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

The folding of sign/zero extensions into an atomic load by specifying an
extension type is not target specific, and therefore belongs in the
DAGCombiner rather than in the SystemZ backend.

- Handle atomic loads similarly to regular loads by adding
AtomicLoadExtActions with set/get methods.
- Move SystemZ extendAtomicLoad() to DagCombiner.cpp.

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index b16e78d..f64ded4 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -823,6 +823,12 @@ void TargetLoweringBase::initActions() {
   std::fill(std::begin(TargetDAGCombineArray),
             std::end(TargetDAGCombineArray), 0);
 
+  // Let extending atomic loads be unsupported by default.
+  for (MVT ValVT : MVT::all_valuetypes())
+    for (MVT MemVT : MVT::all_valuetypes())
+      setAtomicLoadExtAction({ISD::SEXTLOAD, ISD::ZEXTLOAD}, ValVT, MemVT,
+                             Expand);
+
   // We're somewhat special casing MVT::i2 and MVT::i4. Ideally we want to
   // remove this and targets should individually set these types if not legal.
   for (ISD::NodeType NT : enum_seq(ISD::DELETED_NODE, ISD::BUILTIN_OP_END,