[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

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.

llvm/test/CodeGen/PowerPC/eliminate-compare-of-copy.ll

@@ -0,0 +1,29 @@
+; RUN: llc -verify-machineinstrs -mtriple=powerpc64le-unknown-linux-gnu \
+; RUN:   -mcpu=pwr8 -ppc-asm-full-reg-names < %s | FileCheck %s
+
+define dso_local signext i32 @func(i32 zeroext %x, i32 zeroext %y) local_unnamed_addr {
+; CHECK-LABEL: func
+; CHECK: or. {{r[0-9]+}}, r4, r3
+; CHECK-NOT: cmplwi
+; CHECK: blr
+entry:
+  %or = or i32 %y, %x
+  %tobool = icmp eq i32 %or, 0
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  %call = tail call signext i32 bitcast (i32 (...)* @f1 to i32 ()*)()
+  br label %return
+
+if.else:                                          ; preds = %entry
+  %call1 = tail call signext i32 bitcast (i32 (...)* @f2 to i32 ()*)()
+  br label %return
+
+return:                                           ; preds = %if.else, %if.then
+  %retval.0 = phi i32 [ %call, %if.then ], [ %call1, %if.else ]
+  ret i32 %retval.0
+}
+
+declare signext i32 @f1(...) local_unnamed_addr
+
+declare signext i32 @f2(...) local_unnamed_addr