[CLANG][DWARF] Do not emit -ggnu-pubnames for split dwarf version 5.

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:
6586452#diff-bac41c71569f27df21a843bcd74d2e604ed508afbdf141777761dfb545c5d228

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

Author: ayermolo

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4478,14 +4478,20 @@ renderDebugOptions(const ToolChain &TC, const Driver &D, const llvm::Triple &T,
       Args.getLastArg(options::OPT_ggnu_pubnames, options::OPT_gno_gnu_pubnames,
                       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)))
+      (PubnamesArg && checkDebugInfoOption(PubnamesArg, Args, D, TC))) {
+    const bool OptionSet =
+        (PubnamesArg &&
+         (PubnamesArg->getOption().matches(options::OPT_gpubnames) ||
+          PubnamesArg->getOption().matches(options::OPT_ggnu_pubnames)));
+    if ((DebuggerTuning != llvm::DebuggerKind::LLDB || OptionSet) &&
+        (!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"
                             : "-ggnu-pubnames");
+  }
   const auto *SimpleTemplateNamesArg =
       Args.getLastArg(options::OPT_gsimple_template_names,
                       options::OPT_gno_simple_template_names);

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
@@ -124,3 +123,13 @@
 // G1_NOSPLIT: "-debug-info-kind=line-tables-only"
 // G1_NOSPLIT-NOT: "-split-dwarf-file"
 // G1_NOSPLIT-NOT: "-split-dwarf-output"
+
+/// Do not generate -ggnu-pubnames for -glldb
+// RUN: %clang -### -c -target x86_64 -gsplit-dwarf -g -glldb %s 2>&1 | FileCheck %s --check-prefixes=GLLDBSPLIT
+
+// GLLDBSPLIT-NOT: "-ggnu-pubnames"
+
+/// Generate -ggnu-pubnames for -glldb when it is explicitly enabled
+// RUN: %clang -### -c -target x86_64 -gsplit-dwarf -g -glldb -ggnu-pubnames %s 2>&1 | FileCheck %s --check-prefixes=GLLDBSPLIT2
+
+// GLLDBSPLIT2: "-ggnu-pubnames"