[llvm] [AMDGPU][True16][CodeGen] update waitcnt for true16 (PR #128927)

[Matt Arsenault via llvm-commits]

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@@ -64,6 +64,8 @@ class SIRegisterInfo final : public AMDGPUGenRegisterInfo {
     bool hasReg() { return VGPR != 0; }
   };
 
+  const GCNSubtarget &getSubtarget() const { return ST; }
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arsenm wrote:

Shouldn't need this, the pass already has the subtarget 

https://github.com/llvm/llvm-project/pull/128927