[PATCH] D66329: [PowerPC] [Peephole] fold frame offset by using index form to save add.

[ChenZheng via Phabricator via llvm-commits]

shchenz created this revision.
shchenz added reviewers: jsji, hfinkel, nemanjai, qshanz.
Herald added subscribers: llvm-commits, wuzish, arphaman, MaskRay, kosarev, kbarton, hiraditya.
Herald added a project: LLVM.
shchenz edited reviewers, added: steven.zhang; removed: qshanz.

Before pass PEI, all stack variables has a placeholder 0 as its offset to frame base. And in pass PEI, the real offset is filled. Like:

Before `PEI`:

  renamable $x6 = ADDI8 %stack.0, 0
  renamable $x6 = ADD8 killed renamable $x6, renamable $x5
  STW killed renamable $r3, 4, killed renamable $x6 :: (store 4 into %ir.14, !tbaa !2)

after `PEI`:

  renamable $x6 = ADDI8 $x1, -80      ;;; 0 is replaced with -80
  renamable $x6 = ADD8 killed renamable $x6, renamable $x5
  STW killed renamable $r3, 4, killed renamable $x6 :: (store 4 into %ir.14, !tbaa !2)

After PEI there is a peephole opt opportunity to combine above -80 in `ADDI8` with 4 in the `STW` to eliminate unnecessary `ADD8`.

So for above case, optimized instruction should be like:

  renamable $x6 = ADDI8 $x1, -76
  STWX killed renamable $r3, renamable $x5, killed renamable $x6 :: (store 4 into %ir.6, !tbaa !2)

This patch is to implement such peephole opt.


https://reviews.llvm.org/D66329

Files:
  llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
  llvm/lib/Target/PowerPC/PPCInstrInfo.h
  llvm/lib/Target/PowerPC/PPCPreEmitPeephole.cpp
  llvm/lib/Target/PowerPC/PPCRegisterInfo.h
  llvm/test/CodeGen/PowerPC/fold-frame-offset-using-rr.mir

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