[llvm] [AMDGPU] Filter candidates of LiveRegOptimizer for profitable cases (PR #124624)

[via llvm-commits]

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@@ -45,6 +46,7 @@ class AMDGPULateCodeGenPrepare
   Function &F;
   const DataLayout &DL;
   const GCNSubtarget &ST;
+  const TargetTransformInfo &TTI;
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choikwa wrote:

TTI acts as interface class I believe. Below is what gets returned.
```
TargetTransformInfo
GCNTargetMachine::getTargetTransformInfo(const Function &F) const {
  return TargetTransformInfo(GCNTTIImpl(this, F));
}
```

https://github.com/llvm/llvm-project/pull/124624