Speed up single-value SearchValues<string> candidate verification

src/coreclr/System.Private.CoreLib/src/System/String.CoreCLR.cs

@@ -38,7 +38,7 @@ internal static unsafe void InternalCopy(string src, IntPtr dest, int len)
         {
             if (len != 0)
             {
-                SpanHelpers.Memmove(ref *(byte*)dest, ref Unsafe.As<char, byte>(ref src.GetRawStringData()), (nuint)len);
+                SpanHelpers.Memmove(ref *(byte*)dest, ref src.GetRawStringDataAsUInt8(), (nuint)len);
             }
         }
 

src/libraries/Fuzzing/DotnetFuzzing/Fuzzers/SearchValuesStringFuzzer.cs

@@ -36,8 +36,8 @@ private static void Test(ReadOnlySpan<char> haystack, ReadOnlySpan<char> haystac
         SearchValues<string> searchValues = SearchValues.Create(needles, comparisonType);
 
         int index = haystack.IndexOfAny(searchValues);
-        Assert.Equal(index, haystackCopy.IndexOfAny(searchValues));
-        Assert.Equal(index, IndexOfAnyReferenceImpl(haystack, needles, comparisonType));
+        AssertEqual(index, haystackCopy.IndexOfAny(searchValues), searchValues);
+        AssertEqual(index, IndexOfAnyReferenceImpl(haystack, needles, comparisonType), searchValues);
     }
 
     private static int IndexOfAnyReferenceImpl(ReadOnlySpan<char> haystack, string[] needles, StringComparison comparisonType)
@@ -55,4 +55,15 @@ private static int IndexOfAnyReferenceImpl(ReadOnlySpan<char> haystack, string[]
 
         return minIndex == int.MaxValue ? -1 : minIndex;
     }
+
+    private static void AssertEqual(int expected, int actual, SearchValues<string> searchValues)
+    {
+        if (expected != actual)
+        {
+            Type implType = searchValues.GetType();
+            string impl = $"{implType.Name} [{string.Join(", ", implType.GenericTypeArguments.Select(t => t.Name))}]";
+
+            throw new Exception($"Expected {expected}, got {actual} for impl='{impl}'");
+        }
+    }
 }

src/libraries/System.Memory/tests/Span/StringSearchValues.cs

@@ -7,6 +7,7 @@
 using System.Linq;
 using System.Runtime.ExceptionServices;
 using System.Runtime.InteropServices;
+using System.Runtime.Intrinsics.X86;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.DotNet.RemoteExecutor;
@@ -313,6 +314,7 @@ public static void IndexOfAny_InvalidUtf16()
             IndexOfAny(StringComparison.OrdinalIgnoreCase, -1, " foO\uD801bar", "oo\uD800baR, bar\uD800foo");
 
             // Low surrogate without the high surrogate.
+            IndexOfAny(StringComparison.OrdinalIgnoreCase, 1, "\uD801\uDCD8\uD8FB\uDCD8", "\uDCD8");
             IndexOfAny(StringComparison.OrdinalIgnoreCase, 1, "\uD801\uDCD8\uD8FB\uDCD8", "foo, \uDCD8");
         }
 
@@ -337,6 +339,15 @@ public static void IndexOfAny_InvalidUtf16()
         [InlineData("abcd!")]
         [InlineData("abcdefgh")]
         [InlineData("abcdefghi")]
+        [InlineData("123456789")]
+        [InlineData("123456789a")]
+        [InlineData("123456789ab")]
+        [InlineData("123456789abc")]
+        [InlineData("123456789abcd")]
+        [InlineData("123456789abcde")]
+        [InlineData("123456789abcdef")]
+        [InlineData("123456789abcdefg")]
+        [InlineData("123456789abcdefgh")]
         // Multiple values, but they all share the same prefix
         [InlineData("abc", "ab", "abcd")]
         // These should hit the Aho-Corasick implementation
@@ -406,9 +417,25 @@ static void TestCore(string[] valuesArray)
                 Values_ImplementsSearchValuesBase(StringComparison.OrdinalIgnoreCase, valuesArray);
 
                 string values = string.Join(", ", valuesArray);
+                string text = valuesArray[0];
 
-                IndexOfAny(StringComparison.Ordinal, 0, valuesArray[0], values);
-                IndexOfAny(StringComparison.OrdinalIgnoreCase, 0, valuesArray[0], values);
+                IndexOfAny(StringComparison.Ordinal, 0, text, values);
+                IndexOfAny(StringComparison.OrdinalIgnoreCase, 0, text, values);
+
+                // Replace every position in the text with a different character.
+                foreach (StringComparison comparisonType in new[] { StringComparison.Ordinal, StringComparison.OrdinalIgnoreCase })
+                {
+                    SearchValues<string> stringValues = SearchValues.Create(valuesArray, comparisonType);
+
+                    for (int i = 0; i < text.Length - 1; i++)
+                    {
+                        foreach (char replacement in "AaBb _!\u00F6")
+                        {
+                            string newText = $"{text.AsSpan(0, i)}{replacement}{text.AsSpan(i + 1)}";
+                            Assert.Equal(IndexOfAnyReferenceImpl(newText, valuesArray, comparisonType), newText.IndexOfAny(stringValues));
+                        }
+                    }
+                }
             }
         }
 
@@ -499,6 +526,20 @@ public static void TestIndexOfAny_RandomInputs_Stress()
         {
             RunStress();
 
+            if (RemoteExecutor.IsSupported && Avx512F.IsSupported)
+            {
+                var psi = new ProcessStartInfo();
+                psi.Environment.Add("DOTNET_EnableAVX512F", "0");
+                RemoteExecutor.Invoke(RunStress, new RemoteInvokeOptions { StartInfo = psi, TimeOut = 10 * 60 * 1000 }).Dispose();
+            }
+
+            if (RemoteExecutor.IsSupported && Avx2.IsSupported)
+            {
+                var psi = new ProcessStartInfo();
+                psi.Environment.Add("DOTNET_EnableAVX2", "0");
+                RemoteExecutor.Invoke(RunStress, new RemoteInvokeOptions { StartInfo = psi, TimeOut = 10 * 60 * 1000 }).Dispose();
+            }
+
             if (CanTestInvariantCulture)
             {
                 RunUsingInvariantCulture(static () => RunStress());

src/libraries/System.Private.CoreLib/src/System/Collections/Generic/RandomizedStringEqualityComparer.cs

@@ -80,7 +80,7 @@ public override int GetHashCode(string? obj)
                 // The Ordinal version of Marvin32 operates over bytes.
                 // The multiplication from # chars -> # bytes will never integer overflow.
                 return Marvin.ComputeHash32(
-                    ref Unsafe.As<char, byte>(ref obj.GetRawStringData()),
+                    ref obj.GetRawStringDataAsUInt8(),
                     (uint)obj.Length * 2,
                     _seed.p0, _seed.p1);
             }