Teach DAG combine to fold x-x to 0.0 when unsafe FP math is enabled.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@156324 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c2b7f6c513a8c55599af14d35bf108539eb86d00..753ba937c06f8d6381b11defc87f030d473f9810 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5670,9 +5670,13 @@ SDValue DAGCombiner::visitFSUB(SDNode *N) {
                        GetNegatedExpression(N1, DAG, LegalOperations));
 
   // If 'unsafe math' is enabled, fold
+  //    (fsub x, x) -> 0.0 &
   //    (fsub x, (fadd x, y)) -> (fneg y) &
   //    (fsub x, (fadd y, x)) -> (fneg y)
   if (DAG.getTarget().Options.UnsafeFPMath) {
+    if (N0 == N1)
+      return DAG.getConstantFP(0.0f, VT);
+
     if (N1.getOpcode() == ISD::FADD) {
       SDValue N10 = N1->getOperand(0);
       SDValue N11 = N1->getOperand(1);

diff --git a/test/CodeGen/ARM/unsafe-fsub.ll b/test/CodeGen/ARM/unsafe-fsub.ll
new file mode 100644 (file)
index 0000000..3a4477d
--- /dev/null
+++ b/test/CodeGen/ARM/unsafe-fsub.ll
@@ -0,0 +1,18 @@
+; RUN: llc -march=arm -mcpu=cortex-a9 < %s | FileCheck -check-prefix=SAFE %s
+; RUN: llc -march=arm -mcpu=cortex-a9 -enable-unsafe-fp-math < %s | FileCheck -check-prefix=FAST %s
+
+target triple = "armv7-apple-ios"
+
+; SAFE: test
+; FAST: test
+define float @test(float %x, float %y) {
+entry:
+; SAFE: vmul.f32
+; SAFE: vsub.f32
+; FAST: mov r0, #0
+  %0 = fmul float %x, %y
+  %1 = fsub float %0, %0
+  ret float %1
+}
+
+