X86: optimization for -(x != 0)

This patch will optimize -(x != 0) on X86
FROM 
cmpl	$0x01,%edi
sbbl	%eax,%eax
notl	%eax
TO
negl %edi
sbbl %eax %eax


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155853 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 83c357d708..660a1bd0bd 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -8589,6 +8589,22 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) const {
       SDValue Y = isAllOnes(Op2) ? Op1 : Op2;
 
       SDValue CmpOp0 = Cmp.getOperand(0);
+      // further optimization for special cases
+      // (select (x != 0), -1, 0) -> neg & sbb
+      // (select (x == 0), 0, -1) -> neg & sbb
+      if (ConstantSDNode *YC = dyn_cast<ConstantSDNode>(Y))
+        if (YC->isNullValue() && 
+            (isAllOnes(Op1) == (CondCode == X86::COND_NE))) {
+          SDVTList VTs = DAG.getVTList(CmpOp0.getValueType(), MVT::i32);
+          SDValue Neg = DAG.getNode(ISD::SUB, DL, VTs, 
+                                    DAG.getConstant(0, CmpOp0.getValueType()), 
+                                    CmpOp0);
+          SDValue Res = DAG.getNode(X86ISD::SETCC_CARRY, DL, Op.getValueType(),
+                                    DAG.getConstant(X86::COND_B, MVT::i8),
+                                    SDValue(Neg.getNode(), 1));
+          return Res;
+        }
+
       Cmp = DAG.getNode(X86ISD::CMP, DL, MVT::i32,
                         CmpOp0, DAG.getConstant(1, CmpOp0.getValueType()));
       Cmp = ConvertCmpIfNecessary(Cmp, DAG);