[mono] Workaround MSVC miscompiling sgen_clz #114786
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After the recent VS upgrade from 17.12.5 to 17.13.2 we started seeing access violations in the mono-aot-cross.exe when targetting wasm. We tracked it down to sgen_clz being miscompiled, we can workaround the compiler bug by switching from ternary condition to if/else.
akoeplinger
requested review from
BrzVlad,
steveisok and
vitek-karas
as code owners
| @@ -60,7 +60,10 @@ static inline guint32 | |||
| sgen_clz (guint32 x) | |||
| { | |||
| gulong leading_zero_bits; | |||
| return _BitScanReverse (&leading_zero_bits, (gulong)x) ? 31 - leading_zero_bits : 32; | |||
| if (_BitScanReverse (&leading_zero_bits, (gulong)x)) | |||
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Consider adding an inline comment above this if/else block to explain that the change is a workaround for the MSVC miscompilation issue encountered in VS 17.13.2.
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lewing
approved these changes
Apr 17, 2025
steveisok
approved these changes
Apr 17, 2025
jkoritzinsky
approved these changes
Apr 17, 2025
|
/ba-g CI is blocked due to other issues but this is a no-op change so merging to unblock the runtime -> sdk flow |
This was referenced Apr 17, 2025
Open
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/backport to release/9.0-staging |
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/backport to release/8.0-staging |
|
Started backporting to release/9.0-staging: https://github.com/dotnet/runtime/actions/runs/14593713790 |
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Started backporting to release/8.0-staging: https://github.com/dotnet/runtime/actions/runs/14593716274 |
This was referenced Apr 22, 2025
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After the recent VS upgrade from 17.12.5 to 17.13.2 we started seeing access violations in the mono-aot-cross.exe when targetting wasm.
We tracked it down to sgen_clz being miscompiled, we can workaround the compiler bug by switching from ternary condition to if/else.
Thanks to @lateralusX for the great help :)