Allow vector fsub ops with constants to get the same optimizations as scalars.

This problem is bigger than just fsub, but this is the minimum fix to solve
fneg for PR20556 ( http://llvm.org/bugs/show_bug.cgi?id=20556 ), and we solve
zero subtraction with the same change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217286 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 5d95af6..a465cdb 100644 (file)
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6754,8 +6754,8 @@ SDValue DAGCombiner::visitFADD(SDNode *N) {
 SDValue DAGCombiner::visitFSUB(SDNode *N) {
   SDValue N0 = N->getOperand(0);
   SDValue N1 = N->getOperand(1);
-  ConstantFPSDNode *N0CFP = dyn_cast<ConstantFPSDNode>(N0);
-  ConstantFPSDNode *N1CFP = dyn_cast<ConstantFPSDNode>(N1);
+  ConstantFPSDNode *N0CFP = isConstOrConstSplatFP(N0);
+  ConstantFPSDNode *N1CFP = isConstOrConstSplatFP(N1);
   EVT VT = N->getValueType(0);
   SDLoc dl(N);
   const TargetOptions &Options = DAG.getTarget().Options;

diff --git a/test/CodeGen/X86/vec_unsafe-fp-math.ll b/test/CodeGen/X86/vec_unsafe-fp-math.ll
new file mode 100644 (file)
index 0000000..827d418
--- /dev/null
+++ b/test/CodeGen/X86/vec_unsafe-fp-math.ll
@@ -0,0 +1,23 @@
+; RUN: llc < %s -enable-unsafe-fp-math -mtriple=x86_64-unknown-unknown -mcpu=corei7 | FileCheck %s
+
+; Make sure that vectors get the same benefits as scalars when using unsafe-fp-math.
+
+; Subtracting zero is free.
+define <4 x float> @vec_fsub_zero(<4 x float> %x) {
+; CHECK-LABEL: vec_fsub_zero:
+; CHECK-NOT: subps
+; CHECK-NOT: xorps
+; CHECK: retq
+  %sub = fsub <4 x float> %x, zeroinitializer
+  ret <4 x float> %sub
+}
+
+; Negating doesn't require subtraction.
+define <4 x float> @vec_fneg(<4 x float> %x) {
+; CHECK-LABEL: vec_fneg:
+; CHECK: xorps  {{.*}}LCP{{.*}}, %xmm0
+; CHECK-NOT: subps
+; CHECK-NEXT: retq
+  %sub = fsub <4 x float> zeroinitializer, %x
+  ret <4 x float> %sub
+}