zahiraam 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:
> 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.
Interesting! Using on the command line 'funsafe-math-optimization' implies 'math-errno'. But 'funsafe-math-optimizations' is triggered when this is true:
!MathErrno && AssociativeMath && ReciprocalMath && !SignedZeros && ApproxFunc && !TrappingMath
See here: https://github.com/llvm/llvm-project/blob/main/clang/lib/Driver/ToolChains/Clang.cpp#L3089
================
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() ==
----------------
zahiraam wrote:
> michele.scandale wrote:
> > 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.
> Interesting! Using on the command line 'funsafe-math-optimization' implies 'math-errno'. But 'funsafe-math-optimizations' is triggered when this is true:
> !MathErrno && AssociativeMath && ReciprocalMath && !SignedZeros && ApproxFunc && !TrappingMath
>
> See here: https://github.com/llvm/llvm-project/blob/main/clang/lib/Driver/ToolChains/Clang.cpp#L3089
When the ‘funsafe-math-optimizations’ is used on the command line LangOpts.UnsafeFP is ‘0’.
The function attribute ‘funnsafe-fp-math’ is not set. Is that what’s wanted? I would have thought that we want the attribute enabled for unsafe mode.
If we call
SpecialOperations = AllowFPReassoc && NoSignedZero && AllowRecip && ApproxFunc && !RoundingMath.
‘ffast-math’ = !MathErrno && FiniteMathOnly && SpecialOperations
‘funsafe-math-optimizations’ = MathErrno && !FiniteMathOnly && SpecialOperations
(it's true that there is no mention of MathErrno in the GCC doc, but the default is fmath-errno so presumably using this option on the command line implies MathErrno).
The function attribute UnsafeFPMath is enabled for
(‘ffast-math’ || ‘funsafe-math-optimization’).
That will lead to this condition:
(SpecialOperations && MathErrNo && "-ffast-math" && -ffp-contract=fast") || (SpecialOperations && "-fmath-errno" && "-ffp-contract=on") .
Repository:
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https://reviews.llvm.org/D136786/new/
https://reviews.llvm.org/D136786