[DAGCombiner] Move or/xor/and opcode check in ReduceLoadOpStoreWidth before hasOneUse...

hasOneUse is not cheap on nodes with chain results that might have
many uses. By checking the opcode first, we can avoid a costly walk
of the use list on nodes we aren't interested in.

Found by investigating calls to hasNUsesOfValue from the example
provided in D123857.

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 491d29a..afa264f 100644 (file)
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -17375,11 +17375,15 @@ SDValue DAGCombiner::ReduceLoadOpStoreWidth(SDNode *N) {
   SDValue Ptr   = ST->getBasePtr();
   EVT VT = Value.getValueType();
 
-  if (ST->isTruncatingStore() || VT.isVector() || !Value.hasOneUse())
+  if (ST->isTruncatingStore() || VT.isVector())
     return SDValue();
 
   unsigned Opc = Value.getOpcode();
 
+  if ((Opc != ISD::OR && Opc != ISD::XOR && Opc != ISD::AND) ||
+      !Value.hasOneUse())
+    return SDValue();
+
   // If this is "store (or X, Y), P" and X is "(and (load P), cst)", where cst
   // is a byte mask indicating a consecutive number of bytes, check to see if
   // Y is known to provide just those bytes.  If so, we try to replace the
@@ -17404,8 +17408,7 @@ SDValue DAGCombiner::ReduceLoadOpStoreWidth(SDNode *N) {
   if (!EnableReduceLoadOpStoreWidth)
     return SDValue();
 
-  if ((Opc != ISD::OR && Opc != ISD::XOR && Opc != ISD::AND) ||
-      Value.getOperand(1).getOpcode() != ISD::Constant)
+  if (Value.getOperand(1).getOpcode() != ISD::Constant)
     return SDValue();
 
   SDValue N0 = Value.getOperand(0);