rustc_codegen_llvm/src/declare.rs
+++ b/compiler/rustc_codegen_llvm/src/declare.rs
@@ -22,7 +22,7 @@ use rustc_target::callconv::FnAbi;
 use smallvec::SmallVec;
 use tracing::debug;
 
-use crate::abi::FnAbiLlvmExt;
+use crate::abi::{FnAbiLlvmExt, FunctionSignature};
 use crate::attributes;
 use crate::common::AsCCharPtr;
 use crate::context::{CodegenCx, GenericCx, SCx, SimpleCx};
@@ -148,17 +148,34 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
     ) -> &'ll Value {
         debug!("declare_rust_fn(name={:?}, fn_abi={:?})", name, fn_abi);
 
-        // Function addresses in Rust are never significant, allowing functions to
-        // be merged.
-        let llfn = declare_raw_fn(
-            self,
-            name,
-            fn_abi.llvm_cconv(self),
-            llvm::UnnamedAddr::Global,
-            llvm::Visibility::Default,
-            fn_abi.llvm_type(self),
-        );
-        fn_abi.apply_attrs_llfn(self, llfn, instance);
+        let signature = fn_abi.llvm_type(self, name.as_bytes(), true);
+        let llfn;
+
+        if let FunctionSignature::Intrinsic(fn_ty) = signature {
+            // intrinsics have a specified set of attributes, so we don't use the `FnAbi` set for them
+            llfn = declare_simple_fn(
+                self,
+                name,
+                fn_abi.llvm_cconv(self),
+                llvm::UnnamedAddr::Global,
+                llvm::Visibility::Default,
+                fn_ty,
+            );
+        } else {
+            // Function addresses in Rust are never significant, allowing functions to
+            // be merged.
+            llfn = declare_raw_fn(
+                self,
+                name,
+                fn_abi.llvm_cconv(self),
+                llvm::UnnamedAddr::Global,
+                llvm::Visibility::Default,
+                signature.fn_ty(),
+            );
+            fn_abi.apply_attrs_llfn(self, llfn, instance);
+        }
+
+        // todo: check for upgrades, and emit error if not upgradable
 
         if self.tcx.sess.is_sanitizer_cfi_enabled() {
             if let Some(instance) = instance {
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index c12383f19312d..da5f5a9afb909 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -1073,7 +1073,7 @@ fn gen_fn<'a, 'll, 'tcx>(
     codegen: &mut dyn FnMut(Builder<'a, 'll, 'tcx>),
 ) -> (&'ll Type, &'ll Value) {
     let fn_abi = cx.fn_abi_of_fn_ptr(rust_fn_sig, ty::List::empty());
-    let llty = fn_abi.llvm_type(cx);
+    let llty = fn_abi.llvm_type(cx, name.as_bytes(), true).fn_ty();
     let llfn = cx.declare_fn(name, fn_abi, None);
     cx.set_frame_pointer_type(llfn);
     cx.apply_target_cpu_attr(llfn);
diff --git a/compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs
index e63043b21227f..496639bb8b6f4 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/enzyme_ffi.rs
@@ -73,7 +73,6 @@ unsafe extern "C" {
     pub(crate) fn LLVMDumpModule(M: &Module);
     pub(crate) fn LLVMDumpValue(V: &Value);
     pub(crate) fn LLVMGetFunctionCallConv(F: &Value) -> c_uint;
-    pub(crate) fn LLVMGetReturnType(T: &Type) -> &Type;
     pub(crate) fn LLVMGetParams(Fnc: &Value, params: *mut &Value);
     pub(crate) fn LLVMGetNamedFunction(M: &Module, Name: *const c_char) -> Option<&Value>;
 }
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index c4b5cf413a725..25556b6874ad7 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -972,6 +972,8 @@ unsafe extern "C" {
     ) -> &'a Type;
     pub(crate) fn LLVMCountParamTypes(FunctionTy: &Type) -> c_uint;
     pub(crate) fn LLVMGetParamTypes<'a>(FunctionTy: &'a Type, Dest: *mut &'a Type);
+    pub(crate) fn LLVMGetReturnType(FunctionTy: &Type) -> &Type;
+    pub(crate) fn LLVMIsFunctionVarArg(FunctionTy: &Type) -> Bool;
 
     // Operations on struct types
     pub(crate) fn LLVMStructTypeInContext<'a>(
@@ -1119,6 +1121,13 @@ unsafe extern "C" {
 
     // Operations about llvm intrinsics
     pub(crate) fn LLVMLookupIntrinsicID(Name: *const c_char, NameLen: size_t) -> c_uint;
+    pub(crate) fn LLVMIntrinsicIsOverloaded(ID: NonZero<c_uint>) -> Bool;
+    pub(crate) fn LLVMIntrinsicGetType<'a>(
+        C: &'a Context,
+        ID: NonZero<c_uint>,
+        ParamTypes: *const &'a Type,
+        ParamCount: size_t,
+    ) -> &'a Type;
     pub(crate) fn LLVMGetIntrinsicDeclaration<'a>(
         Mod: &'a Module,
         ID: NonZero<c_uint>,
diff --git a/compiler/rustc_codegen_llvm/src/llvm/mod.rs b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
index 4c58a92106d5c..aa7111474faa5 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
@@ -311,6 +311,14 @@ impl Intrinsic {
         NonZero::new(id).map(|id| Self { id })
     }
 
+    pub(crate) fn is_overloaded(self) -> bool {
+        unsafe { LLVMIntrinsicIsOverloaded(self.id).is_true() }
+    }
+
+    pub(crate) fn get_type<'ll>(self, llcx: &'ll Context, type_params: &[&'ll Type]) -> &'ll Type {
+        unsafe { LLVMIntrinsicGetType(llcx, self.id, type_params.as_ptr(), type_params.len()) }
+    }
+
     pub(crate) fn get_declaration<'ll>(
         self,
         llmod: &'ll Module,
diff --git a/compiler/rustc_codegen_llvm/src/type_.rs b/compiler/rustc_codegen_llvm/src/type_.rs
index 81bb70c958790..44d0268b7a9ef 100644
--- a/compiler/rustc_codegen_llvm/src/type_.rs
+++ b/compiler/rustc_codegen_llvm/src/type_.rs
@@ -68,6 +68,10 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
         unsafe { llvm::LLVMVectorType(ty, len as c_uint) }
     }
 
+    pub(crate) fn get_return_type(&self, ty: &'ll Type) -> &'ll Type {
+        unsafe { llvm::LLVMGetReturnType(ty) }
+    }
+
     pub(crate) fn func_params_types(&self, ty: &'ll Type) -> Vec<&'ll Type> {
         unsafe {
             let n_args = llvm::LLVMCountParamTypes(ty) as usize;
@@ -77,6 +81,10 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
             args
         }
     }
+
+    pub(crate) fn func_is_variadic(&self, ty: &'ll Type) -> bool {
+        unsafe { llvm::LLVMIsFunctionVarArg(ty).is_true() }
+    }
 }
 impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
     pub(crate) fn type_bool(&self) -> &'ll Type {
@@ -286,8 +294,12 @@ impl<'ll, 'tcx> LayoutTypeCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
     fn cast_backend_type(&self, ty: &CastTarget) -> &'ll Type {
         ty.llvm_type(self)
     }
-    fn fn_decl_backend_type(&self, fn_abi: &FnAbi<'tcx, Ty<'tcx>>) -> &'ll Type {
-        fn_abi.llvm_type(self)
+    fn fn_decl_backend_type(
+        &self,
+        fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
+        fn_ptr: &'ll Value,
+    ) -> &'ll Type {
+        fn_abi.llvm_type(self, &llvm::get_value_name(fn_ptr), false).fn_ty()
     }
     fn fn_ptr_backend_type(&self, fn_abi: &FnAbi<'tcx, Ty<'tcx>>) -> &'ll Type {
         fn_abi.ptr_to_llvm_type(self)
diff --git a/compiler/rustc_codegen_ssa/src/mir/block.rs b/compiler/rustc_codegen_ssa/src/mir/block.rs
index e371f1a76231c..ecce2d2a705e5 100644
--- a/compiler/rustc_codegen_ssa/src/mir/block.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/block.rs
@@ -197,7 +197,7 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
 
         // If there is a cleanup block and the function we're calling can unwind, then
         // do an invoke, otherwise do a call.
-        let fn_ty = bx.fn_decl_backend_type(fn_abi);
+        let fn_ty = bx.fn_decl_backend_type(fn_abi, fn_ptr);
 
         let fn_attrs = if bx.tcx().def_kind(fx.instance.def_id()).has_codegen_attrs() {
             Some(bx.tcx().codegen_fn_attrs(fx.instance.def_id()))
@@ -1846,7 +1846,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         if is_call_from_compiler_builtins_to_upstream_monomorphization(bx.tcx(), instance) {
             bx.abort();
         } else {
-            let fn_ty = bx.fn_decl_backend_type(fn_abi);
+            let fn_ty = bx.fn_decl_backend_type(fn_abi, fn_ptr);
 
             let llret = bx.call(fn_ty, None, Some(fn_abi), fn_ptr, &[], funclet.as_ref(), None);
             bx.apply_attrs_to_cleanup_callsite(llret);
diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index d629003bff5e8..20992464ae3ab 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -658,7 +658,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     };
                     let fn_ptr = bx.get_fn_addr(instance);
                     let fn_abi = bx.fn_abi_of_instance(instance, ty::List::empty());
-                    let fn_ty = bx.fn_decl_backend_type(fn_abi);
+                    let fn_ty = bx.fn_decl_backend_type(fn_abi, fn_ptr);
                     let fn_attrs = if bx.tcx().def_kind(instance.def_id()).has_codegen_attrs() {
                         Some(bx.tcx().codegen_instance_attrs(instance.def))
                     } else {
diff --git a/compiler/rustc_codegen_ssa/src/size_of_val.rs b/compiler/rustc_codegen_ssa/src/size_of_val.rs
index e1bd8014d7a2f..adebb297bd0ba 100644
--- a/compiler/rustc_codegen_ssa/src/size_of_val.rs
+++ b/compiler/rustc_codegen_ssa/src/size_of_val.rs
@@ -68,7 +68,7 @@ pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
             // Generate the call. Cannot use `do_call` since we don't have a MIR terminator so we
             // can't create a `TerminationCodegenHelper`. (But we are in good company, this code is
             // duplicated plenty of times.)
-            let fn_ty = bx.fn_decl_backend_type(fn_abi);
+            let fn_ty = bx.fn_decl_backend_type(fn_abi, llfn);
 
             bx.call(
                 fn_ty,
diff --git a/compiler/rustc_codegen_ssa/src/traits/type_.rs b/compiler/rustc_codegen_ssa/src/traits/type_.rs
index 32c24965e1bf6..3caa959ef3d25 100644
--- a/compiler/rustc_codegen_ssa/src/traits/type_.rs
+++ b/compiler/rustc_codegen_ssa/src/traits/type_.rs
@@ -114,7 +114,11 @@ pub trait LayoutTypeCodegenMethods<'tcx>: BackendTypes {
     /// such as when it's stack-allocated or when it's being loaded or stored.
     fn backend_type(&self, layout: TyAndLayout<'tcx>) -> Self::Type;
     fn cast_backend_type(&self, ty: &CastTarget) -> Self::Type;
-    fn fn_decl_backend_type(&self, fn_abi: &FnAbi<'tcx, Ty<'tcx>>) -> Self::Type;
+    fn fn_decl_backend_type(
+        &self,
+        fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
+        fn_ptr: Self::Value,
+    ) -> Self::Type;
     fn fn_ptr_backend_type(&self, fn_abi: &FnAbi<'tcx, Ty<'tcx>>) -> Self::Type;
     fn reg_backend_type(&self, ty: &Reg) -> Self::Type;
     /// The backend type used for a rust type when it's in an SSA register.

From 4b42195fc3ac51a55b92f559df70b64b066bdc73 Mon Sep 17 00:00:00 2001
From: sayantn <sayantn05@gmail.com>
Date: Fri, 30 May 2025 12:19:41 +0530
Subject: [PATCH 2/7] Check for AutoUpgraded intrinsics, and emit a hard error
 for unknown intrinsics

---
 compiler/rustc_codegen_llvm/src/abi.rs        |  35 ++++-
 compiler/rustc_codegen_llvm/src/builder.rs    | 147 ++++++++++++------
 compiler/rustc_codegen_llvm/src/declare.rs    |  22 ++-
 compiler/rustc_codegen_llvm/src/llvm/ffi.rs   |   8 +
 compiler/rustc_codegen_llvm/src/type_.rs      |  10 ++
 .../rustc_llvm/llvm-wrapper/RustWrapper.cpp   |  12 ++
 6 files changed, 183 insertions(+), 51 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index abfa3315b12fd..2957e4fa97986 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -7,6 +7,7 @@ use rustc_abi::{
     X86Call,
 };
 use rustc_codegen_ssa::MemFlags;
+use rustc_codegen_ssa::common::TypeKind;
 use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
 use rustc_codegen_ssa::mir::place::{PlaceRef, PlaceValue};
 use rustc_codegen_ssa::traits::*;
@@ -22,7 +23,7 @@ use smallvec::SmallVec;
 
 use crate::attributes::{self, llfn_attrs_from_instance};
 use crate::builder::Builder;
-use crate::context::CodegenCx;
+use crate::context::{CodegenCx, GenericCx, SCx};
 use crate::llvm::{self, Attribute, AttributePlace, Type, Value};
 use crate::llvm_util;
 use crate::type_of::LayoutLlvmExt;
@@ -353,6 +354,36 @@ pub(crate) trait FnAbiLlvmExt<'ll, 'tcx> {
     );
 }
 
+impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
+    pub(crate) fn equate_ty(&self, rust_ty: &'ll Type, llvm_ty: &'ll Type) -> bool {
+        if rust_ty == llvm_ty {
+            return true;
+        }
+
+        // Some LLVM intrinsics return **non-packed** structs, but they can't be mimicked from Rust
+        // due to auto field-alignment in non-packed structs (packed structs are represented in LLVM
+        // as, well, packed structs, so they won't match with those either)
+        if self.type_kind(llvm_ty) == TypeKind::Struct
+            && self.type_kind(rust_ty) == TypeKind::Struct
+        {
+            let rust_element_tys = self.struct_element_types(rust_ty);
+            let llvm_element_tys = self.struct_element_types(llvm_ty);
+
+            if rust_element_tys.len() != llvm_element_tys.len() {
+                return false;
+            }
+
+            iter::zip(rust_element_tys, llvm_element_tys).all(
+                |(rust_element_ty, llvm_element_ty)| {
+                    self.equate_ty(rust_element_ty, llvm_element_ty)
+                },
+            )
+        } else {
+            false
+        }
+    }
+}
+
 impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
     fn llvm_return_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type {
         match &self.ret.mode {
@@ -442,7 +473,7 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
 
         iter::once((rust_return_ty, llvm_return_ty))
             .chain(iter::zip(rust_argument_tys, llvm_argument_tys))
-            .all(|(rust_ty, llvm_ty)| rust_ty == llvm_ty)
+            .all(|(rust_ty, llvm_ty)| cx.equate_ty(rust_ty, llvm_ty))
     }
 
     fn llvm_type(
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index c4ad0395f2631..e714f216e4749 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -68,7 +68,6 @@ impl<'a, 'll> SBuilder<'a, 'll> {
     ) -> &'ll Value {
         debug!("call {:?} with args ({:?})", llfn, args);
 
-        let args = self.check_call("call", llty, llfn, args);
         let funclet_bundle = funclet.map(|funclet| funclet.bundle());
         let mut bundles: SmallVec<[_; 2]> = SmallVec::new();
         if let Some(funclet_bundle) = funclet_bundle {
@@ -412,7 +411,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
     ) -> &'ll Value {
         debug!("invoke {:?} with args ({:?})", llfn, args);
 
-        let args = self.check_call("invoke", llty, llfn, args);
+        let args = self.cast_arguments("invoke", llty, llfn, args, fn_abi.is_some());
         let funclet_bundle = funclet.map(|funclet| funclet.bundle());
         let mut bundles: SmallVec<[_; 2]> = SmallVec::new();
         if let Some(funclet_bundle) = funclet_bundle {
@@ -444,8 +443,10 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         };
         if let Some(fn_abi) = fn_abi {
             fn_abi.apply_attrs_callsite(self, invoke, llfn);
+            self.cast_return(fn_abi, llfn, invoke)
+        } else {
+            invoke
         }
-        invoke
     }
 
     fn unreachable(&mut self) {
@@ -1393,7 +1394,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
     ) -> &'ll Value {
         debug!("call {:?} with args ({:?})", llfn, args);
 
-        let args = self.check_call("call", llty, llfn, args);
+        let args = self.cast_arguments("call", llty, llfn, args, fn_abi.is_some());
         let funclet_bundle = funclet.map(|funclet| funclet.bundle());
         let mut bundles: SmallVec<[_; 2]> = SmallVec::new();
         if let Some(funclet_bundle) = funclet_bundle {
@@ -1446,8 +1447,10 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
 
         if let Some(fn_abi) = fn_abi {
             fn_abi.apply_attrs_callsite(self, call, llfn);
+            self.cast_return(fn_abi, llfn, call)
+        } else {
+            call
         }
-        call
     }
 
     fn tail_call(
@@ -1628,47 +1631,6 @@ impl<'a, 'll, CX: Borrow<SCx<'ll>>> GenericBuilder<'a, 'll, CX> {
         ret.expect("LLVM does not have support for catchret")
     }
 
-    fn check_call<'b>(
-        &mut self,
-        typ: &str,
-        fn_ty: &'ll Type,
-        llfn: &'ll Value,
-        args: &'b [&'ll Value],
-    ) -> Cow<'b, [&'ll Value]> {
-        assert!(
-            self.cx.type_kind(fn_ty) == TypeKind::Function,
-            "builder::{typ} not passed a function, but {fn_ty:?}"
-        );
-
-        let param_tys = self.cx.func_params_types(fn_ty);
-
-        let all_args_match = iter::zip(&param_tys, args.iter().map(|&v| self.cx.val_ty(v)))
-            .all(|(expected_ty, actual_ty)| *expected_ty == actual_ty);
-
-        if all_args_match {
-            return Cow::Borrowed(args);
-        }
-
-        let casted_args: Vec<_> = iter::zip(param_tys, args)
-            .enumerate()
-            .map(|(i, (expected_ty, &actual_val))| {
-                let actual_ty = self.cx.val_ty(actual_val);
-                if expected_ty != actual_ty {
-                    debug!(
-                        "type mismatch in function call of {:?}. \
-                            Expected {:?} for param {}, got {:?}; injecting bitcast",
-                        llfn, expected_ty, i, actual_ty
-                    );
-                    self.bitcast(actual_val, expected_ty)
-                } else {
-                    actual_val
-                }
-            })
-            .collect();
-
-        Cow::Owned(casted_args)
-    }
-
     pub(crate) fn va_arg(&mut self, list: &'ll Value, ty: &'ll Type) -> &'ll Value {
         unsafe { llvm::LLVMBuildVAArg(self.llbuilder, list, ty, UNNAMED) }
     }
@@ -1724,6 +1686,93 @@ impl<'a, 'll, CX: Borrow<SCx<'ll>>> GenericBuilder<'a, 'll, CX> {
     }
 }
 impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
+    fn autocast(
+        &mut self,
+        llfn: &'ll Value,
+        val: &'ll Value,
+        src_ty: &'ll Type,
+        dest_ty: &'ll Type,
+        is_argument: bool,
+    ) -> &'ll Value {
+        let (rust_ty, llvm_ty) = if is_argument { (src_ty, dest_ty) } else { (dest_ty, src_ty) };
+
+        if rust_ty == llvm_ty {
+            return val;
+        }
+
+        match self.type_kind(llvm_ty) {
+            TypeKind::Struct => {
+                let mut ret = self.const_poison(dest_ty);
+                for (idx, (src_element_ty, dest_element_ty)) in
+                    iter::zip(self.struct_element_types(src_ty), self.struct_element_types(dest_ty))
+                        .enumerate()
+                {
+                    let elt = self.extract_value(val, idx as u64);
+                    let casted_elt =
+                        self.autocast(llfn, elt, src_element_ty, dest_element_ty, is_argument);
+                    ret = self.insert_value(ret, casted_elt, idx as u64);
+                }
+                ret
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    fn cast_arguments<'b>(
+        &mut self,
+        typ: &str,
+        fn_ty: &'ll Type,
+        llfn: &'ll Value,
+        args: &'b [&'ll Value],
+        has_fnabi: bool,
+    ) -> Cow<'b, [&'ll Value]> {
+        assert_eq!(
+            self.type_kind(fn_ty),
+            TypeKind::Function,
+            "{typ} not passed a function, but {fn_ty:?}"
+        );
+
+        let param_tys = self.func_params_types(fn_ty);
+
+        let mut casted_args = Cow::Borrowed(args);
+
+        for (idx, (dest_ty, &arg)) in iter::zip(param_tys, args).enumerate() {
+            let src_ty = self.val_ty(arg);
+            assert!(
+                self.equate_ty(src_ty, dest_ty),
+                "Cannot match `{dest_ty:?}` (expected) with `{src_ty:?}` (found) in `{llfn:?}`"
+            );
+
+            let casted_arg = self.autocast(llfn, arg, src_ty, dest_ty, true);
+            if arg != casted_arg {
+                assert!(
+                    has_fnabi,
+                    "Should inject autocasts in function call of {llfn:?}, but not able to get Rust signature"
+                );
+
+                casted_args.to_mut()[idx] = casted_arg;
+            }
+        }
+
+        casted_args
+    }
+
+    fn cast_return(
+        &mut self,
+        fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
+        llfn: &'ll Value,
+        ret: &'ll Value,
+    ) -> &'ll Value {
+        let src_ty = self.val_ty(ret);
+        let dest_ty = fn_abi.llvm_return_type(self);
+        assert!(
+            self.equate_ty(dest_ty, src_ty),
+            "Cannot match `{src_ty:?}` (expected) with `{dest_ty:?}` (found) in `{llfn:?}`"
+        );
+
+        self.autocast(llfn, ret, src_ty, dest_ty, false)
+    }
+
     pub(crate) fn landing_pad(
         &mut self,
         ty: &'ll Type,
@@ -1753,7 +1802,7 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
     ) -> &'ll Value {
         debug!("invoke {:?} with args ({:?})", llfn, args);
 
-        let args = self.check_call("callbr", llty, llfn, args);
+        let args = self.cast_arguments("callbr", llty, llfn, args, fn_abi.is_some());
         let funclet_bundle = funclet.map(|funclet| funclet.bundle());
         let mut bundles: SmallVec<[_; 2]> = SmallVec::new();
         if let Some(funclet_bundle) = funclet_bundle {
@@ -1786,8 +1835,10 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
         };
         if let Some(fn_abi) = fn_abi {
             fn_abi.apply_attrs_callsite(self, callbr, llfn);
+            self.cast_return(fn_abi, llfn, callbr)
+        } else {
+            callbr
         }
-        callbr
     }
 
     // Emits CFI pointer type membership tests.
diff --git a/compiler/rustc_codegen_llvm/src/declare.rs b/compiler/rustc_codegen_llvm/src/declare.rs
index 73350e691d1f4..a00e8c62b08f8 100644
--- a/compiler/rustc_codegen_llvm/src/declare.rs
+++ b/compiler/rustc_codegen_llvm/src/declare.rs
@@ -175,7 +175,27 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
             fn_abi.apply_attrs_llfn(self, llfn, instance);
         }
 
-        // todo: check for upgrades, and emit error if not upgradable
+        if let FunctionSignature::MaybeInvalidIntrinsic(..) = signature {
+            let mut new_llfn = None;
+            let can_upgrade =
+                unsafe { llvm::LLVMRustUpgradeIntrinsicFunction(llfn, &mut new_llfn, false) };
+
+            if can_upgrade {
+                // not all intrinsics are upgraded to some other intrinsics, most are upgraded to instruction sequences
+                if let Some(new_llfn) = new_llfn {
+                    self.tcx.dcx().note(format!(
+                        "Using deprecated intrinsic `{name}`, `{}` can be used instead",
+                        str::from_utf8(&llvm::get_value_name(new_llfn)).unwrap()
+                    ));
+                } else {
+                    self.tcx.dcx().note(format!(
+                        "Using deprecated intrinsic `{name}`, consider using other intrinsics/instructions"
+                    ));
+                }
+            } else {
+                self.tcx.dcx().fatal(format!("Invalid LLVM intrinsic: `{name}`"))
+            }
+        }
 
         if self.tcx.sess.is_sanitizer_cfi_enabled() {
             if let Some(instance) = instance {
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 25556b6874ad7..5d3e382fdc8f3 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -1134,6 +1134,11 @@ unsafe extern "C" {
         ParamTypes: *const &'a Type,
         ParamCount: size_t,
     ) -> &'a Value;
+    pub(crate) fn LLVMRustUpgradeIntrinsicFunction<'a>(
+        Fn: &'a Value,
+        NewFn: &mut Option<&'a Value>,
+        CanUpgradeDebugIntrinsicsToRecords: bool,
+    ) -> bool;
 
     // Operations on parameters
     pub(crate) fn LLVMIsAArgument(Val: &Value) -> Option<&Value>;
@@ -1650,6 +1655,9 @@ unsafe extern "C" {
         Packed: Bool,
     );
 
+    pub(crate) fn LLVMCountStructElementTypes(StructTy: &Type) -> c_uint;
+    pub(crate) fn LLVMGetStructElementTypes<'a>(StructTy: &'a Type, Dest: *mut &'a Type);
+
     pub(crate) safe fn LLVMMetadataAsValue<'a>(C: &'a Context, MD: &'a Metadata) -> &'a Value;
 
     pub(crate) safe fn LLVMSetUnnamedAddress(Global: &Value, UnnamedAddr: UnnamedAddr);
diff --git a/compiler/rustc_codegen_llvm/src/type_.rs b/compiler/rustc_codegen_llvm/src/type_.rs
index 44d0268b7a9ef..f2d749f4a5023 100644
--- a/compiler/rustc_codegen_llvm/src/type_.rs
+++ b/compiler/rustc_codegen_llvm/src/type_.rs
@@ -85,6 +85,16 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
     pub(crate) fn func_is_variadic(&self, ty: &'ll Type) -> bool {
         unsafe { llvm::LLVMIsFunctionVarArg(ty).is_true() }
     }
+
+    pub(crate) fn struct_element_types(&self, ty: &'ll Type) -> Vec<&'ll Type> {
+        unsafe {
+            let n_args = llvm::LLVMCountStructElementTypes(ty) as usize;
+            let mut args = Vec::with_capacity(n_args);
+            llvm::LLVMGetStructElementTypes(ty, args.as_mut_ptr());
+            args.set_len(n_args);
+            args
+        }
+    }
 }
 impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
     pub(crate) fn type_bool(&self) -> &'ll Type {
diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index e38474f09ff7a..06dcd5d6c3629 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -9,6 +9,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/BinaryFormat/Magic.h"
 #include "llvm/Bitcode/BitcodeWriter.h"
+#include "llvm/IR/AutoUpgrade.h"
 #include "llvm/IR/DIBuilder.h"
 #include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DiagnosticHandler.h"
@@ -1765,6 +1766,17 @@ extern "C" void LLVMRustGetMangledName(LLVMValueRef V, RustStringRef Str) {
   Mangler().getNameWithPrefix(OS, GV, true);
 }
 
+extern "C" bool
+LLVMRustUpgradeIntrinsicFunction(LLVMValueRef Fn, LLVMValueRef *NewFn,
+                                 bool canUpgradeDebugIntrinsicsToRecords) {
+  Function *F = unwrap<Function>(Fn);
+  Function *NewF = nullptr;
+  bool CanUpgrade =
+      UpgradeIntrinsicFunction(F, NewF, canUpgradeDebugIntrinsicsToRecords);
+  *NewFn = wrap(NewF);
+  return CanUpgrade;
+}
+
 extern "C" int32_t LLVMRustGetElementTypeArgIndex(LLVMValueRef CallSite) {
   auto *CB = unwrap<CallBase>(CallSite);
   switch (CB->getIntrinsicID()) {

From bba9fce08b4adb1d2aebe28830006878f0135f2e Mon Sep 17 00:00:00 2001
From: sayantn <sayantn05@gmail.com>
Date: Fri, 30 May 2025 23:22:11 +0530
Subject: [PATCH 3/7] Add autocast tests  - Correct usage of invalid intrinsics
 in tests

---
 tests/run-make/simd-ffi/simd.rs               |  2 +-
 tests/ui/codegen/deprecated-llvm-intrinsic.rs | 28 +++++++++++++++++++
 .../codegen/deprecated-llvm-intrinsic.stderr  |  2 ++
 .../incorrect-llvm-intrinsic-signature.rs     | 15 ++++++++++
 .../incorrect-llvm-intrinsic-signature.stderr |  4 +++
 tests/ui/codegen/invalid-llvm-intrinsic.rs    | 15 ++++++++++
 .../ui/codegen/invalid-llvm-intrinsic.stderr  |  4 +++
 7 files changed, 69 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/codegen/deprecated-llvm-intrinsic.rs
 create mode 100644 tests/ui/codegen/deprecated-llvm-intrinsic.stderr
 create mode 100644 tests/ui/codegen/incorrect-llvm-intrinsic-signature.rs
 create mode 100644 tests/ui/codegen/incorrect-llvm-intrinsic-signature.stderr
 create mode 100644 tests/ui/codegen/invalid-llvm-intrinsic.rs
 create mode 100644 tests/ui/codegen/invalid-llvm-intrinsic.stderr

diff --git a/tests/run-make/simd-ffi/simd.rs b/tests/run-make/simd-ffi/simd.rs
index 1cd961ff87e7b..3f12dabdb65ea 100644
--- a/tests/run-make/simd-ffi/simd.rs
+++ b/tests/run-make/simd-ffi/simd.rs
@@ -35,7 +35,7 @@ extern "C" {
     fn integer(a: i32x4, b: i32x4) -> i32x4;
     // vmaxq_s32
     #[cfg(target_arch = "aarch64")]
-    #[link_name = "llvm.aarch64.neon.maxs.v4i32"]
+    #[link_name = "llvm.aarch64.neon.smax.v4i32"]
     fn integer(a: i32x4, b: i32x4) -> i32x4;
 
     // Use a generic LLVM intrinsic to do type checking on other platforms
diff --git a/tests/ui/codegen/deprecated-llvm-intrinsic.rs b/tests/ui/codegen/deprecated-llvm-intrinsic.rs
new file mode 100644
index 0000000000000..8ae363054cc74
--- /dev/null
+++ b/tests/ui/codegen/deprecated-llvm-intrinsic.rs
@@ -0,0 +1,28 @@
+//@ add-core-stubs
+//@ build-pass
+//@ ignore-pass
+//@ compile-flags: --target aarch64-unknown-linux-gnu
+//@ needs-llvm-components: aarch64
+#![feature(no_core, lang_items, link_llvm_intrinsics, abi_unadjusted, repr_simd, simd_ffi)]
+#![no_std]
+#![no_core]
+#![allow(internal_features, non_camel_case_types, improper_ctypes)]
+#![crate_type = "lib"]
+
+extern crate minicore;
+use minicore::*;
+
+#[repr(simd)]
+pub struct i8x8([i8; 8]);
+
+extern "unadjusted" {
+    #[link_name = "llvm.aarch64.neon.rbit.v8i8"]
+    fn foo(a: i8x8) -> i8x8;
+}
+
+#[target_feature(enable = "neon")]
+pub unsafe fn bar(a: i8x8) -> i8x8 {
+    foo(a)
+}
+
+//~? NOTE: Using deprecated intrinsic `llvm.aarch64.neon.rbit.v8i8`, `llvm.bitreverse.v8i8` can be used instead
diff --git a/tests/ui/codegen/deprecated-llvm-intrinsic.stderr b/tests/ui/codegen/deprecated-llvm-intrinsic.stderr
new file mode 100644
index 0000000000000..214ac269e7d0e
--- /dev/null
+++ b/tests/ui/codegen/deprecated-llvm-intrinsic.stderr
@@ -0,0 +1,2 @@
+note: Using deprecated intrinsic `llvm.aarch64.neon.rbit.v8i8`, `llvm.bitreverse.v8i8` can be used instead
+
diff --git a/tests/ui/codegen/incorrect-llvm-intrinsic-signature.rs b/tests/ui/codegen/incorrect-llvm-intrinsic-signature.rs
new file mode 100644
index 0000000000000..84c4c0d747247
--- /dev/null
+++ b/tests/ui/codegen/incorrect-llvm-intrinsic-signature.rs
@@ -0,0 +1,15 @@
+//@ build-fail
+
+#![feature(link_llvm_intrinsics, abi_unadjusted)]
+#![allow(internal_features, non_camel_case_types, improper_ctypes)]
+
+extern "unadjusted" {
+    #[link_name = "llvm.assume"]
+    fn foo();
+}
+
+pub fn main() {
+    unsafe { foo() }
+}
+
+//~? ERROR: Intrinsic signature mismatch for `llvm.assume`: expected signature `void (i1)`
diff --git a/tests/ui/codegen/incorrect-llvm-intrinsic-signature.stderr b/tests/ui/codegen/incorrect-llvm-intrinsic-signature.stderr
new file mode 100644
index 0000000000000..f67ba8a65a40c
--- /dev/null
+++ b/tests/ui/codegen/incorrect-llvm-intrinsic-signature.stderr
@@ -0,0 +1,4 @@
+error: Intrinsic signature mismatch for `llvm.assume`: expected signature `void (i1)`
+
+error: aborting due to 1 previous error
+
diff --git a/tests/ui/codegen/invalid-llvm-intrinsic.rs b/tests/ui/codegen/invalid-llvm-intrinsic.rs
new file mode 100644
index 0000000000000..2f1ff826ed39b
--- /dev/null
+++ b/tests/ui/codegen/invalid-llvm-intrinsic.rs
@@ -0,0 +1,15 @@
+//@ build-fail
+
+#![feature(link_llvm_intrinsics, abi_unadjusted)]
+#![allow(internal_features, non_camel_case_types, improper_ctypes)]
+
+extern "unadjusted" {
+    #[link_name = "llvm.abcde"]
+    fn foo();
+}
+
+pub fn main() {
+    unsafe { foo() }
+}
+
+//~? ERROR: Invalid LLVM intrinsic: `llvm.abcde`
diff --git a/tests/ui/codegen/invalid-llvm-intrinsic.stderr b/tests/ui/codegen/invalid-llvm-intrinsic.stderr
new file mode 100644
index 0000000000000..467d6a62553cc
--- /dev/null
+++ b/tests/ui/codegen/invalid-llvm-intrinsic.stderr
@@ -0,0 +1,4 @@
+error: Invalid LLVM intrinsic: `llvm.abcde`
+
+error: aborting due to 1 previous error
+

From c5d2aecf8df8e86f131bf04dae85ef05a10019bf Mon Sep 17 00:00:00 2001
From: sayantn <sayantn05@gmail.com>
Date: Tue, 10 Jun 2025 11:40:10 +0530
Subject: [PATCH 4/7] Refactor emitting errors to `declare.rs`, and use
 fluently-generated error messages

Create lints for deprecated and invalid intrinsics
---
 compiler/rustc_codegen_llvm/messages.ftl      |  4 +
 compiler/rustc_codegen_llvm/src/abi.rs        | 95 ++++++++-----------
 compiler/rustc_codegen_llvm/src/declare.rs    | 94 ++++++++++--------
 compiler/rustc_codegen_llvm/src/errors.rs     | 10 ++
 compiler/rustc_codegen_llvm/src/intrinsic.rs  |  2 +-
 compiler/rustc_codegen_llvm/src/type_.rs      |  2 +-
 compiler/rustc_lint_defs/src/builtin.rs       | 78 +++++++++++++++
 tests/ui/codegen/deprecated-llvm-intrinsic.rs |  4 +-
 .../codegen/deprecated-llvm-intrinsic.stderr  | 14 ++-
 .../incorrect-llvm-intrinsic-signature.rs     |  4 +-
 .../incorrect-llvm-intrinsic-signature.stderr |  6 +-
 tests/ui/codegen/invalid-llvm-intrinsic.rs    |  4 +-
 .../ui/codegen/invalid-llvm-intrinsic.stderr  |  8 +-
 13 files changed, 220 insertions(+), 105 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/messages.ftl b/compiler/rustc_codegen_llvm/messages.ftl
index ce9a51b539d83..08e8de44a10b5 100644
--- a/compiler/rustc_codegen_llvm/messages.ftl
+++ b/compiler/rustc_codegen_llvm/messages.ftl
@@ -9,6 +9,10 @@ codegen_llvm_from_llvm_diag = {$message}
 
 codegen_llvm_from_llvm_optimization_diag = {$filename}:{$line}:{$column} {$pass_name} ({$kind}): {$message}
 
+codegen_llvm_intrinsic_signature_mismatch =
+    intrinsic signature mismatch for `{$name}`: expected signature `{$llvm_fn_ty}`, found `{$rust_fn_ty}`
+
+
 codegen_llvm_load_bitcode = failed to load bitcode of module "{$name}"
 codegen_llvm_load_bitcode_with_llvm_err = failed to load bitcode of module "{$name}": {$llvm_err}
 
diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index 2957e4fa97986..f552eca5e21e3 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -304,20 +304,32 @@ impl<'ll, 'tcx> ArgAbiBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
 }
 
 pub(crate) enum FunctionSignature<'ll> {
-    /// The signature is obtained directly from LLVM, and **may not match the Rust signature**
-    Intrinsic(&'ll Type),
+    /// This is an LLVM intrinsic, the signature is obtained directly from LLVM, and **may not match the Rust signature**
+    LLVMSignature(llvm::Intrinsic, &'ll Type),
+    /// This is an LLVM intrinsic, but the signature is just the Rust signature.
+    /// FIXME: this should ideally not exist, we should be using the LLVM signature for all LLVM intrinsics
+    RustSignature(llvm::Intrinsic, &'ll Type),
     /// The name starts with `llvm.`, but can't obtain the intrinsic ID. May be invalid or upgradable
-    MaybeInvalidIntrinsic(&'ll Type),
+    MaybeInvalid(&'ll Type),
     /// Just the Rust signature
-    Rust(&'ll Type),
+    NotIntrinsic(&'ll Type),
 }
 
 impl<'ll> FunctionSignature<'ll> {
     pub(crate) fn fn_ty(&self) -> &'ll Type {
         match self {
-            FunctionSignature::Intrinsic(fn_ty)
-            | FunctionSignature::MaybeInvalidIntrinsic(fn_ty)
-            | FunctionSignature::Rust(fn_ty) => fn_ty,
+            FunctionSignature::LLVMSignature(_, fn_ty)
+            | FunctionSignature::RustSignature(_, fn_ty)
+            | FunctionSignature::MaybeInvalid(fn_ty)
+            | FunctionSignature::NotIntrinsic(fn_ty) => fn_ty,
+        }
+    }
+
+    pub(crate) fn intrinsic(&self) -> Option<llvm::Intrinsic> {
+        match self {
+            FunctionSignature::RustSignature(intrinsic, _)
+            | FunctionSignature::LLVMSignature(intrinsic, _) => Some(*intrinsic),
+            _ => None,
         }
     }
 }
@@ -325,12 +337,9 @@ impl<'ll> FunctionSignature<'ll> {
 pub(crate) trait FnAbiLlvmExt<'ll, 'tcx> {
     fn llvm_return_type(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type;
     fn llvm_argument_types(&self, cx: &CodegenCx<'ll, 'tcx>) -> Vec<&'ll Type>;
-    fn llvm_type(
-        &self,
-        cx: &CodegenCx<'ll, 'tcx>,
-        name: &[u8],
-        do_verify: bool,
-    ) -> FunctionSignature<'ll>;
+    fn llvm_type(&self, cx: &CodegenCx<'ll, 'tcx>, name: &[u8]) -> FunctionSignature<'ll>;
+    /// The normal Rust signature for this
+    fn rust_signature(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type;
     /// **If this function is an LLVM intrinsic** checks if the LLVM signature provided matches with this
     fn verify_intrinsic_signature(&self, cx: &CodegenCx<'ll, 'tcx>, llvm_ty: &'ll Type) -> bool;
 
@@ -476,51 +485,35 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
             .all(|(rust_ty, llvm_ty)| cx.equate_ty(rust_ty, llvm_ty))
     }
 
-    fn llvm_type(
-        &self,
-        cx: &CodegenCx<'ll, 'tcx>,
-        name: &[u8],
-        do_verify: bool,
-    ) -> FunctionSignature<'ll> {
-        let mut maybe_invalid = false;
+    fn rust_signature(&self, cx: &CodegenCx<'ll, 'tcx>) -> &'ll Type {
+        let return_ty = self.llvm_return_type(cx);
+        let argument_tys = self.llvm_argument_types(cx);
 
+        if self.c_variadic {
+            cx.type_variadic_func(&argument_tys, return_ty)
+        } else {
+            cx.type_func(&argument_tys, return_ty)
+        }
+    }
+
+    fn llvm_type(&self, cx: &CodegenCx<'ll, 'tcx>, name: &[u8]) -> FunctionSignature<'ll> {
         if name.starts_with(b"llvm.") {
             if let Some(intrinsic) = llvm::Intrinsic::lookup(name) {
                 if !intrinsic.is_overloaded() {
                     // FIXME: also do this for overloaded intrinsics
-                    let llvm_fn_ty = intrinsic.get_type(cx.llcx, &[]);
-                    if do_verify {
-                        if !self.verify_intrinsic_signature(cx, llvm_fn_ty) {
-                            cx.tcx.dcx().fatal(format!(
-                                "Intrinsic signature mismatch for `{}`: expected signature `{llvm_fn_ty:?}`",
-                                str::from_utf8(name).unwrap()
-                            ));
-                        }
-                    }
-                    return FunctionSignature::Intrinsic(llvm_fn_ty);
+                    FunctionSignature::LLVMSignature(intrinsic, intrinsic.get_type(cx.llcx, &[]))
+                } else {
+                    FunctionSignature::RustSignature(intrinsic, self.rust_signature(cx))
                 }
             } else {
                 // it's one of 2 cases,
                 // - either the base name is invalid
                 // - it has been superseded by something else, so the intrinsic was removed entirely
                 // to check for upgrades, we need the `llfn`, so we defer it for now
-                maybe_invalid = true;
+                FunctionSignature::MaybeInvalid(self.rust_signature(cx))
             }
-        }
-
-        let return_ty = self.llvm_return_type(cx);
-        let argument_tys = self.llvm_argument_types(cx);
-
-        let fn_ty = if self.c_variadic {
-            cx.type_variadic_func(&argument_tys, return_ty)
         } else {
-            cx.type_func(&argument_tys, return_ty)
-        };
-
-        if maybe_invalid {
-            FunctionSignature::MaybeInvalidIntrinsic(fn_ty)
-        } else {
-            FunctionSignature::Rust(fn_ty)
+            FunctionSignature::NotIntrinsic(self.rust_signature(cx))
         }
     }
 
@@ -684,15 +677,9 @@ impl<'ll, 'tcx> FnAbiLlvmExt<'ll, 'tcx> for FnAbi<'tcx, Ty<'tcx>> {
         callsite: &'ll Value,
         llfn: &'ll Value,
     ) {
-        // if we are using the LLVM signature, use the LLVM attributes otherwise it might be problematic
-        let name = llvm::get_value_name(llfn);
-        if name.starts_with(b"llvm.")
-            && let Some(intrinsic) = llvm::Intrinsic::lookup(&name)
-        {
-            // FIXME: also do this for overloaded intrinsics
-            if !intrinsic.is_overloaded() {
-                return;
-            }
+        // Don't apply any attributes to LLVM intrinsics, they will be applied by AutoUpgrade
+        if llvm::get_value_name(llfn).starts_with(b"llvm.") {
+            return;
         }
 
         let mut func_attrs = SmallVec::<[_; 2]>::new();
diff --git a/compiler/rustc_codegen_llvm/src/declare.rs b/compiler/rustc_codegen_llvm/src/declare.rs
index a00e8c62b08f8..981155c35edae 100644
--- a/compiler/rustc_codegen_llvm/src/declare.rs
+++ b/compiler/rustc_codegen_llvm/src/declare.rs
@@ -18,16 +18,17 @@ use rustc_codegen_ssa::traits::TypeMembershipCodegenMethods;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_middle::ty::{Instance, Ty};
 use rustc_sanitizers::{cfi, kcfi};
+use rustc_session::lint::builtin::{DEPRECATED_LLVM_INTRINSIC, UNKNOWN_LLVM_INTRINSIC};
 use rustc_target::callconv::FnAbi;
 use smallvec::SmallVec;
 use tracing::debug;
 
 use crate::abi::{FnAbiLlvmExt, FunctionSignature};
-use crate::attributes;
 use crate::common::AsCCharPtr;
 use crate::context::{CodegenCx, GenericCx, SCx, SimpleCx};
 use crate::llvm::AttributePlace::Function;
 use crate::llvm::{self, FromGeneric, Type, Value, Visibility};
+use crate::{attributes, errors};
 
 /// Declare a function with a SimpleCx.
 ///
@@ -148,52 +149,69 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
     ) -> &'ll Value {
         debug!("declare_rust_fn(name={:?}, fn_abi={:?})", name, fn_abi);
 
-        let signature = fn_abi.llvm_type(self, name.as_bytes(), true);
-        let llfn;
-
-        if let FunctionSignature::Intrinsic(fn_ty) = signature {
-            // intrinsics have a specified set of attributes, so we don't use the `FnAbi` set for them
-            llfn = declare_simple_fn(
-                self,
-                name,
-                fn_abi.llvm_cconv(self),
-                llvm::UnnamedAddr::Global,
-                llvm::Visibility::Default,
-                fn_ty,
-            );
-        } else {
-            // Function addresses in Rust are never significant, allowing functions to
-            // be merged.
-            llfn = declare_raw_fn(
-                self,
-                name,
-                fn_abi.llvm_cconv(self),
-                llvm::UnnamedAddr::Global,
-                llvm::Visibility::Default,
-                signature.fn_ty(),
-            );
+        let signature = fn_abi.llvm_type(self, name.as_bytes());
+
+        let span = || instance.map(|instance| self.tcx.def_span(instance.def_id()));
+
+        if let FunctionSignature::LLVMSignature(_, llvm_fn_ty) = signature {
+            // check if the intrinsic signatures match
+            if !fn_abi.verify_intrinsic_signature(self, llvm_fn_ty) {
+                self.tcx.dcx().emit_fatal(errors::IntrinsicSignatureMismatch {
+                    name,
+                    llvm_fn_ty: &format!("{llvm_fn_ty:?}"),
+                    rust_fn_ty: &format!("{:?}", fn_abi.rust_signature(self)),
+                    span: span(),
+                });
+            }
+        }
+
+        // Function addresses in Rust are never significant, allowing functions to
+        // be merged.
+        let llfn = declare_raw_fn(
+            self,
+            name,
+            fn_abi.llvm_cconv(self),
+            llvm::UnnamedAddr::Global,
+            llvm::Visibility::Default,
+            signature.fn_ty(),
+        );
+
+        if signature.intrinsic().is_none() {
+            // Don't apply any attributes to intrinsics, they will be applied by AutoUpgrade
             fn_abi.apply_attrs_llfn(self, llfn, instance);
         }
 
-        if let FunctionSignature::MaybeInvalidIntrinsic(..) = signature {
+        if let FunctionSignature::MaybeInvalid(..) = signature {
             let mut new_llfn = None;
             let can_upgrade =
                 unsafe { llvm::LLVMRustUpgradeIntrinsicFunction(llfn, &mut new_llfn, false) };
 
-            if can_upgrade {
-                // not all intrinsics are upgraded to some other intrinsics, most are upgraded to instruction sequences
-                if let Some(new_llfn) = new_llfn {
-                    self.tcx.dcx().note(format!(
-                        "Using deprecated intrinsic `{name}`, `{}` can be used instead",
-                        str::from_utf8(&llvm::get_value_name(new_llfn)).unwrap()
-                    ));
+            // we can emit diagnostics for local crates only
+            if let Some(instance) = instance
+                && let Some(local_def_id) = instance.def_id().as_local()
+            {
+                let hir_id = self.tcx.local_def_id_to_hir_id(local_def_id);
+                let span = self.tcx.def_span(local_def_id);
+
+                if can_upgrade {
+                    // not all intrinsics are upgraded to some other intrinsics, most are upgraded to instruction sequences
+                    let msg = if let Some(new_llfn) = new_llfn {
+                        format!(
+                            "using deprecated intrinsic `{name}`, `{}` can be used instead",
+                            str::from_utf8(&llvm::get_value_name(new_llfn)).unwrap()
+                        )
+                    } else {
+                        format!("using deprecated intrinsic `{name}`")
+                    };
+                    self.tcx.node_lint(DEPRECATED_LLVM_INTRINSIC, hir_id, |d| {
+                        d.primary_message(msg).span(span);
+                    });
                 } else {
-                    self.tcx.dcx().note(format!(
-                        "Using deprecated intrinsic `{name}`, consider using other intrinsics/instructions"
-                    ));
+                    // This is either plain wrong, or this can be caused by incompatible LLVM versions, we let the user decide
+                    self.tcx.node_lint(UNKNOWN_LLVM_INTRINSIC, hir_id, |d| {
+                        d.primary_message(format!("invalid LLVM Intrinsic `{name}`")).span(span);
+                    });
                 }
-            } else {
-                self.tcx.dcx().fatal(format!("Invalid LLVM intrinsic: `{name}`"))
             }
         }
 
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 627b0c9ff3b33..8db8f3160c11b 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -147,3 +147,13 @@ pub(crate) struct FixedX18InvalidArch<'a> {
 #[derive(Diagnostic)]
 #[diag(codegen_llvm_sanitizer_kcfi_arity_requires_llvm_21_0_0)]
 pub(crate) struct SanitizerKcfiArityRequiresLLVM2100;
+
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_intrinsic_signature_mismatch)]
+pub(crate) struct IntrinsicSignatureMismatch<'a> {
+    pub name: &'a str,
+    pub llvm_fn_ty: &'a str,
+    pub rust_fn_ty: &'a str,
+    #[primary_span]
+    pub span: Option<Span>,
+}
diff --git a/compiler/rustc_codegen_llvm/src/intrinsic.rs b/compiler/rustc_codegen_llvm/src/intrinsic.rs
index da5f5a9afb909..b25c6cc4be0ee 100644
--- a/compiler/rustc_codegen_llvm/src/intrinsic.rs
+++ b/compiler/rustc_codegen_llvm/src/intrinsic.rs
@@ -1073,7 +1073,7 @@ fn gen_fn<'a, 'll, 'tcx>(
     codegen: &mut dyn FnMut(Builder<'a, 'll, 'tcx>),
 ) -> (&'ll Type, &'ll Value) {
     let fn_abi = cx.fn_abi_of_fn_ptr(rust_fn_sig, ty::List::empty());
-    let llty = fn_abi.llvm_type(cx, name.as_bytes(), true).fn_ty();
+    let llty = fn_abi.llvm_type(cx, name.as_bytes()).fn_ty();
     let llfn = cx.declare_fn(name, fn_abi, None);
     cx.set_frame_pointer_type(llfn);
     cx.apply_target_cpu_attr(llfn);
diff --git a/compiler/rustc_codegen_llvm/src/type_.rs b/compiler/rustc_codegen_llvm/src/type_.rs
index f2d749f4a5023..371162583a892 100644
--- a/compiler/rustc_codegen_llvm/src/type_.rs
+++ b/compiler/rustc_codegen_llvm/src/type_.rs
@@ -309,7 +309,7 @@ impl<'ll, 'tcx> LayoutTypeCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
         fn_abi: &FnAbi<'tcx, Ty<'tcx>>,
         fn_ptr: &'ll Value,
     ) -> &'ll Type {
-        fn_abi.llvm_type(self, &llvm::get_value_name(fn_ptr), false).fn_ty()
+        fn_abi.llvm_type(self, &llvm::get_value_name(fn_ptr)).fn_ty()
     }
     fn fn_ptr_backend_type(&self, fn_abi: &FnAbi<'tcx, Ty<'tcx>>) -> &'ll Type {
         fn_abi.ptr_to_llvm_type(self)
diff --git a/compiler/rustc_lint_defs/src/builtin.rs b/compiler/rustc_lint_defs/src/builtin.rs
index 939f3d088b12f..5f56af5c9abf6 100644
--- a/compiler/rustc_lint_defs/src/builtin.rs
+++ b/compiler/rustc_lint_defs/src/builtin.rs
@@ -35,6 +35,7 @@ declare_lint_pass! {
         DEPENDENCY_ON_UNIT_NEVER_TYPE_FALLBACK,
         DEPRECATED,
         DEPRECATED_IN_FUTURE,
+        DEPRECATED_LLVM_INTRINSIC,
         DEPRECATED_SAFE_2024,
         DEPRECATED_WHERE_CLAUSE_LOCATION,
         DUPLICATE_MACRO_ATTRIBUTES,
@@ -117,6 +118,7 @@ declare_lint_pass! {
         UNKNOWN_CRATE_TYPES,
         UNKNOWN_DIAGNOSTIC_ATTRIBUTES,
         UNKNOWN_LINTS,
+        UNKNOWN_LLVM_INTRINSIC,
         UNNAMEABLE_TEST_ITEMS,
         UNNAMEABLE_TYPES,
         UNREACHABLE_CODE,
@@ -5197,3 +5199,79 @@ declare_lint! {
     Warn,
     r#"detects when a function annotated with `#[inline(always)]` and `#[target_feature(enable = "..")]` is inlined into a caller without the required target feature"#,
 }
+
+declare_lint! {
+    /// The `unknown_llvm_intrinsic` lint detects usage of unknown LLVM intrinsics.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,compile_fail
+    /// #![feature(link_llvm_intrinsics, abi_unadjusted)]
+    ///
+    /// unsafe extern "unadjusted" {
+    ///     #[link_name = "llvm.abcde"]
+    ///     fn foo();
+    /// }
+    ///
+    /// #[inline(never)]
+    /// pub fn main() {
+    ///     unsafe { foo() }
+    /// }
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// Linking to an unknown LLVM intrinsic may cause linker errors (in general it's UB),
+    /// so this lint captures those undesirable scenarios.
+    pub UNKNOWN_LLVM_INTRINSIC,
+    Deny,
+    "detects uses of unknown LLVM intrinsics",
+    @feature_gate = link_llvm_intrinsics;
+}
+
+declare_lint! {
+    /// The `deprecated_llvm_intrinsic` lint detects usage of deprecated LLVM intrinsics.
+    ///
+    /// ### Example
+    ///
+    /// ```rust,ignore (requires x86)
+    /// #![cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+    /// #![feature(link_llvm_intrinsics, abi_unadjusted)]
+    /// #![deny(deprecated_llvm_intrinsic)]
+    ///
+    /// unsafe extern "unadjusted" {
+    ///     #[link_name = "llvm.x86.addcarryx.u32"]
+    ///     fn foo(a: u8, b: u32, c: u32, d: &mut u32) -> u8;
+    /// }
+    ///
+    /// #[inline(never)]
+    /// #[target_feature(enable = "adx")]
+    /// pub fn bar(a: u8, b: u32, c: u32, d: &mut u32) -> u8 {
+    ///     unsafe { foo(a, b, c, d) }
+    /// }
+    /// ```
+    ///
+    /// This will produce:
+    ///
+    /// ```text
+    /// error: Using deprecated intrinsic `llvm.x86.addcarryx.u32`
+    ///  --> example.rs:7:5
+    ///   |
+    /// 7 |     fn foo(a: u8, b: u32, c: u32, d: &mut u32) -> u8;
+    ///   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+    ///   |
+    /// ```
+    ///
+    /// ### Explanation
+    ///
+    /// LLVM periodically updates its list of intrinsics. Removed intrinsics are unlikely
+    /// to be removed, but they may optimize less well than their new versions, so it's
+    /// best to use the new version. Also, some deprecated intrinsics might have buggy
+    /// behavior
+    pub DEPRECATED_LLVM_INTRINSIC,
+    Allow,
+    "detects uses of deprecated LLVM intrinsics",
+    @feature_gate = link_llvm_intrinsics;
+}
diff --git a/tests/ui/codegen/deprecated-llvm-intrinsic.rs b/tests/ui/codegen/deprecated-llvm-intrinsic.rs
index 8ae363054cc74..9affa7ebd275c 100644
--- a/tests/ui/codegen/deprecated-llvm-intrinsic.rs
+++ b/tests/ui/codegen/deprecated-llvm-intrinsic.rs
@@ -16,13 +16,13 @@ use minicore::*;
 pub struct i8x8([i8; 8]);
 
 extern "unadjusted" {
+    #![warn(deprecated_llvm_intrinsic)]
     #[link_name = "llvm.aarch64.neon.rbit.v8i8"]
     fn foo(a: i8x8) -> i8x8;
+    //~^ WARN: using deprecated intrinsic `llvm.aarch64.neon.rbit.v8i8`, `llvm.bitreverse.v8i8` can be used instead
 }
 
 #[target_feature(enable = "neon")]
 pub unsafe fn bar(a: i8x8) -> i8x8 {
     foo(a)
 }
-
-//~? NOTE: Using deprecated intrinsic `llvm.aarch64.neon.rbit.v8i8`, `llvm.bitreverse.v8i8` can be used instead
diff --git a/tests/ui/codegen/deprecated-llvm-intrinsic.stderr b/tests/ui/codegen/deprecated-llvm-intrinsic.stderr
index 214ac269e7d0e..8348056387eca 100644
--- a/tests/ui/codegen/deprecated-llvm-intrinsic.stderr
+++ b/tests/ui/codegen/deprecated-llvm-intrinsic.stderr
@@ -1,2 +1,14 @@
-note: Using deprecated intrinsic `llvm.aarch64.neon.rbit.v8i8`, `llvm.bitreverse.v8i8` can be used instead
+warning: using deprecated intrinsic `llvm.aarch64.neon.rbit.v8i8`, `llvm.bitreverse.v8i8` can be used instead
+  --> $DIR/deprecated-llvm-intrinsic.rs:21:5
+   |
+LL |     fn foo(a: i8x8) -> i8x8;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/deprecated-llvm-intrinsic.rs:19:13
+   |
+LL |     #![warn(deprecated_llvm_intrinsic)]
+   |             ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+warning: 1 warning emitted
 
diff --git a/tests/ui/codegen/incorrect-llvm-intrinsic-signature.rs b/tests/ui/codegen/incorrect-llvm-intrinsic-signature.rs
index 84c4c0d747247..57d57136fdf23 100644
--- a/tests/ui/codegen/incorrect-llvm-intrinsic-signature.rs
+++ b/tests/ui/codegen/incorrect-llvm-intrinsic-signature.rs
@@ -1,15 +1,13 @@
 //@ build-fail
 
 #![feature(link_llvm_intrinsics, abi_unadjusted)]
-#![allow(internal_features, non_camel_case_types, improper_ctypes)]
 
 extern "unadjusted" {
     #[link_name = "llvm.assume"]
     fn foo();
+    //~^ ERROR: intrinsic signature mismatch for `llvm.assume`: expected signature `void (i1)`, found `void ()`
 }
 
 pub fn main() {
     unsafe { foo() }
 }
-
-//~? ERROR: Intrinsic signature mismatch for `llvm.assume`: expected signature `void (i1)`
diff --git a/tests/ui/codegen/incorrect-llvm-intrinsic-signature.stderr b/tests/ui/codegen/incorrect-llvm-intrinsic-signature.stderr
index f67ba8a65a40c..7499bf00e7593 100644
--- a/tests/ui/codegen/incorrect-llvm-intrinsic-signature.stderr
+++ b/tests/ui/codegen/incorrect-llvm-intrinsic-signature.stderr
@@ -1,4 +1,8 @@
-error: Intrinsic signature mismatch for `llvm.assume`: expected signature `void (i1)`
+error: intrinsic signature mismatch for `llvm.assume`: expected signature `void (i1)`, found `void ()`
+  --> $DIR/incorrect-llvm-intrinsic-signature.rs:7:5
+   |
+LL |     fn foo();
+   |     ^^^^^^^^^
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/codegen/invalid-llvm-intrinsic.rs b/tests/ui/codegen/invalid-llvm-intrinsic.rs
index 2f1ff826ed39b..b9e2d579b908c 100644
--- a/tests/ui/codegen/invalid-llvm-intrinsic.rs
+++ b/tests/ui/codegen/invalid-llvm-intrinsic.rs
@@ -1,15 +1,13 @@
 //@ build-fail
 
 #![feature(link_llvm_intrinsics, abi_unadjusted)]
-#![allow(internal_features, non_camel_case_types, improper_ctypes)]
 
 extern "unadjusted" {
     #[link_name = "llvm.abcde"]
     fn foo();
+    //~^ ERROR: invalid LLVM Intrinsic `llvm.abcde`
 }
 
 pub fn main() {
     unsafe { foo() }
 }
-
-//~? ERROR: Invalid LLVM intrinsic: `llvm.abcde`
diff --git a/tests/ui/codegen/invalid-llvm-intrinsic.stderr b/tests/ui/codegen/invalid-llvm-intrinsic.stderr
index 467d6a62553cc..820a7a2e2ea9f 100644
--- a/tests/ui/codegen/invalid-llvm-intrinsic.stderr
+++ b/tests/ui/codegen/invalid-llvm-intrinsic.stderr
@@ -1,4 +1,10 @@
-error: Invalid LLVM intrinsic: `llvm.abcde`
+error: invalid LLVM Intrinsic `llvm.abcde`
+  --> $DIR/invalid-llvm-intrinsic.rs:7:5
+   |
+LL |     fn foo();
+   |     ^^^^^^^^^
+   |
+   = note: `#[deny(unknown_llvm_intrinsic)]` on by default
 
 error: aborting due to 1 previous error
 

From fd8264e2c6de300298d8fb13b7a2eb7ba02aee6b Mon Sep 17 00:00:00 2001
From: sayantn <sayantn05@gmail.com>
Date: Tue, 10 Jun 2025 13:16:24 +0530
Subject: [PATCH 5/7] Add target arch verification for LLVM intrinsics

---
 compiler/rustc_codegen_llvm/messages.ftl      |  3 ++
 compiler/rustc_codegen_llvm/src/declare.rs    | 31 ++++++++++++++++++-
 compiler/rustc_codegen_llvm/src/errors.rs     |  9 ++++++
 compiler/rustc_codegen_llvm/src/llvm/ffi.rs   |  1 +
 compiler/rustc_codegen_llvm/src/llvm/mod.rs   |  4 +++
 .../rustc_llvm/llvm-wrapper/RustWrapper.cpp   |  8 +++++
 tests/ui/codegen/incorrect-arch-intrinsic.rs  | 17 ++++++++++
 .../codegen/incorrect-arch-intrinsic.stderr   |  8 +++++
 8 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/codegen/incorrect-arch-intrinsic.rs
 create mode 100644 tests/ui/codegen/incorrect-arch-intrinsic.stderr

diff --git a/compiler/rustc_codegen_llvm/messages.ftl b/compiler/rustc_codegen_llvm/messages.ftl
index 08e8de44a10b5..fe996c219fb0e 100644
--- a/compiler/rustc_codegen_llvm/messages.ftl
+++ b/compiler/rustc_codegen_llvm/messages.ftl
@@ -12,6 +12,9 @@ codegen_llvm_from_llvm_optimization_diag = {$filename}:{$line}:{$column} {$pass_
 codegen_llvm_intrinsic_signature_mismatch =
     intrinsic signature mismatch for `{$name}`: expected signature `{$llvm_fn_ty}`, found `{$rust_fn_ty}`
 
+codegen_llvm_intrinsic_wrong_arch =
+    intrinsic `{$name}` cannot be used with target arch `{$target_arch}`
+
 
 codegen_llvm_load_bitcode = failed to load bitcode of module "{$name}"
 codegen_llvm_load_bitcode_with_llvm_err = failed to load bitcode of module "{$name}": {$llvm_err}
diff --git a/compiler/rustc_codegen_llvm/src/declare.rs b/compiler/rustc_codegen_llvm/src/declare.rs
index 981155c35edae..83e3f28d45d68 100644
--- a/compiler/rustc_codegen_llvm/src/declare.rs
+++ b/compiler/rustc_codegen_llvm/src/declare.rs
@@ -176,7 +176,36 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
             signature.fn_ty(),
         );
 
-        if signature.intrinsic().is_none() {
+        if let Some(intrinsic) = signature.intrinsic() {
+            if intrinsic.is_target_specific() {
+                let (llvm_arch, _) = name[5..].split_once('.').unwrap();
+                let target_arch = self.tcx.sess.target.arch.as_ref();
+
+                let is_correct_arch = match llvm_arch {
+                    "aarch64" => matches!(target_arch, "aarch64" | "arm64ec"),
+                    "amdgcn" => target_arch == "amdgpu",
+                    "arm" | "bpf" | "hexagon" => target_arch == llvm_arch,
+                    "loongarch" => matches!(target_arch, "loongarch32" | "loongarch64"),
+                    "mips" => target_arch.starts_with("mips"),
+                    "nvvm" => target_arch == "nvptx64",
+                    "ppc" => matches!(target_arch, "powerpc" | "powerpc64"),
+                    "riscv" => matches!(target_arch, "riscv32" | "riscv64"),
+                    "s390" => target_arch == "s390x",
+                    "spv" => target_arch == "spirv",
+                    "wasm" => matches!(target_arch, "wasm32" | "wasm64"),
+                    "x86" => matches!(target_arch, "x86" | "x86_64"),
+                    _ => true, // fallback for unknown archs
+                };
+
+                if !is_correct_arch {
+                    self.tcx.dcx().emit_fatal(errors::IntrinsicWrongArch {
+                        name,
+                        target_arch,
+                        span: span(),
+                    });
+                }
+            }
+        } else {
             // Don't apply any attributes to intrinsics, they will be applied by AutoUpgrade
             fn_abi.apply_attrs_llfn(self, llfn, instance);
         }
diff --git a/compiler/rustc_codegen_llvm/src/errors.rs b/compiler/rustc_codegen_llvm/src/errors.rs
index 8db8f3160c11b..22d7aeaac9aa0 100644
--- a/compiler/rustc_codegen_llvm/src/errors.rs
+++ b/compiler/rustc_codegen_llvm/src/errors.rs
@@ -157,3 +157,12 @@ pub(crate) struct IntrinsicSignatureMismatch<'a> {
     #[primary_span]
     pub span: Option<Span>,
 }
+
+#[derive(Diagnostic)]
+#[diag(codegen_llvm_intrinsic_wrong_arch)]
+pub(crate) struct IntrinsicWrongArch<'a> {
+    pub name: &'a str,
+    pub target_arch: &'a str,
+    #[primary_span]
+    pub span: Option<Span>,
+}
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index 5d3e382fdc8f3..ee524d91caf9d 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -1139,6 +1139,7 @@ unsafe extern "C" {
         NewFn: &mut Option<&'a Value>,
         CanUpgradeDebugIntrinsicsToRecords: bool,
     ) -> bool;
+    pub(crate) fn LLVMRustIsTargetIntrinsic(ID: NonZero<c_uint>) -> bool;
 
     // Operations on parameters
     pub(crate) fn LLVMIsAArgument(Val: &Value) -> Option<&Value>;
diff --git a/compiler/rustc_codegen_llvm/src/llvm/mod.rs b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
index aa7111474faa5..fedeed8b53c30 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/mod.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/mod.rs
@@ -315,6 +315,10 @@ impl Intrinsic {
         unsafe { LLVMIntrinsicIsOverloaded(self.id).is_true() }
     }
 
+    pub(crate) fn is_target_specific(self) -> bool {
+        unsafe { LLVMRustIsTargetIntrinsic(self.id) }
+    }
+
     pub(crate) fn get_type<'ll>(self, llcx: &'ll Context, type_params: &[&'ll Type]) -> &'ll Type {
         unsafe { LLVMIntrinsicGetType(llcx, self.id, type_params.as_ptr(), type_params.len()) }
     }
diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index 06dcd5d6c3629..c342f8546def3 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -1777,6 +1777,14 @@ LLVMRustUpgradeIntrinsicFunction(LLVMValueRef Fn, LLVMValueRef *NewFn,
   return CanUpgrade;
 }
 
+extern "C" bool LLVMRustIsTargetIntrinsic(unsigned ID) {
+#if LLVM_VERSION_GE(20, 1)
+  return Intrinsic::isTargetIntrinsic(ID);
+#else
+  return Function::isTargetIntrinsic(ID);
+#endif
+}
+
 extern "C" int32_t LLVMRustGetElementTypeArgIndex(LLVMValueRef CallSite) {
   auto *CB = unwrap<CallBase>(CallSite);
   switch (CB->getIntrinsicID()) {
diff --git a/tests/ui/codegen/incorrect-arch-intrinsic.rs b/tests/ui/codegen/incorrect-arch-intrinsic.rs
new file mode 100644
index 0000000000000..b502fb9d7f7b8
--- /dev/null
+++ b/tests/ui/codegen/incorrect-arch-intrinsic.rs
@@ -0,0 +1,17 @@
+//@ build-fail
+//@ ignore-s390x
+//@ normalize-stderr: "target arch `(.*)`" -> "target arch `TARGET_ARCH`"
+
+#![feature(link_llvm_intrinsics, abi_unadjusted)]
+
+extern "unadjusted" {
+    #[link_name = "llvm.s390.sfpc"]
+    fn foo(a: i32);
+    //~^ ERROR: intrinsic `llvm.s390.sfpc` cannot be used with target arch
+}
+
+pub fn main() {
+    unsafe {
+        foo(0);
+    }
+}
diff --git a/tests/ui/codegen/incorrect-arch-intrinsic.stderr b/tests/ui/codegen/incorrect-arch-intrinsic.stderr
new file mode 100644
index 0000000000000..4a11a0bfa8bcb
--- /dev/null
+++ b/tests/ui/codegen/incorrect-arch-intrinsic.stderr
@@ -0,0 +1,8 @@
+error: intrinsic `llvm.s390.sfpc` cannot be used with target arch `TARGET_ARCH`
+  --> $DIR/incorrect-arch-intrinsic.rs:9:5
+   |
+LL |     fn foo(a: i32);
+   |     ^^^^^^^^^^^^^^^
+
+error: aborting due to 1 previous error
+

From 2d549e75cec85ece03d391f41698b76dea54f212 Mon Sep 17 00:00:00 2001
From: sayantn <sayantn05@gmail.com>
Date: Thu, 28 Aug 2025 12:05:03 +0530
Subject: [PATCH 6/7] Add autocast for `i1` vectors

---
 compiler/rustc_codegen_llvm/src/abi.rs     | 39 +++++-----
 compiler/rustc_codegen_llvm/src/builder.rs | 47 +++++++++++++
 tests/codegen-llvm/inject-autocast.rs      | 82 ++++++++++++++++++++++
 3 files changed, 151 insertions(+), 17 deletions(-)
 create mode 100644 tests/codegen-llvm/inject-autocast.rs

diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index f552eca5e21e3..60a886a835cb6 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -369,26 +369,31 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
             return true;
         }
 
-        // Some LLVM intrinsics return **non-packed** structs, but they can't be mimicked from Rust
-        // due to auto field-alignment in non-packed structs (packed structs are represented in LLVM
-        // as, well, packed structs, so they won't match with those either)
-        if self.type_kind(llvm_ty) == TypeKind::Struct
-            && self.type_kind(rust_ty) == TypeKind::Struct
-        {
-            let rust_element_tys = self.struct_element_types(rust_ty);
-            let llvm_element_tys = self.struct_element_types(llvm_ty);
+        match self.type_kind(llvm_ty) {
+            // Some LLVM intrinsics return **non-packed** structs, but they can't be mimicked from Rust
+            // due to auto field-alignment in non-packed structs (packed structs are represented in LLVM
+            // as, well, packed structs, so they won't match with those either)
+            TypeKind::Struct if self.type_kind(rust_ty) == TypeKind::Struct => {
+                let rust_element_tys = self.struct_element_types(rust_ty);
+                let llvm_element_tys = self.struct_element_types(llvm_ty);
+
+                if rust_element_tys.len() != llvm_element_tys.len() {
+                    return false;
+                }
 
-            if rust_element_tys.len() != llvm_element_tys.len() {
-                return false;
+                iter::zip(rust_element_tys, llvm_element_tys).all(
+                    |(rust_element_ty, llvm_element_ty)| {
+                        self.equate_ty(rust_element_ty, llvm_element_ty)
+                    },
+                )
             }
+            TypeKind::Vector if self.element_type(llvm_ty) == self.type_i1() => {
+                let element_count = self.vector_length(llvm_ty) as u64;
+                let int_width = element_count.next_power_of_two().max(8);
 
-            iter::zip(rust_element_tys, llvm_element_tys).all(
-                |(rust_element_ty, llvm_element_ty)| {
-                    self.equate_ty(rust_element_ty, llvm_element_ty)
-                },
-            )
-        } else {
-            false
+                rust_ty == self.type_ix(int_width)
+            }
+            _ => false,
         }
     }
 }
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index e714f216e4749..4a75c25ba51b6 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -1686,6 +1686,46 @@ impl<'a, 'll, CX: Borrow<SCx<'ll>>> GenericBuilder<'a, 'll, CX> {
     }
 }
 impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
+    fn trunc_int_to_i1_vector(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> &'ll Value {
+        let vector_length = self.vector_length(dest_ty) as u64;
+        let int_width = vector_length.next_power_of_two().max(8);
+
+        let bitcasted = self.bitcast(val, self.type_vector(self.type_i1(), int_width));
+        if vector_length == int_width {
+            bitcasted
+        } else {
+            let shuffle_mask =
+                (0..vector_length).map(|i| self.const_i32(i as i32)).collect::<Vec<_>>();
+            self.shuffle_vector(bitcasted, bitcasted, self.const_vector(&shuffle_mask))
+        }
+    }
+
+    fn zext_i1_vector_to_int(
+        &mut self,
+        mut val: &'ll Value,
+        src_ty: &'ll Type,
+        dest_ty: &'ll Type,
+    ) -> &'ll Value {
+        let vector_length = self.vector_length(src_ty) as u64;
+        let int_width = vector_length.next_power_of_two().max(8);
+
+        if vector_length != int_width {
+            let shuffle_indices = match vector_length {
+                0 => unreachable!("zero length vectors are not allowed"),
+                1 => vec![0, 1, 1, 1, 1, 1, 1, 1],
+                2 => vec![0, 1, 2, 3, 2, 3, 2, 3],
+                3 => vec![0, 1, 2, 3, 4, 5, 3, 4],
+                4.. => (0..int_width as i32).collect(),
+            };
+            let shuffle_mask =
+                shuffle_indices.into_iter().map(|i| self.const_i32(i)).collect::<Vec<_>>();
+            val =
+                self.shuffle_vector(val, self.const_null(src_ty), self.const_vector(&shuffle_mask));
+        }
+
+        self.bitcast(val, dest_ty)
+    }
+
     fn autocast(
         &mut self,
         llfn: &'ll Value,
@@ -1714,6 +1754,13 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
                 }
                 ret
             }
+            TypeKind::Vector if self.element_type(llvm_ty) == self.type_i1() => {
+                if is_argument {
+                    self.trunc_int_to_i1_vector(val, dest_ty)
+                } else {
+                    self.zext_i1_vector_to_int(val, src_ty, dest_ty)
+                }
+            }
             _ => unreachable!(),
         }
     }
diff --git a/tests/codegen-llvm/inject-autocast.rs b/tests/codegen-llvm/inject-autocast.rs
new file mode 100644
index 0000000000000..aedc24ef93cab
--- /dev/null
+++ b/tests/codegen-llvm/inject-autocast.rs
@@ -0,0 +1,82 @@
+//@ compile-flags: -C opt-level=0
+//@ only-x86_64
+
+#![feature(link_llvm_intrinsics, abi_unadjusted, repr_simd, simd_ffi, portable_simd, f16)]
+#![crate_type = "lib"]
+
+use std::simd::i64x2;
+
+#[repr(simd)]
+pub struct Tile([i8; 1024]);
+
+#[repr(C, packed)]
+pub struct Bar(u32, i64x2, i64x2, i64x2, i64x2, i64x2, i64x2);
+// CHECK: %Bar = type <{ i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> }>
+
+#[repr(simd)]
+pub struct f16x8([f16; 8]);
+
+// CHECK-LABEL: @struct_with_i1_vector_autocast
+#[no_mangle]
+pub unsafe fn struct_with_i1_vector_autocast(a: i64x2, b: i64x2) -> (u8, u8) {
+    extern "unadjusted" {
+        #[link_name = "llvm.x86.avx512.vp2intersect.q.128"]
+        fn foo(a: i64x2, b: i64x2) -> (u8, u8);
+    }
+
+    // CHECK: [[A:%[0-9]+]] = call { <2 x i1>, <2 x i1> } @llvm.x86.avx512.vp2intersect.q.128(<2 x i64> {{.*}}, <2 x i64> {{.*}})
+    // CHECK: [[B:%[0-9]+]] = extractvalue { <2 x i1>, <2 x i1> } [[A]], 0
+    // CHECK: [[C:%[0-9]+]] = shufflevector <2 x i1> [[B]], <2 x i1> zeroinitializer, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 2, i32 3, i32 2, i32 3>
+    // CHECK: [[D:%[0-9]+]] = bitcast <8 x i1> [[C]] to i8
+    // CHECK: [[E:%[0-9]+]] = insertvalue { i8, i8 } poison, i8 [[D]], 0
+    // CHECK: [[F:%[0-9]+]] = extractvalue { <2 x i1>, <2 x i1> } [[A]], 1
+    // CHECK: [[G:%[0-9]+]] = shufflevector <2 x i1> [[F]], <2 x i1> zeroinitializer, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 2, i32 3, i32 2, i32 3>
+    // CHECK: [[H:%[0-9]+]] = bitcast <8 x i1> [[G]] to i8
+    // CHECK:                 insertvalue { i8, i8 } [[E]], i8 [[H]], 1
+    foo(a, b)
+}
+
+// CHECK-LABEL: @struct_autocast
+#[no_mangle]
+pub unsafe fn struct_autocast(key_metadata: u32, key: i64x2) -> Bar {
+    extern "unadjusted" {
+        #[link_name = "llvm.x86.encodekey128"]
+        fn foo(key_metadata: u32, key: i64x2) -> Bar;
+    }
+
+    // CHECK: [[A:%[0-9]+]] = call { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } @llvm.x86.encodekey128(i32 {{.*}}, <2 x i64> {{.*}})
+    // CHECK: [[B:%[0-9]+]] = extractvalue { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } [[A]], 0
+    // CHECK: [[C:%[0-9]+]] = insertvalue %Bar poison, i32 [[B]], 0
+    // CHECK: [[D:%[0-9]+]] = extractvalue { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } [[A]], 1
+    // CHECK: [[E:%[0-9]+]] = insertvalue %Bar [[C]], <2 x i64> [[D]], 1
+    // CHECK: [[F:%[0-9]+]] = extractvalue { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } [[A]], 2
+    // CHECK: [[G:%[0-9]+]] = insertvalue %Bar [[E]], <2 x i64> [[F]], 2
+    // CHECK: [[H:%[0-9]+]] = extractvalue { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } [[A]], 3
+    // CHECK: [[I:%[0-9]+]] = insertvalue %Bar [[G]], <2 x i64> [[H]], 3
+    // CHECK: [[J:%[0-9]+]] = extractvalue { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } [[A]], 4
+    // CHECK: [[K:%[0-9]+]] = insertvalue %Bar [[I]], <2 x i64> [[J]], 4
+    // CHECK: [[L:%[0-9]+]] = extractvalue { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } [[A]], 5
+    // CHECK: [[M:%[0-9]+]] = insertvalue %Bar [[K]], <2 x i64> [[L]], 5
+    // CHECK: [[N:%[0-9]+]] = extractvalue { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } [[A]], 6
+    // CHECK:                 insertvalue %Bar [[M]], <2 x i64> [[N]], 6
+    foo(key_metadata, key)
+}
+
+// CHECK-LABEL: @i1_vector_autocast
+#[no_mangle]
+pub unsafe fn i1_vector_autocast(a: f16x8) -> u8 {
+    extern "unadjusted" {
+        #[link_name = "llvm.x86.avx512fp16.fpclass.ph.128"]
+        fn foo(a: f16x8, b: i32) -> u8;
+    }
+
+    // CHECK: [[A:%[0-9]+]] = call <8 x i1> @llvm.x86.avx512fp16.fpclass.ph.128(<8 x half> {{.*}}, i32 1)
+    // CHECK: bitcast <8 x i1> [[A]] to i8
+    foo(a, 1)
+}
+
+// CHECK: declare { <2 x i1>, <2 x i1> } @llvm.x86.avx512.vp2intersect.q.128(<2 x i64>, <2 x i64>)
+
+// CHECK: declare { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } @llvm.x86.encodekey128(i32, <2 x i64>)
+
+// CHECK: declare <8 x i1> @llvm.x86.avx512fp16.fpclass.ph.128(<8 x half>, i32 immarg)

From 423d8ece691bc69927b29b7f29fb275707187b11 Mon Sep 17 00:00:00 2001
From: sayantn <sayantn05@gmail.com>
Date: Fri, 30 May 2025 13:10:20 +0530
Subject: [PATCH 7/7] Add autocasts for `bf16` and `bf16xN`

---
 compiler/rustc_codegen_llvm/src/abi.rs      | 15 ++++++++++++---
 compiler/rustc_codegen_llvm/src/builder.rs  |  2 +-
 compiler/rustc_codegen_llvm/src/llvm/ffi.rs |  3 +++
 compiler/rustc_codegen_llvm/src/type_.rs    |  6 +++++-
 tests/codegen-llvm/inject-autocast.rs       | 17 ++++++++++++++++-
 5 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/compiler/rustc_codegen_llvm/src/abi.rs b/compiler/rustc_codegen_llvm/src/abi.rs
index 60a886a835cb6..0368144678944 100644
--- a/compiler/rustc_codegen_llvm/src/abi.rs
+++ b/compiler/rustc_codegen_llvm/src/abi.rs
@@ -370,6 +370,8 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
         }
 
         match self.type_kind(llvm_ty) {
+            TypeKind::BFloat => rust_ty == self.type_i16(),
+
             // Some LLVM intrinsics return **non-packed** structs, but they can't be mimicked from Rust
             // due to auto field-alignment in non-packed structs (packed structs are represented in LLVM
             // as, well, packed structs, so they won't match with those either)
@@ -387,11 +389,18 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
                     },
                 )
             }
-            TypeKind::Vector if self.element_type(llvm_ty) == self.type_i1() => {
+            TypeKind::Vector => {
                 let element_count = self.vector_length(llvm_ty) as u64;
-                let int_width = element_count.next_power_of_two().max(8);
+                let llvm_element_ty = self.element_type(llvm_ty);
 
-                rust_ty == self.type_ix(int_width)
+                if llvm_element_ty == self.type_bf16() {
+                    rust_ty == self.type_vector(self.type_i16(), element_count)
+                } else if llvm_element_ty == self.type_i1() {
+                    let int_width = element_count.next_power_of_two().max(8);
+                    rust_ty == self.type_ix(int_width)
+                } else {
+                    false
+                }
             }
             _ => false,
         }
diff --git a/compiler/rustc_codegen_llvm/src/builder.rs b/compiler/rustc_codegen_llvm/src/builder.rs
index 4a75c25ba51b6..192305afa841c 100644
--- a/compiler/rustc_codegen_llvm/src/builder.rs
+++ b/compiler/rustc_codegen_llvm/src/builder.rs
@@ -1761,7 +1761,7 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
                     self.zext_i1_vector_to_int(val, src_ty, dest_ty)
                 }
             }
-            _ => unreachable!(),
+            _ => self.bitcast(val, dest_ty), // for `bf16(xN)` <-> `u16(xN)`
         }
     }
 
diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
index ee524d91caf9d..e620cd9959100 100644
--- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
+++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs
@@ -963,6 +963,9 @@ unsafe extern "C" {
     pub(crate) fn LLVMDoubleTypeInContext(C: &Context) -> &Type;
     pub(crate) fn LLVMFP128TypeInContext(C: &Context) -> &Type;
 
+    // Operations on non-IEEE real types
+    pub(crate) fn LLVMBFloatTypeInContext(C: &Context) -> &Type;
+
     // Operations on function types
     pub(crate) fn LLVMFunctionType<'a>(
         ReturnType: &'a Type,
diff --git a/compiler/rustc_codegen_llvm/src/type_.rs b/compiler/rustc_codegen_llvm/src/type_.rs
index 371162583a892..f7e3754a82c32 100644
--- a/compiler/rustc_codegen_llvm/src/type_.rs
+++ b/compiler/rustc_codegen_llvm/src/type_.rs
@@ -174,6 +174,10 @@ impl<'ll, CX: Borrow<SCx<'ll>>> GenericCx<'ll, CX> {
             )
         }
     }
+
+    pub(crate) fn type_bf16(&self) -> &'ll Type {
+        unsafe { llvm::LLVMBFloatTypeInContext(self.llcx()) }
+    }
 }
 
 impl<'ll, CX: Borrow<SCx<'ll>>> BaseTypeCodegenMethods for GenericCx<'ll, CX> {
@@ -247,7 +251,7 @@ impl<'ll, CX: Borrow<SCx<'ll>>> BaseTypeCodegenMethods for GenericCx<'ll, CX> {
 
     fn float_width(&self, ty: &'ll Type) -> usize {
         match self.type_kind(ty) {
-            TypeKind::Half => 16,
+            TypeKind::Half | TypeKind::BFloat => 16,
             TypeKind::Float => 32,
             TypeKind::Double => 64,
             TypeKind::X86_FP80 => 80,
diff --git a/tests/codegen-llvm/inject-autocast.rs b/tests/codegen-llvm/inject-autocast.rs
index aedc24ef93cab..d81c67e8a2df9 100644
--- a/tests/codegen-llvm/inject-autocast.rs
+++ b/tests/codegen-llvm/inject-autocast.rs
@@ -4,7 +4,7 @@
 #![feature(link_llvm_intrinsics, abi_unadjusted, repr_simd, simd_ffi, portable_simd, f16)]
 #![crate_type = "lib"]
 
-use std::simd::i64x2;
+use std::simd::{f32x4, i16x8, i64x2};
 
 #[repr(simd)]
 pub struct Tile([i8; 1024]);
@@ -36,6 +36,19 @@ pub unsafe fn struct_with_i1_vector_autocast(a: i64x2, b: i64x2) -> (u8, u8) {
     foo(a, b)
 }
 
+// CHECK-LABEL: @bf16_vector_autocast
+#[no_mangle]
+pub unsafe fn bf16_vector_autocast(a: f32x4) -> i16x8 {
+    extern "unadjusted" {
+        #[link_name = "llvm.x86.vcvtneps2bf16128"]
+        fn foo(a: f32x4) -> i16x8;
+    }
+
+    // CHECK: [[A:%[0-9]+]] = call <8 x bfloat> @llvm.x86.vcvtneps2bf16128(<4 x float> {{.*}})
+    // CHECK: bitcast <8 x bfloat> [[A]] to <8 x i16>
+    foo(a)
+}
+
 // CHECK-LABEL: @struct_autocast
 #[no_mangle]
 pub unsafe fn struct_autocast(key_metadata: u32, key: i64x2) -> Bar {
@@ -77,6 +90,8 @@ pub unsafe fn i1_vector_autocast(a: f16x8) -> u8 {
 
 // CHECK: declare { <2 x i1>, <2 x i1> } @llvm.x86.avx512.vp2intersect.q.128(<2 x i64>, <2 x i64>)
 
+// CHECK: declare <8 x bfloat> @llvm.x86.vcvtneps2bf16128(<4 x float>)
+
 // CHECK: declare { i32, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64>, <2 x i64> } @llvm.x86.encodekey128(i32, <2 x i64>)
 
 // CHECK: declare <8 x i1> @llvm.x86.avx512fp16.fpclass.ph.128(<8 x half>, i32 immarg)