aqjune added inline comments.
================
Comment at: llvm/lib/IR/ConstantFold.cpp:633
// the input constant.
- return UndefValue::get(DestTy);
+ return PoisonValue::get(DestTy);
}
----------------
neildhar wrote:
> spatel wrote:
> > MatzeB wrote:
> > > I believe this is causing some of our clients trouble, especially since
> > > we somehow have a `-fno-strict-float-cast-overflow` flag in clang that
> > > says float->int overflows are not UB... (CC @spatel )
> > I can guess at what the example looks like, but it would be great to have a
> > reduced test.
> > There should be a function attribute in IR corresponding to that clang
> > flag, so we could alter the behavior here based on checking that? Not sure
> > if there's precedence for that kind of transform though.
> Here's a minimal repro for the issue we ran into:
> https://godbolt.org/z/Wdr7q1a9M
Clang is lowering fp-to-int casts into fptosi/ui
(https://godbolt.org/z/Gz3Y7YKKf), but I think in this case clang must emit the
fptosi.sat intrinsic:
https://llvm.org/docs/LangRef.html#llvm-fptosi-sat-intrinsic
It guarantees that the result is well-defined.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D92270/new/
https://reviews.llvm.org/D92270
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