[clang] [llvm] [Clang][AIX] Add -mloadtime-comment-vars flag to preserve identifying variables (PR #187986)

[Hubert Tong via llvm-commits]

================
@@ -0,0 +1,117 @@
+// Test -mloadtime-comment-vars= across a C++20 named-module boundary. Five
+// scenarios, each named by its FileCheck or -verify prefix:
+//
+//   MOD       — the module unit is built to a BMI with the option and then
+//               compiled to IR from the BMI (the two-phase flow build systems
+//               use). Exported, module-linkage, internal-linkage, and inline
+//               variables are all preserved: the implicit attribute is
+//               serialized, and the internal and inline variables reach
+//               CodeGen via the module-initializer list. The same IR is
+//               produced whether or not the option is repeated on the
+//               codegen step: the BMI already records the result.
+//   NOOPT +   — the same module unit built to a BMI without the option and
+//   NOOPTNOT    compiled to IR with it: nothing is preserved. The option
+//               applies to the compilation of the module unit itself, where
+//               semantic analysis runs.
+//   IMPORT +  — an importing TU naming the module-owned variable: the
+//   IMPORTNOT   variable is defined in the module unit, not here, so it is
+//               neither re-emitted nor preserved here, and the module-internal
+//               variable does not leak into the importer. The inline variable
+//               it references is re-emitted here as usual for inline
+//               variables, and that copy is preserved as well because the
+//               attribute travels with the declaration in the BMI.
+//   verify    — specializations instantiated here from the imported template
+//               definitions are diagnosed in this TU, at the pattern location
+//               in the module interface, with a note at the instantiation
+//               point.
+//
+//   Source      IR symbol        Expected treatment
+//   ------      ---------        ------------------
+//   ver         _ZW1M3ver        exported: preserved when the module unit is
+//                                compiled with the option
+//   build       _ZW1M5build      module linkage: preserved likewise
+//   priv        _ZL4priv         internal linkage: preserved likewise; never
+//                                emitted by an importing TU
+//   iv          _ZW1M2iv         exported inline: preserved by the module unit
+//                                (emitted there although unreferenced) and by
+//                                every importer that references it
+//   vt<int>     _ZW1M2vtIiE      instantiated in the importer: diagnosed there
+//   S<int>::m   _ZNW1M1SIiE1mE   instantiated in the importer: diagnosed there
+
+// RUN: split-file %s %t
+
+// RUN: %clang_cc1 -std=c++20 -triple powerpc64-ibm-aix \
+// RUN:   -mloadtime-comment-vars=_ZW1M3ver,_ZW1M5build,_ZL4priv,_ZW1M2iv \
+// RUN:   -emit-module-interface %t/m.cppm -o %t/m.pcm
+// RUN: %clang_cc1 -std=c++20 -triple powerpc64-ibm-aix \
+// RUN:   -mloadtime-comment-vars=_ZW1M3ver,_ZW1M5build,_ZL4priv,_ZW1M2iv \
+// RUN:   -emit-llvm %t/m.pcm -o - | FileCheck %s --check-prefix=MOD
+// RUN: %clang_cc1 -std=c++20 -triple powerpc64-ibm-aix \
+// RUN:   -emit-llvm %t/m.pcm -o - | FileCheck %s --check-prefix=MOD
+
+// RUN: %clang_cc1 -std=c++20 -triple powerpc64-ibm-aix \
+// RUN:   -emit-module-interface %t/m.cppm -o %t/m-noopt.pcm
+// RUN: %clang_cc1 -std=c++20 -triple powerpc64-ibm-aix \
+// RUN:   -mloadtime-comment-vars=_ZW1M3ver,_ZW1M5build,_ZL4priv,_ZW1M2iv \
+// RUN:   -emit-llvm %t/m-noopt.pcm -o %t/m-noopt.ll
+// RUN: FileCheck %s --check-prefix=NOOPT < %t/m-noopt.ll
+// RUN: FileCheck %s --check-prefix=NOOPTNOT < %t/m-noopt.ll
+
+// RUN: %clang_cc1 -std=c++20 -triple powerpc64-ibm-aix \
+// RUN:   -fmodule-file=M=%t/m.pcm -mloadtime-comment-vars=_ZW1M3ver \
+// RUN:   -emit-llvm %t/use.cpp -o %t/use.ll
+// RUN: FileCheck %s --check-prefix=IMPORT < %t/use.ll
+// RUN: FileCheck %s --check-prefix=IMPORTNOT < %t/use.ll
+
+// RUN: %clang_cc1 -std=c++20 -triple powerpc64-ibm-aix \
+// RUN:   -fmodule-file=M=%t/m.pcm \
+// RUN:   -mloadtime-comment-vars=_ZW1M2vtIiE,_ZNW1M1SIiE1mE \
+// RUN:   -fsyntax-only -verify %t/use.cpp
+
+// All four variables carry the metadata and are kept in llvm.compiler.used
+// when the module unit is compiled from a BMI that was built with the option.
+// MOD-DAG: @_ZW1M3ver = global [16 x i8] c"@(#) module ver\00", align 1, !loadtime_comment ![[MD:[0-9]+]]
+// MOD-DAG: @_ZW1M5build = global [18 x i8] c"@(#) module build\00", align 1, !loadtime_comment ![[MD]]
+// MOD-DAG: @_ZL4priv = internal global [17 x i8] c"@(#) module priv\00", align 1, !loadtime_comment ![[MD]]
+// MOD-DAG: @_ZW1M2iv = linkonce_odr global ptr @{{.*}}, align 8, !loadtime_comment ![[MD]]
+// MOD-DAG: @llvm.compiler.used = appending global [4 x ptr]
+
+// Without the option at BMI-build time nothing is preserved: the exported
+// variable is an ordinary global (the {{$}} anchor proves no metadata), and
+// the unreferenced internal and inline variables are not emitted at all.
+// NOOPT: @_ZW1M3ver = global [16 x i8] c"@(#) module ver\00", align 1{{$}}
----------------
hubert-reinterpretcast wrote:

The non-exported module linkage variable is defined but not preserved as well?

https://github.com/llvm/llvm-project/pull/187986