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

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 83c357d70803dd3f85556d5fd7a3826439ab63ef..660a1bd0bdf6597d65790283d3094f6df662e49c 100644 (file)
--- 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);

diff --git a/test/CodeGen/X86/select.ll b/test/CodeGen/X86/select.ll
index 9adf4f9c050dd566fb193934479155ec709e85e0..5730f618e4ec2f5eebb602e0b48411dad7da3a81 100644 (file)
--- a/test/CodeGen/X86/select.ll
+++ b/test/CodeGen/X86/select.ll
@@ -218,3 +218,24 @@ define i32 @test14(i32 %a, i32 %b) nounwind {
 ; CHECK-NEXT: ret
 }
 
+; rdar://10961709
+define i32 @test15(i32 %x) nounwind {
+entry:
+  %cmp = icmp ne i32 %x, 0
+  %sub = sext i1 %cmp to i32
+  ret i32 %sub
+; CHECK: test15:
+; CHECK: negl
+; CHECK: sbbl
+}
+
+define i32 @test16(i32 %x) nounwind {
+entry:
+  %c = icmp eq i32 %x, 0
+  %d = select i1 %c, i32 0, i32 -1
+  ret i32 %d
+; CHECK: test16:
+; CHECK: negl
+; CHECK: sbbl
+}
+