Don't do (x - (y - z)) --> (x + (z - y)) on floating-point types, because

it may round differently. This fixes PR4374.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73243 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 8 insertions, 15 deletions

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 03a7317138..5465e4a884 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2608,21 +2608,6 @@ Instruction *InstCombiner::visitFSub(BinaryOperator &I) {
       else if (Op1I->getOperand(1) == Op0)         // X-(Y+X) == -Y
         return BinaryOperator::CreateFNeg(Op1I->getOperand(0), I.getName());
     }
-
-    if (Op1I->hasOneUse()) {
-      // Replace (x - (y - z)) with (x + (z - y)) if the (y - z) subexpression
-      // is not used by anyone else...
-      //
-      if (Op1I->getOpcode() == Instruction::FSub) {
-        // Swap the two operands of the subexpr...
-        Value *IIOp0 = Op1I->getOperand(0), *IIOp1 = Op1I->getOperand(1);
-        Op1I->setOperand(0, IIOp1);
-        Op1I->setOperand(1, IIOp0);
-
-        // Create the new top level fadd instruction...
-        return BinaryOperator::CreateFAdd(Op0, Op1);
-      }
-    }
   }
 
   return 0;
diff --git a/test/Transforms/InstCombine/fsub-fsub.ll b/test/Transforms/InstCombine/fsub-fsub.ll
new file mode 100644
index 0000000000..ab70479204
--- /dev/null
+++ b/test/Transforms/InstCombine/fsub-fsub.ll
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep fsub | count 2
+; PR4374
+
+define float @func(float %a, float %b) nounwind {
+        %tmp3 = fsub float %a, %b
+        %tmp4 = fsub float -0.000000e+00, %tmp3
+        ret float %tmp4
+}