[llvm] [DAGCombiner] Move handling of atomic loads from SystemZ to DAGCombiner (NFC). (PR #86484)

[Jonas Paulsson via llvm-commits]

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@@ -13131,6 +13131,37 @@ tryToFoldExtOfMaskedLoad(SelectionDAG &DAG, const TargetLowering &TLI, EVT VT,
   return NewLoad;
 }
 
+// fold ([s|z]ext (atomic_load)) -> ([s|z]ext (truncate ([s|z]ext atomic_load)))
+static SDValue tryToFoldExtOfAtomicLoad(SelectionDAG &DAG,
+                                        const TargetLowering &TLI, EVT VT,
+                                        SDValue N0,
+                                        ISD::LoadExtType ExtLoadType) {
+  auto *ALoad = dyn_cast<AtomicSDNode>(N0);
+  if (!ALoad || ALoad->getOpcode() != ISD::ATOMIC_LOAD)
+    return {};
+  EVT MemoryVT = ALoad->getMemoryVT();
+  if (!TLI.isAtomicLoadExtLegal(ExtLoadType, VT, MemoryVT))
+    return {};
+  // Can't fold into atomic_load if it is already extending differently.
+  ISD::LoadExtType ALoadExtTy = ALoad->getExtensionType();
+  if ((ALoadExtTy == ISD::ZEXTLOAD && ExtLoadType == ISD::SEXTLOAD) ||
+      (ALoadExtTy == ISD::SEXTLOAD && ExtLoadType == ISD::ZEXTLOAD))
+    return {};
+
+  EVT OrigVT = ALoad->getValueType(0);
+  assert(OrigVT.getSizeInBits() < VT.getSizeInBits() && "VT should be wider.");
+  auto *NewALoad = dyn_cast<AtomicSDNode>(DAG.getAtomic(
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JonPsson1 wrote:

fixed.

https://github.com/llvm/llvm-project/pull/86484