[llvm] [NVPTX] add support for 128-bit atomics (PR #154852)

[Alex MacLean via llvm-commits]

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@@ -1026,15 +1026,19 @@ NVPTXTargetLowering::NVPTXTargetLowering(const NVPTXTargetMachine &TM,
   setOperationAction(ISD::ADDRSPACECAST, {MVT::i32, MVT::i64}, Custom);
 
   setOperationAction(ISD::ATOMIC_LOAD_SUB, {MVT::i32, MVT::i64}, Expand);
-  // No FPOW or FREM in PTX.
+
+  // atom.b128 is legal in PTX but since we don't represent i128 as a legal
+  // type, we need to custom lower it.
+  setOperationAction({ISD::ATOMIC_CMP_SWAP, ISD::ATOMIC_SWAP}, MVT::i128,
+                     Custom);
 
   // Now deduce the information based on the above mentioned
   // actions
   computeRegisterProperties(STI.getRegisterInfo());
 
   // PTX support for 16-bit CAS is emulated. Only use 32+
   setMinCmpXchgSizeInBits(STI.getMinCmpXchgSizeInBits());
-  setMaxAtomicSizeInBitsSupported(64);
+  setMaxAtomicSizeInBitsSupported(128);
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AlexMaclean wrote:

I've updated this as suggested since it seems like there is consensus amongst the reviewers that we want to make this conditional on the sub-target.

https://github.com/llvm/llvm-project/pull/154852