[clang] [CLANG][DWARF] Do not emit -ggnu-pubnames for split dwarf version 5. (PR #82840)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Alexander Yermolovich (ayermolo)

<details>
<summary>Changes</summary>

When -gsplit-dwarf is passed in clang emmmits -ggnu-pubnames which results in
.debug_gnu_pubnames/..debug_gnu_pubtypes being generated. For DWARF5 we have
functional .debug_names.

TBH not sure what the right behavior should be. Should we not generate anything
at all by default or generate .debug_names? Doing some archeological digging
initially -gnu-pubnames was always generated to be in line with what gcc does.. It was then
changed so that it was generated when split-dwarf was enabled:
https://github.com/llvm/llvm-project/commit/658645241bf0c624d4b7a67c195c239bbc193e3f#diff-bac41c71569f27df21a843bcd74d2e604ed508afbdf141777761dfb545c5d228

For LLDB these gnu sections are not useful and just waste space. Maybe a better
check is to be based on tunning?


---
Full diff: https://github.com/llvm/llvm-project/pull/82840.diff


2 Files Affected:

- (modified) clang/lib/Driver/ToolChains/Clang.cpp (+4-3) 
- (modified) clang/test/Driver/split-debug.c (-1) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 6e1b7e8657d0dc..27a5aef17c8d71 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -4479,9 +4479,10 @@ renderDebugOptions(const ToolChain &TC, const Driver &D, const llvm::Triple &T,
                       options::OPT_gpubnames, options::OPT_gno_pubnames);
   if (DwarfFission != DwarfFissionKind::None ||
       (PubnamesArg && checkDebugInfoOption(PubnamesArg, Args, D, TC)))
-    if (!PubnamesArg ||
-        (!PubnamesArg->getOption().matches(options::OPT_gno_gnu_pubnames) &&
-         !PubnamesArg->getOption().matches(options::OPT_gno_pubnames)))
+    if (EffectiveDWARFVersion < 5 &&
+        (!PubnamesArg ||
+         (!PubnamesArg->getOption().matches(options::OPT_gno_gnu_pubnames) &&
+          !PubnamesArg->getOption().matches(options::OPT_gno_pubnames))))
       CmdArgs.push_back(PubnamesArg && PubnamesArg->getOption().matches(
                                            options::OPT_gpubnames)
                             ? "-gpubnames"
diff --git a/clang/test/Driver/split-debug.c b/clang/test/Driver/split-debug.c
index 968f33b4cc035c..1d5f0fa42fdeea 100644
--- a/clang/test/Driver/split-debug.c
+++ b/clang/test/Driver/split-debug.c
@@ -11,7 +11,6 @@
 // NOINLINE-NOT: "-fsplit-dwarf-inlining"
 // SPLIT-NOT:  "-dumpdir"
 // SPLIT:      "-debug-info-kind=constructor"
-// SPLIT-SAME: "-ggnu-pubnames"
 // SPLIT-SAME: "-split-dwarf-file" "split-debug.dwo" "-split-dwarf-output" "split-debug.dwo"
 
 // RUN: %clang -### -c -target wasm32 -gsplit-dwarf -g %s 2>&1 | FileCheck %s --check-prefix=SPLIT

``````````

</details>


https://github.com/llvm/llvm-project/pull/82840