[llvm] [AMDGPU] Update code object metadata for kernarg preload (PR #134666)

[Matt Arsenault via llvm-commits]

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@@ -160,15 +234,34 @@ struct AMDGPUFunctionArgInfo {
   ArgDescriptor WorkItemIDY;
   ArgDescriptor WorkItemIDZ;
 
+  struct PreloadArgIndexFunctor {
+    using argument_type = unsigned;
+    unsigned operator()(unsigned Idx) const { return Idx; }
+  };
+
   // Map the index of preloaded kernel arguments to its descriptor.
-  SmallDenseMap<int, KernArgPreloadDescriptor> PreloadKernArgs{};
+  IndexedMap<KernArgPreload::KernArgPreloadDescriptor, PreloadArgIndexFunctor>
+      PreloadKernArgs;
+
+  // Map hidden argument to the index of it's descriptor.
+  SmallDenseMap<KernArgPreload::HiddenArg, int> PreloadHiddenArgsIndexMap{};
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arsenm wrote:

```suggestion
  SmallDenseMap<KernArgPreload::HiddenArg, int> PreloadHiddenArgsIndexMap;
```

https://github.com/llvm/llvm-project/pull/134666