[llvm] [DAGCombiner] Allow tryToFoldExtOfLoad to use a sextload for zext nneg. (PR #81714)

[Nikita Popov via llvm-commits]

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@@ -13154,20 +13154,41 @@ static SDValue tryToFoldExtOfExtload(SelectionDAG &DAG, DAGCombiner &Combiner,
 
 // fold ([s|z]ext (load x)) -> ([s|z]ext (truncate ([s|z]extload x)))
 // Only generate vector extloads when 1) they're legal, and 2) they are
-// deemed desirable by the target.
+// deemed desirable by the target. NonNegZExt can be set to true if a zero
+// extend has the nonneg flag to allow use of sextload if profitable.
 static SDValue tryToFoldExtOfLoad(SelectionDAG &DAG, DAGCombiner &Combiner,
                                   const TargetLowering &TLI, EVT VT,
                                   bool LegalOperations, SDNode *N, SDValue N0,
                                   ISD::LoadExtType ExtLoadType,
-                                  ISD::NodeType ExtOpc) {
+                                  ISD::NodeType ExtOpc,
+                                  bool NonNegZExt = false) {
+  if (!ISD::isNON_EXTLoad(N0.getNode()) || !ISD::isUNINDEXEDLoad(N0.getNode()))
+    return {};
+
+  // If this is zext nneg, see if it would make sense to treat it as a sext.
+  if (NonNegZExt) {
+    assert(ExtLoadType == ISD::ZEXTLOAD && ExtOpc == ISD::ZERO_EXTEND &&
+           "Unexpected load type or opcode");
+    for (SDNode::use_iterator UI = N0->use_begin(), UE = N0->use_end();
+         UI != UE; ++UI) {
+      SDNode *User = *UI;
----------------
nikic wrote:

```suggestion
    for (SDNode *User : N0->uses()) {
```
I think?

https://github.com/llvm/llvm-project/pull/81714