Fix PR2553

llvm-svn: 53715

llvm/lib/Transforms/Scalar/InstructionCombining.cpp

@@ -2255,7 +2255,8 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
 Instruction *InstCombiner::visitSub(BinaryOperator &I) {
   Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
 
-  if (Op0 == Op1)         // sub X, X  -> 0
+  if (Op0 == Op1 &&                        // sub X, X  -> 0
+      !I.getType()->isFPOrFPVector())
     return ReplaceInstUsesWith(I, Constant::getNullValue(I.getType()));
 
   // If this is a 'B = x-(-A)', change to B = x+A...

llvm/test/Transforms/InstCombine/2008-07-16-fsub.ll

@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep sub
+; PR2553
+
+define double @test(double %X) nounwind {
+	; fsub of self can't be optimized away.
+	%Y = sub double %X, %X
+	ret double %Y
+}