Fix PR4185.

Handle FpSET_ST0_80 being used when ST0 is still alive.

llvm-svn: 73850

llvm/lib/Target/X86/X86FloatingPoint.cpp

@@ -991,8 +991,13 @@ void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
   case X86::FpSET_ST0_32:
   case X86::FpSET_ST0_64:
   case X86::FpSET_ST0_80:
-    assert((StackTop == 1 || StackTop == 2)
-           && "Stack should have one or two element on it to return!");
+    // 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 FP0 to be alive after this instruction.
+    if (!MI->killsRegister(X86::FP0)) {
+      // Duplicate ST0
+      duplicateToTop(0, 0, I);
+    }
     --StackTop;   // "Forget" we have something on the top of stack!
     break;
   case X86::FpSET_ST1_32:

llvm/test/CodeGen/X86/inline-asm-fpstack2.ll

@@ -0,0 +1,10 @@
+; RUN: llvm-as < %s | llc -march=x86 > %t
+; RUN: grep {fld	%%st(0)} %t
+; PR4185
+
+define void @test() {
+return:
+	call void asm sideeffect "fistpl $0", "{st}"(double 1.000000e+06)
+	call void asm sideeffect "fistpl $0", "{st}"(double 1.000000e+06)
+	ret void
+}