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

[Pierre van Houtryve via llvm-commits]

================
@@ -95,11 +98,78 @@ inline raw_ostream &operator<<(raw_ostream &OS, const ArgDescriptor &Arg) {
   return OS;
 }
 
-struct KernArgPreloadDescriptor : public ArgDescriptor {
-  KernArgPreloadDescriptor() {}
-  SmallVector<MCRegister> Regs;
+namespace KernArgPreload {
+
+enum HiddenArg {
+  HIDDEN_BLOCK_COUNT_X,
+  HIDDEN_BLOCK_COUNT_Y,
+  HIDDEN_BLOCK_COUNT_Z,
+  HIDDEN_GROUP_SIZE_X,
+  HIDDEN_GROUP_SIZE_Y,
+  HIDDEN_GROUP_SIZE_Z,
+  HIDDEN_REMAINDER_X,
+  HIDDEN_REMAINDER_Y,
+  HIDDEN_REMAINDER_Z,
+  END_HIDDEN_ARGS
 };
 
+// Stores information about a specific hidden argument.
+struct HiddenArgInfo {
+  // Offset in bytes from the location in the kernearg segment pointed to by
+  // the implicitarg pointer.
+  uint8_t Offset;
+  // The size of the hidden argument in bytes.
+  uint8_t Size;
+  // The name of the hidden argument in the kernel signature.
+  const char *Name;
+};
+
+struct HiddenArgUtils {
+  static constexpr HiddenArgInfo HiddenArgs[END_HIDDEN_ARGS] = {
+      {0, 4, "_hidden_block_count_x"}, {4, 4, "_hidden_block_count_y"},
+      {8, 4, "_hidden_block_count_z"}, {12, 2, "_hidden_group_size_x"},
+      {14, 2, "_hidden_group_size_y"}, {16, 2, "_hidden_group_size_z"},
+      {18, 2, "_hidden_remainder_x"},  {20, 2, "_hidden_remainder_y"},
+      {22, 2, "_hidden_remainder_z"}};
+
+  static HiddenArg getHiddenArgFromOffset(unsigned Offset) {
+    for (unsigned I = 0; I < END_HIDDEN_ARGS; ++I)
+      if (HiddenArgs[I].Offset == Offset)
+        return static_cast<HiddenArg>(I);
----------------
Pierre-vh wrote:

```suggestion
    for (unsigned I = 0; I < END_HIDDEN_ARGS; ++I) {
      if (HiddenArgs[I].Offset == Offset)
        return static_cast<HiddenArg>(I);
    }
```

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