| Issue |
145752
|
| Summary |
[HLSL][DirectX] `firstbithigh` returns bit index from wrong side
|
| Labels |
HLSL
|
| Assignees |
|
| Reporter |
V-FEXrt
|
https://godbolt.org/z/1ahzc64a8
DXC returns `32 - firstbit(S)hi` instead of directly returning `firstbit(S)hi` like clang currently does. This test confirms it is intentional https://github.com/microsoft/DirectXShaderCompiler/blob/b390fb19adc5d7c23180eb470470411fce986910/tools/clang/test/HLSLFileCheck/hlsl/intrinsics/bitwise/firstbitHi.hlsl#L10
Without the inversion the result has the bit set from the wrong direction.
This is a bug in the clang lowering that was caught by https://github.com/llvm/offload-test-suite/pull/210
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