[PATCH] D131873: [PowerPC] Optimize compare by using record form in post-RA.

Wed Oct 26 20:07:22 PDT 2022

Esme added a comment.

In D131873#3881526 <https://reviews.llvm.org/D131873#3881526>, @shchenz wrote:

> Compared with previous versions, to me, seems some valid transformations are gone now because of the new bail out case `Subtarget.isPPC64() && Opc == PPC::CMPWI`. Maybe we can have a further check why PPC64 generates `CMPWI 0` for some cases. For these cases, I guess `CMPDI 0` should also be ok, so that there will be more record form opportunities here. But we can do that in another patch.

Currently PPC64 generates `CMPWI 0` for int32 operands, which is reasonable.
`CMPDI 0` will be ok if the use of the comparison is an equality check, however it's not easy to find the reliable use in Post-RA.
More investigation is required to exploit other opportunities for optimization comparison.

================
Comment at: llvm/lib/Target/PowerPC/PPCInstrInfo.cpp:2839
+  if (SrcRegHasOtherUse || CmpMI.getOperand(1).isKill())
+    fixupIsDeadOrKill(SrcMI, &CmpMI, SrcReg);
+
----------------
shchenz wrote:
> hmm, another caller of `fixupIsDeadOrKill()`, we refactor this in D133103. FYI @nemanjai 
D133103 seems in progress, so this patch will not be rebase on it. Maybe D133103 can refactor this after this patch lands.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D131873/new/

https://reviews.llvm.org/D131873