[llvm] r217286 - Allow vector fsub ops with constants to get the same optimizations as scalars.

[Sanjay Patel]

Author: spatel
Date: Fri Sep  5 17:26:22 2014
New Revision: 217286

URL: http://llvm.org/viewvc/llvm-project?rev=217286&view=rev
Log:
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.


Added:
    llvm/trunk/test/CodeGen/X86/vec_unsafe-fp-math.ll
Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp?rev=217286&r1=217285&r2=217286&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/DAGCombiner.cpp Fri Sep  5 17:26:22 2014
@@ -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;

Added: llvm/trunk/test/CodeGen/X86/vec_unsafe-fp-math.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/vec_unsafe-fp-math.ll?rev=217286&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/X86/vec_unsafe-fp-math.ll (added)
+++ llvm/trunk/test/CodeGen/X86/vec_unsafe-fp-math.ll Fri Sep  5 17:26:22 2014
@@ -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
+}