[llvm] [AMDGPU] Set glc/slc on volatile/nontemporal SMEM loads (PR #77443)

[Jay Foad via llvm-commits]

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@@ -29,7 +29,6 @@ class SM_Pseudo <string opName, dag outs, dag ins, string asmOps, list<dag> patt
   let mayStore = 0;
   let mayLoad = 1;
   let hasSideEffects = 0;
-  let maybeAtomic = 0;
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jayfoad wrote:

> How does removing this cause SIMemoryLegalizer to process scalar loads and stores?

Not setting `maybeAtomic = 0` on SMEM Pseudos means that they all inherit the default of `maybeAtomic = 1`. The main loop in `SIMemoryLegalizer::runOnMachineFunction` ignores anything that is not marked as `maybeAtomic`.

> Should the memory model in AMDGPUUsage be updated to include the scalar memory instructions?

Probably. Are you saying that should be a prerequisite for this patch?

https://github.com/llvm/llvm-project/pull/77443