[x86] use BMI 'andn' for logic + compare ops

With BMI, we can use 'andn' to save an instruction when the result is only used in a compare.
This is related to one of the potential sequences to check 'isfinite' in:
https://llvm.org/bugs/show_bug.cgi?id=27164

Differential Revision: http://reviews.llvm.org/D18910

llvm-svn: 265875

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 1183c5cbc83..a28ce41a660 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6708,6 +6708,10 @@ bool llvm::isOneConstant(SDValue V) {
   return Const != nullptr && Const->isOne();
 }
 
+bool llvm::isBitwiseNot(SDValue V) {
+  return V.getOpcode() == ISD::XOR && isAllOnesConstant(V.getOperand(1));
+}
+
 HandleSDNode::~HandleSDNode() {
   DropOperands();
 }