Fix PR4485.

Avoid unnecessary duplication of operand 0 of X86::FpSET_ST0_80. This duplication would
cause one register to remain on the stack at the function return.

llvm-svn: 74534

1 files changed, 6 insertions, 3 deletions

diff --git a/llvm/lib/Target/X86/X86FloatingPoint.cpp b/llvm/lib/Target/X86/X86FloatingPoint.cpp
index c282dc00947..37027ee8beb 100644
--- a/llvm/lib/Target/X86/X86FloatingPoint.cpp
+++ b/llvm/lib/Target/X86/X86FloatingPoint.cpp
@@ -991,13 +991,16 @@ void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
   case X86::FpSET_ST0_32:
   case X86::FpSET_ST0_64:
   case X86::FpSET_ST0_80: {
-    unsigned RegOnTop = getStackEntry(0);
+    unsigned Op0 = getFPReg(MI->getOperand(0));
+
     // FpSET_ST0_80 is generated by copyRegToReg for both function return
     // and inline assembly with the "st" constrain. In the latter case,
     // it is possible for ST(0) to be alive after this instruction.
-    if (!MI->killsRegister(X86::FP0 + RegOnTop)) {
-      // Duplicate ST0
+    if (!MI->killsRegister(X86::FP0 + Op0)) {
+      // Duplicate Op0
       duplicateToTop(0, 7 /*temp register*/, I);
+    } else {
+      moveToTop(Op0, I);
     }
     --StackTop;   // "Forget" we have something on the top of stack!
     break;