[clang] [Clang][Driver] Expose `-fno-eliminate-unused-debug-types` to clang-cl (PR #95259)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-driver

Author: Alexandre Ganea (aganea)

<details>
<summary>Changes</summary>

This is used to set DebugInfoKind to "UnusedTypeInfo". This helps in the context Unreal Engine and NATVIS files that reference unused otherwise `static constexpr` class members. See https://udn.unrealengine.com/s/question/0D5QP00000N012h0AB/fname-debug-visualizer-fails-to-work-with-the-clang-compiler

This fixes https://github.com/llvm/llvm-project/issues/46924

---
Full diff: https://github.com/llvm/llvm-project/pull/95259.diff


3 Files Affected:

- (modified) clang/docs/UsersManual.rst (+3) 
- (modified) clang/include/clang/Driver/Options.td (+1-1) 
- (modified) clang/test/Driver/cl-options.c (+2) 


``````````diff
diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index f954857b0235a..d36db8a01949c 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -3338,6 +3338,9 @@ below. If multiple flags are present, the last one is used.
   By default, Clang does not emit type information for types that are defined
   but not used in a program. To retain the debug info for these unused types,
   the negation **-fno-eliminate-unused-debug-types** can be used.
+  This can be particulary useful on Windows, when using NATVIS files that
+  can reference const symbols that would otherwise be stripped, even in full
+  debug or standalone debug modes.
 
 Controlling Macro Debug Info Generation
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 9f7904dd94b94..b75d67551bc97 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -2120,7 +2120,7 @@ def fno_elide_type : Flag<["-"], "fno-elide-type">, Group<f_Group>,
     MarshallingInfoNegativeFlag<DiagnosticOpts<"ElideType">>;
 def feliminate_unused_debug_symbols : Flag<["-"], "feliminate-unused-debug-symbols">, Group<f_Group>;
 defm eliminate_unused_debug_types : OptOutCC1FFlag<"eliminate-unused-debug-types",
-  "Do not emit ", "Emit ", " debug info for defined but unused types">;
+  "Do not emit ", "Emit ", " debug info for defined but unused types", [ClangOption, CLOption]>;
 def femit_all_decls : Flag<["-"], "femit-all-decls">, Group<f_Group>,
   Visibility<[ClangOption, CC1Option]>,
   HelpText<"Emit all declarations, even if unused">,
diff --git a/clang/test/Driver/cl-options.c b/clang/test/Driver/cl-options.c
index 2c17459dde656..d7d7c5c825815 100644
--- a/clang/test/Driver/cl-options.c
+++ b/clang/test/Driver/cl-options.c
@@ -696,6 +696,8 @@
 // RUN:     -Wunused-variable \
 // RUN:     -fmacro-backtrace-limit=0 \
 // RUN:     -fstandalone-debug \
+// RUN:     -feliminate-unused-debug-types \
+// RUN:     -fno-eliminate-unused-debug-types \
 // RUN:     -flimit-debug-info \
 // RUN:     -flto \
 // RUN:     -fmerge-all-constants \

``````````

</details>


https://github.com/llvm/llvm-project/pull/95259