PR for llvm/llvm-project#66984 #706
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(cherry picked from commit 8b4e29b35d21b079e8b30244cbbfc4d4bc4a29d4)
The write to the SEH catch object happens before cleanuppads are executed, while the first reference to the object will typically be in a catchpad. If we make use of first-use analysis, we may end up allocating an alloca used inside the cleanuppad and the catch object at the same stack offset, which would be incorrect. https://reviews.llvm.org/D86673 was a previous attempt to fix it. It used the heuristic "a slot loaded in a WinEH pad and never written" to detect catch objects. However, because it checks for more than one load (while probably more than zero was intended), the fix does not actually work. The general approach also seems dubious to me, so this patch reverts that change entirely, and instead marks all catch object slots as conservative (i.e. excluded from first-use analysis) based on the WinEHFuncInfo. As far as I can tell we don't need any heuristics here, we know exactly which slots are affected. Fixes llvm/llvm-project#66984. (cherry picked from commit b3cb4f069c2cb99bdae68d6906156af20e76314f)
This is a followup to #66988. The implementation there did not account for the possibility of the catch object frame index referrring to a fixed object, which is the case on win64. (cherry picked from commit aa70f4d8cf8f09a2997773156289b16d6a16ec01)
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@nikic should we merge this into 17.0.1? |
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Yeah, this fixes a miscompile seen in the wild. |
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resolves llvm/llvm-project#66984