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Don't use switch fallthrough #423

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Don't use switch fallthrough #423

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f624aa8
Don't use switch fallthrough
llvm-beanz Sep 2, 2025
706b13e
Fix comments and don't truncate buffers
llvm-beanz Sep 2, 2025
1a4c00f
Bleh
llvm-beanz Sep 3, 2025
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14 changes: 5 additions & 9 deletions test/Feature/WaveOps/WaveActiveAnyTrue.test
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Original file line number Diff line number Diff line change
Expand Up @@ -5,15 +5,11 @@ RWStructuredBuffer<uint> Out : register(u1);
[numthreads(4, 1, 1)]
void main(uint3 threadID : SV_DispatchThreadID) {
bool B1 = false;
switch (value[threadID.x]) {
case 0:
case 2: // threads 0, 1, 2; result for each false
Out[threadID.x] = WaveActiveAnyTrue(B1);
B1 = true;
break;
default: // thread 3; result is false
Out[threadID.x] = WaveActiveAnyTrue(B1);
break;
if (value[threadID.x] == 0 || value[threadID.x] == 2) {
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While this matches the behavior of the replaced switch, the comment seemed to imply that thread 1 was meant to also go through this branch. The later comment also seems to assume this ("result for all threads is true because B1 is true for threads 0-2"). However thread numbers are translated through the LUT value, which is [0, 0, 1, 2].

Even accounting for this looked up value, the removed and remaining comments don't seem to align with the test's design and expected behavior. The test seems to be written in a way to make it a bit confusing on purpose.

I don't understand the intention behind these odd details of the test. Was this a mistake in the code or in the comments?

It would be nice to have an explanatory comment for the test design.

The second test has a similar issue.

Out[threadID.x] = WaveActiveAnyTrue(B1);
B1 = true;
} else {
Out[threadID.x] = WaveActiveAnyTrue(B1);
}
// result for all threads is true because B1 is true for threads 0-2
Out[threadID.x + 4] = WaveActiveAnyTrue(B1);
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25 changes: 12 additions & 13 deletions test/Feature/WaveOps/WaveActiveCountBits.test
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Original file line number Diff line number Diff line change
Expand Up @@ -6,17 +6,16 @@ RWStructuredBuffer<uint> Out : register(u1);
void main(uint3 threadID : SV_DispatchThreadID) {
bool B1 = false;

switch (value[threadID.x]) {
case 0: // threads 0 and 1; result is number of active lanes (2)
Out[threadID.x + 4] = WaveActiveCountBits(true); // threads 0 and 1
case 2:
B1 = true; // set b1 to true for thread 3
break;
default:
Out[threadID.x + 4] = WaveActiveCountBits(false); // thread 2; expect 0
break;
}
// should be 3 because B1 set to true for threads 0,1, and 3.
if (value[threadID.x] == 0) // thread 0 and 1.
Out[threadID.x + 4] = WaveActiveCountBits(true);
// thread 0-3 set b1 to true.
if (value[threadID.x] == 0 || value[threadID.x] == 1)
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Note: This isn't equivalent to the original behavior. == 1 should be == 2 for equivalent behavior.

B1 = true;
else // thread 4
Out[threadID.x + 4] = WaveActiveCountBits(false);

// Out[threadID.x + 4] on thread 3 is never written to and should remain 0.
// All threads count 3 because B1 set to true for threads 0,1, and 3.
uint Count = WaveActiveCountBits(B1);
Out[threadID.x] = Count;
}
Expand All @@ -35,11 +34,11 @@ Buffers:
- Name: Out
Format: UInt32
Stride: 4
ZeroInitSize: 28
ZeroInitSize: 32
- Name: ExpectedOut
Format: UInt32
Stride: 4
Data: [3, 3, 3, 3, 2, 2, 0]
Data: [3, 3, 3, 3, 2, 2, 0, 0]
Results:
- Result: Test
Rule: BufferExact
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