add a simple dag combine to replace trivial shl+lshr with
and. This happens with the store->load narrowing stuff.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101348 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 671c507..5974aff 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2735,6 +2735,15 @@
return DAG.getNode(ISD::SRL, N->getDebugLoc(), VT, N0.getOperand(0),
DAG.getConstant(c1 + c2, N1.getValueType()));
}
+
+ // fold (srl (shl x, c), c) -> (and x, cst2)
+ if (N1C && N0.getOpcode() == ISD::SHL && N0.getOperand(1) == N1 &&
+ N0.getValueSizeInBits() <= 64) {
+ uint64_t ShAmt = N1C->getZExtValue()+64-N0.getValueSizeInBits();
+ return DAG.getNode(ISD::AND, N->getDebugLoc(), VT, N0.getOperand(0),
+ DAG.getConstant(~0ULL >> ShAmt, VT));
+ }
+
// fold (srl (anyextend x), c) -> (anyextend (srl x, c))
if (N1C && N0.getOpcode() == ISD::ANY_EXTEND) {