Teach DAG combine to fold x-x to 0.0 when unsafe FP math is enabled.
llvm-svn: 156324
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index c2b7f6c..753ba93 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5670,9 +5670,13 @@
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/llvm/test/CodeGen/ARM/unsafe-fsub.ll b/llvm/test/CodeGen/ARM/unsafe-fsub.ll
new file mode 100644
index 0000000..3a4477d
--- /dev/null
+++ b/llvm/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
+}
+
+