sepavloff added inline comments.
================
Comment at: clang/include/clang/Basic/LangOptions.h:622
setFPContractMode(LangOptions::FPM_Off);
setRoundingMode(static_cast<RoundingMode>(LangOptions::FPR_ToNearest));
setFPExceptionMode(LangOptions::FPE_Ignore);
----------------
efriedma wrote:
> sepavloff wrote:
> > efriedma wrote:
> > > I'm suggesting this should be
> > > `setRoundingMode(llvm::RoundingMode::Dynamic)`.
> > >
> > > If FENV_ACCESS is off, getEffectiveRoundingMode() converts that to
> > > "nearest". If FENV_ACCESS is turned on, the mode is treated as dynamic.
> > > This is exactly what we want.
> > It would change semantics. In particular, it would make impossible to use
> > FP arithmetic in constexpr functions. An expression like `1.0 / 3.0` cannot
> > be evaluated with dynamic rounding mode.
> Can we just change the relevant code in ExprConstant to call
> getEffectiveRoundingMode()?
What is the advantage of using FE_DYNAMIC in the case when it is known that
rounding mode is FE_TONEAREST?
Probably `FENV_ROUND FE_DYNAMIC` should result in `dynamic` rounding even if
`FENV_ACCESS ON` is absent. Rounding mode cannot be changed in this case but it
can be used to inform the compiler that such function can be called in
environment, where rounding mode is non-default. It would prevent some constant
evaluations and other transformations that assume rounding mode is known.
Anyway the standard only allow to assume FE_TONEAREST but does not require this.
In such case `getEffectiveRoundingMode` is not needed.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D126364/new/
https://reviews.llvm.org/D126364
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