Now that ShrinkDemandedOps() is separated out from DAG combine. It sometimes leave some obvious nops which dag combine used to clean up afterwards e.g. (trunk (ext n)) -> n. Look for them and squash them.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95757 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 679b338..da2e6e4 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -457,6 +457,21 @@
};
}
+/// TrivialTruncElim - Eliminate some trivial nops that can result from
+/// ShrinkDemandedOps: (trunc (ext n)) -> n.
+static bool TrivialTruncElim(SDValue Op,
+ TargetLowering::TargetLoweringOpt &TLO) {
+ SDValue N0 = Op.getOperand(0);
+ EVT VT = Op.getValueType();
+ if ((N0.getOpcode() == ISD::ZERO_EXTEND ||
+ N0.getOpcode() == ISD::SIGN_EXTEND ||
+ N0.getOpcode() == ISD::ANY_EXTEND) &&
+ N0.getOperand(0).getValueType() == VT) {
+ return TLO.CombineTo(Op, N0.getOperand(0));
+ }
+ return false;
+}
+
/// ShrinkDemandedOps - A late transformation pass that shrink expressions
/// using TargetLowering::TargetLoweringOpt::ShrinkDemandedOp. It converts
/// x+y to (VT)((SmallVT)x+(SmallVT)y) if the casts are free.
@@ -489,7 +504,9 @@
APInt Demanded = APInt::getAllOnesValue(BitWidth);
APInt KnownZero, KnownOne;
if (TLI.SimplifyDemandedBits(SDValue(N, 0), Demanded,
- KnownZero, KnownOne, TLO)) {
+ KnownZero, KnownOne, TLO) ||
+ (N->getOpcode() == ISD::TRUNCATE &&
+ TrivialTruncElim(SDValue(N, 0), TLO))) {
// Revisit the node.
Worklist.erase(std::remove(Worklist.begin(), Worklist.end(), N),
Worklist.end());