Shrink shifts when possible.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28136 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 872242e..1175f52 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1615,6 +1615,18 @@
DAG.getConstant(c1 + c2, N1.getValueType()));
}
+ // fold (srl (anyextend x), c) -> (anyextend (srl x, c))
+ if (N1C && N0.getOpcode() == ISD::ANY_EXTEND) {
+ // Shifting in all undef bits?
+ MVT::ValueType SmallVT = N0.getOperand(0).getValueType();
+ if (N1C->getValue() >= MVT::getSizeInBits(SmallVT))
+ return DAG.getNode(ISD::UNDEF, VT);
+
+ SDOperand SmallShift = DAG.getNode(ISD::SRL, SmallVT, N0.getOperand(0), N1);
+ AddToWorkList(SmallShift.Val);
+ return DAG.getNode(ISD::ANY_EXTEND, VT, SmallShift);
+ }
+
// fold (srl (ctlz x), "5") -> x iff x has one bit set (the low bit).
if (N1C && N0.getOpcode() == ISD::CTLZ &&
N1C->getValue() == Log2_32(MVT::getSizeInBits(VT))) {