[PATCH] D136786: Fix `unsafe-fp-math` attribute emission.

[Michele Scandale via Phabricator via cfe-commits]

michele.scandale added inline comments.


================
Comment at: clang/lib/CodeGen/CGCall.cpp:1865
       FuncAttrs.addAttribute("approx-func-fp-math", "true");
-    if ((LangOpts.FastMath ||
-         (!LangOpts.FastMath && LangOpts.AllowFPReassoc &&
-          LangOpts.AllowRecip && !LangOpts.FiniteMathOnly &&
-          LangOpts.NoSignedZero && LangOpts.ApproxFunc)) &&
-        LangOpts.getDefaultFPContractMode() != LangOptions::FPModeKind::FPM_Off)
+    if (LangOpts.UnsafeFPMath &&
+        (LangOpts.getDefaultFPContractMode() ==
----------------
michele.scandale wrote:
> I've found quite confusing the `(FastMath || (!FastMath && ... ))`.
> 
> Using directly `UnsafeFPMath` seems more compact, however it also causes to taking into account the value for `MathErrno` -- which it might be not relevant.
> 
> If `MathErrno` shouldn't affect this, then I would rewrite this as:
> ```
> if (LangOpts.AllowFPReassoc && LangOpts.AllowRecip &&
>      LangOpts.NoSignedZero && LangOpts.ApproxFunc &&
>      (LangOpts.getDefaultFPContractMode() ==
>          LangOptions::FPModeKind::FPM_Fast ||
>      LangOpts.getDefaultFPContractMode() ==
>          LangOptions::FPModeKind::FPM_FastHonorPragmas))
>   FuncAttrs.addAttribute("unsafe-fp-math", "true");
> ```
> so that only the relevant options are considered and there is no need to think about what is implied by `FastMath`.
I do wonder if in https://github.com/llvm/llvm-project/blob/main/clang/lib/Driver/ToolChains/Clang.cpp#L3089-L3091 is actually correct to have `!MathErrno`. In the GCC documentation of `-funsafe-math-optimizations` I don't see any connection to the `-fmath-errno` or `-fno-math-errno` options.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D136786/new/

https://reviews.llvm.org/D136786