[PowerPC] Look through copies for compare elimination

We currently miss the opportunities for optmizing comparisons in the peephole
optimizer if the input is the result of a COPY since we look for record-form
versions of the producing instruction.

This patch simply lets the optimization peek through copies.

Differential revision: https://reviews.llvm.org/D59633

llvm-svn: 362438

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
index cacbe4eecc5..0799c4281e3 100644
--- a/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
+++ b/llvm/lib/Target/PowerPC/PPCInstrInfo.cpp
@@ -1653,6 +1653,7 @@ bool PPCInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, unsigned SrcReg,
   if (OpC == PPC::FCMPUS || OpC == PPC::FCMPUD)
     return false;
 
+  const TargetRegisterInfo *TRI = &getRegisterInfo();
   // The record forms set the condition register based on a signed comparison
   // with zero (so says the ISA manual). This is not as straightforward as it
   // seems, however, because this is always a 64-bit comparison on PPC64, even
@@ -1666,6 +1667,11 @@ bool PPCInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, unsigned SrcReg,
   bool is32BitUnsignedCompare = OpC == PPC::CMPLWI || OpC == PPC::CMPLW;
   bool is64BitUnsignedCompare = OpC == PPC::CMPLDI || OpC == PPC::CMPLD;
 
+  // Look through copies unless that gets us to a physical register.
+  unsigned ActualSrc = TRI->lookThruCopyLike(SrcReg, MRI);
+  if (TargetRegisterInfo::isVirtualRegister(ActualSrc))
+    SrcReg = ActualSrc;
+
   // Get the unique definition of SrcReg.
   MachineInstr *MI = MRI->getUniqueVRegDef(SrcReg);
   if (!MI) return false;
@@ -1794,7 +1800,6 @@ bool PPCInstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, unsigned SrcReg,
   }
 
   // Search for Sub.
-  const TargetRegisterInfo *TRI = &getRegisterInfo();
   --I;
 
   // Get ready to iterate backward from CmpInstr.