[llvm] [AMDGPU][Attributor] Rework update of `AAAMDWavesPerEU` (PR #123995)

[Johannes Doerfert via llvm-commits]

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@@ -1323,6 +1298,73 @@ struct AAAMDGPUNoAGPR
 
 const char AAAMDGPUNoAGPR::ID = 0;
 
+/// Performs the final check and updates the 'amdgpu-waves-per-eu' attribute
+/// based on the finalized 'amdgpu-flat-work-group-size' attribute.
+/// Both attributes start with narrow ranges that expand during iteration.
+/// However, a narrower flat-workgroup-size leads to a wider waves-per-eu range,
+/// preventing optimal updates later. Therefore, waves-per-eu can't be updated
+/// with intermediate values during the attributor run. We defer the calculation
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jdoerfert wrote:

```suggestion
/// with intermediate values during the attributor run. We defer the finalization
```

https://github.com/llvm/llvm-project/pull/123995