[llvm] [Xtensa] Implement Xtensa S32C1I Option and atomics lowering. (PR #137134)

[Matt Arsenault via llvm-commits]

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@@ -175,6 +175,40 @@ XtensaTargetLowering::XtensaTargetLowering(const TargetMachine &TM,
   setOperationAction(ISD::VACOPY, MVT::Other, Custom);
   setOperationAction(ISD::VAEND, MVT::Other, Expand);
 
+    // to have the best chance and doing something good with fences custom lower
+  // them
+  setOperationAction(ISD::ATOMIC_FENCE, MVT::Other, Custom);
+
+  if (!Subtarget.hasS32C1I()) {
+    for (unsigned I = MVT::FIRST_INTEGER_VALUETYPE;
+         I <= MVT::LAST_INTEGER_VALUETYPE; ++I) {
+      MVT VT = MVT::SimpleValueType(I);
+      if (isTypeLegal(VT)) {
+        setOperationAction(ISD::ATOMIC_CMP_SWAP, VT, Expand);
+        setOperationAction(ISD::ATOMIC_SWAP, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_ADD, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_SUB, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_AND, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_OR, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_XOR, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_NAND, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_MIN, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_MAX, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_UMIN, VT, Expand);
+        setOperationAction(ISD::ATOMIC_LOAD_UMAX, VT, Expand);
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arsenm wrote:

I'm not sure any of this is doing anything. The default expansion only emits the libcall (really should migrate these to using the explicit libcall action..), and I'm not sure what the default is for the atomic runtime libcalls.

To expand atomics you need to override shouldExpandAtomicRMWInIR

https://github.com/llvm/llvm-project/pull/137134