[clang] [llvm] [PowerPC][AIX] Support #pragma comment copyright for AIX (PR #178184)

[Tony Varghese via cfe-commits]

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@@ -1472,6 +1473,9 @@ PassBuilder::buildModuleOptimizationPipeline(OptimizationLevel Level,
   const bool LTOPreLink = isLTOPreLink(LTOPhase);
   ModulePassManager MPM;
 
+  // Process copyright metadata early, before any optimizations
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tonykuttai wrote:

The design rationale was to get an IR pass to replace the metadata with an IR definition and create the necessary `.ref`s in the IR from the definitions in the IR. Thus, the metadata only survives from the point of the front-end codegen until that IR pass. Basically we want the follwoing:

- Clang frontend emits `!comment_string.loadtime` metadata (survives only until the IR pass)
- `LowerCommentStringPass` runs early in the per-TU pipeline, converts the metadata into a concrete `@__loadtime_comment_str` global and attaches `!implicit.ref` to all defined functions
- backend reads `!implicit.ref` and emits `.ref` directives into the object file
- By the time LTO runs, the metadata is already consumed and concrete globals + `.ref` directives are already in the object file.

https://github.com/llvm/llvm-project/pull/178184