[X86] Don't invert NewCC variable while processing the jcc/setcc/cmovcc instructions in optimizeCompareInstr.

The NewCC variable is calculated outside of the loop that processes jcc/setcc/cmovcc instructions. If we invert it during the loop it can cause an incorrect value to be used by a later iteration. Instead only read it during the loop and use a new variable to store the possibly inverted value.

Fixes PR35399.

llvm-svn: 318934

1 files changed, 9 insertions, 7 deletions

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 68f964cc866..bd8d447fb88 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -7475,6 +7475,7 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, unsigned SrcReg,
       }
       if (OldCC == X86::COND_INVALID) return false;
     }
+    X86::CondCode ReplacementCC = X86::COND_INVALID;
     if (IsCmpZero) {
       switch (OldCC) {
       default: break;
@@ -7494,31 +7495,32 @@ bool X86InstrInfo::optimizeCompareInstr(MachineInstr &CmpInstr, unsigned SrcReg,
         default:
           return false;
         case X86::COND_E:
+          ReplacementCC = NewCC;
           break;
         case X86::COND_NE:
-          NewCC = GetOppositeBranchCondition(NewCC);
+          ReplacementCC = GetOppositeBranchCondition(NewCC);
           break;
         }
     } else if (IsSwapped) {
       // If we have SUB(r1, r2) and CMP(r2, r1), the condition code needs
       // to be changed from r2 > r1 to r1 < r2, from r2 < r1 to r1 > r2, etc.
       // We swap the condition code and synthesize the new opcode.
-      NewCC = getSwappedCondition(OldCC);
-      if (NewCC == X86::COND_INVALID) return false;
+      ReplacementCC = getSwappedCondition(OldCC);
+      if (ReplacementCC == X86::COND_INVALID) return false;
     }
 
-    if ((ShouldUpdateCC || IsSwapped) && NewCC != OldCC) {
+    if ((ShouldUpdateCC || IsSwapped) && ReplacementCC != OldCC) {
       // Synthesize the new opcode.
       bool HasMemoryOperand = Instr.hasOneMemOperand();
       unsigned NewOpc;
       if (Instr.isBranch())
-        NewOpc = GetCondBranchFromCond(NewCC);
+        NewOpc = GetCondBranchFromCond(ReplacementCC);
       else if(OpcIsSET)
-        NewOpc = getSETFromCond(NewCC, HasMemoryOperand);
+        NewOpc = getSETFromCond(ReplacementCC, HasMemoryOperand);
       else {
         unsigned DstReg = Instr.getOperand(0).getReg();
         const TargetRegisterClass *DstRC = MRI->getRegClass(DstReg);
-        NewOpc = getCMovFromCond(NewCC, TRI->getRegSizeInBits(*DstRC)/8,
+        NewOpc = getCMovFromCond(ReplacementCC, TRI->getRegSizeInBits(*DstRC)/8,
                                  HasMemoryOperand);
       }