jsji accepted this revision.
jsji added a comment.
This revision is now accepted and ready to land.
LGTM. Thanks for investigating GCC behavior.
================
Comment at: clang/lib/Basic/Targets/PPC.h:211
+ case 's': // VSX vector register to hold scalar double data
+ case 'w': // VSX vector register to hold scalar double data
case 'a': // Any VSX register
----------------
MaskRay wrote:
> jsji wrote:
> > Add some more comments for `w` to distinguish it from `s`?
> >
> > Do we want to keep compatibility with GCC?
> > According to
> > https://gcc.gnu.org/onlinedocs/gcc-9.1.0/gcc/Machine-Constraints.html#Machine-Constraints,
> >
> > `ww` is `FP or VSX register to perform float operations under -mvsx or
> > NO_REGS.`,
> > while `ws` is `VSX vector register to hold scalar double values `.
> >
> > So `ww` can use `FP` while `ws` can NOT ?
> I played with "ws" and "ww" but can't find any behavior difference from
> assembly produced by powerpc64le-linux-gnu-gcc. I'll keep the current form
> (which is known to make musl fmax/fmaxf build) unless the gcc semantics are
> clearer.
OK. Thanks. So maybe it is just the misleading doc problem of GCC.
================
Comment at: llvm/lib/Target/PowerPC/PPCISelLowering.cpp:14080
return std::make_pair(0U, &PPC::VSRCRegClass);
- } else if (Constraint == "ws" && Subtarget.hasVSX()) {
+ } else if ((Constraint == "ws" || Constraint == "ww") && Subtarget.hasVSX())
{
if (VT == MVT::f32 && Subtarget.hasP8Vector())
----------------
MaskRay wrote:
> jsji wrote:
> > Should we exclude `FP` for `ws` and return `VFRCRegClass` instead of
> > `VSFRCRegClass` ?
> Can you elaborate on what I should do? I'm not familiar with the register
> info stuff...
`VSFRC` contains both `F8RC` and `VFRC`. `F8RC` is FP.
So if `ws` can NOT use FP, then we should not use `VSFRC`.
However, if `ws` can use `FP` as well as you found in later GCC experiments,
then we don't need to do this.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D64119/new/
https://reviews.llvm.org/D64119
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