[DEBUGINFO] Add flag -no-dwarf-gnu-pub-sections to disable gnu pub sections.

[ABataev]

Summary

Added a flag -no-dwarf-gnu-pub-sections, which allows to disable
emission of gnu public sections.

[dblaikie]

What's the use-case/motivation? Should this be an IR feature (on a per-CU
basis, so that LTO can correctly respect some CUs requesting this feature,
and some disabling it)

[ABataev]

Fixed processing only for dwarf pub sections.

[echristo]

In D44385#1034799, @dblaikie wrote:

What's the use-case/motivation? Should this be an IR feature (on a per-CU
basis, so that LTO can correctly respect some CUs requesting this feature,
and some disabling it)

Right now the idea is that we're going to want to turn off certain kinds of sections for nvptx based assembly (same as the other patch). I think we can possibly come up with dwarf/elf ways to encode this data, but in the short term let's get asm printer (and use a flag to set it up piece by piece testable) and then we can try to figure out ways to actually get the data out in the long term.

I'm going to accept this for now as I had an offline conversation with Dave earlier about this. If there's any review I think it can be post-commit here.

Thanks all!

-eric

lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

 }
 
 bool DwarfCompileUnit::hasDwarfPubSections() const {
   // Opting in to GNU Pubnames/types overrides the default to ensure these are
   // generated for things like Gold's gdb_index generation.
   if (CUNode->getGnuPubnames())
     return true;
 
-  return DD->tuneForGDB() && !includeMinimalInlineScopes();
+  return DD->tuneForGDB() && DD->usePubSections() &&
+         !includeMinimalInlineScopes();
 }
 
 /// addGlobalName - Add a new global name to the compile unit.
 void DwarfCompileUnit::addGlobalName(StringRef Name, const DIE &Die,
                                      const DIScope *Context) {
   if (!hasDwarfPubSections())
     return;
   std::string FullName = getParentContextString(Context) + Name.str();

lib/CodeGen/AsmPrinter/DwarfDebug.h

class DwarfDebug : public DebugHandlerBase {
   bool UseDWARF2Bitfields;
 
   /// Whether to emit all linkage names, or just abstract subprograms.
   bool UseAllLinkageNames;
 
   /// Use inlined strings.
   bool UseInlineStrings = false;
 
+  /// Whether to emit DWARF pub sections or not.
+  bool UsePubSections = true;
+
   /// DWARF5 Experimental Options
   /// @{
   bool HasDwarfAccelTables;
   bool HasAppleExtensionAttributes;
   bool HasSplitDwarf;
 
   /// Whether to generate the DWARF v5 string offsets table.
   /// It consists of a series of contributions, each preceded by a header.
public:
 
   /// Returns whether to use the DWARF2 format for bitfields instyead of the
   /// DWARF4 format.
   bool useDWARF2Bitfields() const { return UseDWARF2Bitfields; }
 
   /// Returns whether to use inline strings.
   bool useInlineStrings() const { return UseInlineStrings; }
 
+  /// Returns whether GNU oub sections should be emitted.
+  bool usePubSections() const { return UsePubSections; }
+
   // Experimental DWARF5 features.
 
   /// Returns whether or not to emit tables that dwarf consumers can
   /// use to accelerate lookup.
   bool useDwarfAccelTables() const { return HasDwarfAccelTables; }
 
   bool useAppleExtensionAttributes() const {
     return HasAppleExtensionAttributes;

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

 static cl::opt<DefaultOnOff>
 DwarfInlinedStrings("dwarf-inlined-strings", cl::Hidden,
                  cl::desc("Use inlined strings rather than string section."),
                  cl::values(clEnumVal(Default, "Default for platform"),
                             clEnumVal(Enable, "Enabled"),
                             clEnumVal(Disable, "Disabled")),
                  cl::init(Default));
 
+static cl::opt<bool>
+    NoDwarfPubSections("no-dwarf-pub-sections", cl::Hidden,
+                       cl::desc("Disable emission of DWARF pub sections."),
+                       cl::init(false));
+
 enum LinkageNameOption {
   DefaultLinkageNames,
   AllLinkageNames,
   AbstractLinkageNames
 };
 
 static cl::opt<LinkageNameOption>
     DwarfLinkageNames("dwarf-linkage-names", cl::Hidden,
else
     UseAllLinkageNames = DwarfLinkageNames == AllLinkageNames;
 
   unsigned DwarfVersionNumber = Asm->TM.Options.MCOptions.DwarfVersion;
   unsigned DwarfVersion = DwarfVersionNumber ? DwarfVersionNumber
                                     : MMI->getModule()->getDwarfVersion();
   // Use dwarf 4 by default if nothing is requested.
   DwarfVersion = DwarfVersion ? DwarfVersion : dwarf::DWARF_VERSION;
 
+  UsePubSections = !NoDwarfPubSections;
+
   // Work around a GDB bug. GDB doesn't support the standard opcode;
   // SCE doesn't support GNU's; LLDB prefers the standard opcode, which
   // is defined as of DWARF 3.
   // See GDB bug 11616 - DW_OP_form_tls_address is unimplemented
   // https://sourceware.org/bugzilla/show_bug.cgi?id=11616
   UseGNUTLSOpcode = tuneForGDB() || DwarfVersion < 3;
 
   // GDB does not fully support the DWARF 4 representation for bitfields.

test/DebugInfo/X86/no-public-sections.ll

+; RUN: llc -mtriple=x86_64-pc-linux-gnu -debugger-tune=gdb -filetype=asm < %s -no-dwarf-pub-sections | FileCheck %s --check-prefix=DISABLED
+; RUN: llc -mtriple=x86_64-pc-linux-gnu -debugger-tune=gdb -filetype=asm < %s | FileCheck %s
+
+; DISABLED-NOT: {{.debug_pubnames|.debug_pubtypes}}
+; CHECK-DAG: .section .debug_pubnames
+; CHECK-DAG: .section .debug_pubtypes
+
+%struct.bar = type { %"struct.ns::foo" }
+%"struct.ns::foo" = type { i8 }
+
+@b = global %struct.bar zeroinitializer, align 1, !dbg !0
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!11, !12}
+!llvm.ident = !{!13}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "b", scope: !2, file: !3, line: 8, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5, gnuPubnames: false)
+!3 = !DIFile(filename: "type.cpp", directory: "/tmp/dbginfo")
+!4 = !{}
+!5 = !{!0}
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "bar", file: !3, line: 5, size: 8, elements: !7, identifier: "_ZTS3bar")
+!7 = !{!8}
+!8 = !DIDerivedType(tag: DW_TAG_member, name: "f", scope: !6, file: !3, line: 6, baseType: !9, size: 8)
+!9 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "foo", scope: !10, file: !3, line: 2, size: 8, elements: !4, identifier: "_ZTSN2ns3fooE")
+!10 = !DINamespace(name: "ns", scope: null)
+!11 = !{i32 2, !"Dwarf Version", i32 4}
+!12 = !{i32 2, !"Debug Info Version", i32 3}
+!13 = !{!"clang"}
+