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

[Hubert Tong via cfe-commits]

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@@ -0,0 +1,150 @@
+//===-- LowerCommentStringPass.cpp - Lower Comment string metadata -------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+//
+// This pass lowers the module-level comment string metadata emitted by Clang:
+//
+//     !comment_string.loadtime = !{!"Copyright ..."}
+//
+// into concrete, translation-unit-local globals.
+// This Pass is enabled only for AIX.
+// For each module (translation unit), the pass performs the following:
+//
+//   1. Creates a null-terminated, internal constant string global
+//      (`__loadtime_comment_str`) containing the copyright text with
+//      section attribute "__loadtime_comment". The backend places this
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hubert-reinterpretcast wrote:

There needs to be more rationale here for using a named section. What is the benefit of having it?

My understanding is that it interacts with (full) LTO such that the linker is less able to garbage-collect individual strings. Perhaps that is fine as the general intent seems to be for the strings to be kept.

A possible benefit of the named section is that the strings are more likely to be grouped in a block that does not interfere with the rest of the program.

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