[mips] Account for constant-zero operands in ADDE nodes.
Summary:
We identify the cases where the operand to an ADDE node is a constant
zero. In such cases, we can avoid generating an extra ADDu instruction
disguised as an identity move alias (ie. addu $r, $r, 0 --> move $r, $r).
Reviewers: dsanders
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D7906
llvm-svn: 230742
diff --git a/llvm/lib/Target/Mips/MipsSEISelDAGToDAG.cpp b/llvm/lib/Target/Mips/MipsSEISelDAGToDAG.cpp
index 0761ded..4da30be 100644
--- a/llvm/lib/Target/Mips/MipsSEISelDAGToDAG.cpp
+++ b/llvm/lib/Target/Mips/MipsSEISelDAGToDAG.cpp
@@ -258,8 +258,12 @@
CurDAG->getTargetConstant(Mips::sub_32, VT));
}
- SDNode *AddCarry = CurDAG->getMachineNode(ADDuOp, DL, VT,
- SDValue(Carry, 0), RHS);
+ // Generate a second addition only if we know that RHS is not a
+ // constant-zero node.
+ SDNode *AddCarry = Carry;
+ ConstantSDNode *C = dyn_cast<ConstantSDNode>(RHS);
+ if (!C || C->getZExtValue())
+ AddCarry = CurDAG->getMachineNode(ADDuOp, DL, VT, SDValue(Carry, 0), RHS);
return CurDAG->SelectNodeTo(Node, MOp, VT, MVT::Glue, LHS,
SDValue(AddCarry, 0));