[llvm] [AMDGPU] Implement readcyclecounter for GFX12 (PR #76965)

[Matt Arsenault via llvm-commits]

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@@ -4827,6 +4827,48 @@ MachineBasicBlock *SITargetLowering::EmitInstrWithCustomInserter(
     MI.eraseFromParent();
     return BB;
   }
+  case AMDGPU::GET_SHADERCYCLESHILO: {
+    assert(MF->getSubtarget<GCNSubtarget>().hasShaderCyclesHiLoRegisters());
+    MachineRegisterInfo &MRI = MF->getRegInfo();
+    DebugLoc DL = MI.getDebugLoc();
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arsenm wrote:

const ref 

https://github.com/llvm/llvm-project/pull/76965