[llvm] [RISCV][ISel] Add codegen support for the experimental zabha extension (PR #80192)

[Alex Bradbury via llvm-commits]

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@@ -629,7 +629,10 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
 
   if (Subtarget.hasStdExtA()) {
     setMaxAtomicSizeInBitsSupported(Subtarget.getXLen());
-    setMinCmpXchgSizeInBits(32);
+    if (Subtarget.hasStdExtZabha())
+      setMinCmpXchgSizeInBits(8);
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asb wrote:

I think adding logic to widenPartwordATomicRMW is only caused if shouldExpandAtomicRMWInIR was not None would make sense.

https://github.com/llvm/llvm-project/pull/80192