Implement cond ? -1 : 0 with sbb.

llvm-svn: 94490

1 files changed, 25 insertions, 2 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index aae17a8cf1b..e53f6b7525b 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -5965,6 +5965,29 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) {
       Cond = NewCond;
   }
 
+  // (select (x == 0), -1, 0) -> (sign_bit (x - 1))
+  SDValue Op1 = Op.getOperand(1);
+  SDValue Op2 = Op.getOperand(2);
+  if (Cond.getOpcode() == X86ISD::SETCC &&
+      cast<ConstantSDNode>(Cond.getOperand(0))->getZExtValue() == X86::COND_E) {
+    SDValue Cmp = Cond.getOperand(1);
+    if (Cmp.getOpcode() == X86ISD::CMP) {
+      ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(Op1);
+      ConstantSDNode *N2C = dyn_cast<ConstantSDNode>(Op2);
+      ConstantSDNode *RHSC =
+        dyn_cast<ConstantSDNode>(Cmp.getOperand(1).getNode());
+      if (N1C && N1C->isAllOnesValue() &&
+          N2C && N2C->isNullValue() &&
+          RHSC && RHSC->isNullValue()) {
+        SDValue CmpOp0 = Cmp.getOperand(0);
+        Cmp = DAG.getNode(X86ISD::CMP, dl, Op.getValueType(),
+                          CmpOp0, DAG.getConstant(1, CmpOp0.getValueType()));
+        return DAG.getNode(X86ISD::SETCC_CARRY, dl, Op.getValueType(),
+                           DAG.getConstant(X86::COND_B, MVT::i8), Cmp);
+      }
+    }
+  }
+
   // Look pass (and (setcc_carry (cmp ...)), 1).
   if (Cond.getOpcode() == ISD::AND &&
       Cond.getOperand(0).getOpcode() == X86ISD::SETCC_CARRY) {
@@ -6017,10 +6040,10 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) {
     Cond = EmitTest(Cond, X86::COND_NE, DAG);
   }
 
-  SDVTList VTs = DAG.getVTList(Op.getValueType(), MVT::Flag);
   // X86ISD::CMOV means set the result (which is operand 1) to the RHS if
   // condition is true.
-  SDValue Ops[] = { Op.getOperand(2), Op.getOperand(1), CC, Cond };
+  SDVTList VTs = DAG.getVTList(Op.getValueType(), MVT::Flag);
+  SDValue Ops[] = { Op2, Op1, CC, Cond };
   return DAG.getNode(X86ISD::CMOV, dl, VTs, Ops, array_lengthof(Ops));
 }