Provide gmlt-like inline scope information in the skeleton CU to facilitate symbolication without needing the .dwo files

Clang -gsplit-dwarf self-host -O0, binary increases by 0.0005%, -O2,
binary increases by 25%.

A large binary inside Google, split-dwarf, -O0, and other internal flags
(GDB index, etc) increases by 1.8%, optimized build is 35%.

The size impact may be somewhat greater in .o files (I haven't measured
that much - since the linked executable -O0 numbers seemed low enough)
due to relocations. These relocations could be removed if we taught the
llvm-symbolizer to handle indexed addressing in the .o file (GDB can't
cope with this just yet, but GDB won't be reading this info anyway).
Also debug_ranges could be shared between .o and .dwo, though ideally
debug_ranges would get a schema that could used index(+offset)
addressing, and move to the .dwo file, then we'd be back to sharing
addresses in the address pool again.

But for now, these sizes seem small enough to go ahead with this.

Verified that no other DW_TAGs are produced into the .o file other than
subprograms and inlined_subroutines.

llvm-svn: 221306

1 files changed, 25 insertions, 14 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index 580785588a7..a8f867a16c8 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -283,7 +283,7 @@ void DwarfCompileUnit::attachLowHighPC(DIE &D, const MCSymbol *Begin,
 // and DW_AT_high_pc attributes. If there are global variables in this
 // scope then create and insert DIEs for these variables.
 DIE &DwarfCompileUnit::updateSubprogramScopeDIE(DISubprogram SP) {
-  DIE *SPDie = getOrCreateSubprogramDIE(SP);
+  DIE *SPDie = getOrCreateSubprogramDIE(SP, includeMinimalInlineScopes());
 
   attachLowHighPC(*SPDie, DD->getFunctionBeginSym(), DD->getFunctionEndSym());
   if (!DD->getCurrentFunction()->getTarget().Options.DisableFramePointerElim(
@@ -291,7 +291,7 @@ DIE &DwarfCompileUnit::updateSubprogramScopeDIE(DISubprogram SP) {
     addFlag(*SPDie, dwarf::DW_AT_APPLE_omit_frame_ptr);
 
   // Only include DW_AT_frame_base in full debug info
-  if (getCUNode().getEmissionKind() != DIBuilder::LineTablesOnly) {
+  if (!includeMinimalInlineScopes()) {
     const TargetRegisterInfo *RI =
         Asm->TM.getSubtargetImpl()->getRegisterInfo();
     MachineLocation Location(RI->getFrameRegister(*Asm->MF));
@@ -341,10 +341,14 @@ void DwarfCompileUnit::constructScopeDIE(
     // null and the children will be added to the scope DIE.
     createScopeChildrenDIE(Scope, Children, &ChildScopeCount);
 
-    // There is no need to emit empty lexical block DIE.
-    for (const auto &E : DD->findImportedEntitiesForScope(DS))
-      Children.push_back(
-          constructImportedEntityDIE(DIImportedEntity(E.second)));
+    // Skip imported directives in gmlt-like data.
+    if (!includeMinimalInlineScopes()) {
+      // There is no need to emit empty lexical block DIE.
+      for (const auto &E : DD->findImportedEntitiesForScope(DS))
+        Children.push_back(
+            constructImportedEntityDIE(DIImportedEntity(E.second)));
+    }
+
     // If there are only other scopes as children, put them directly in the
     // parent instead, as this scope would serve no purpose.
     if (Children.size() == ChildScopeCount) {
@@ -576,7 +580,8 @@ void DwarfCompileUnit::constructSubprogramScopeDIE(LexicalScope *Scope) {
   // If we have more than one elements and the last one is null, it is a
   // variadic function.
   if (FnArgs.getNumElements() > 1 &&
-      !FnArgs.getElement(FnArgs.getNumElements() - 1))
+      !FnArgs.getElement(FnArgs.getNumElements() - 1) &&
+      !includeMinimalInlineScopes())
     ScopeDIE.addChild(make_unique<DIE>(dwarf::DW_TAG_unspecified_parameters));
 }
 
@@ -603,11 +608,13 @@ DwarfCompileUnit::constructAbstractSubprogramScopeDIE(LexicalScope *Scope) {
 
   DIE *ContextDIE;
 
+  if (includeMinimalInlineScopes())
+    ContextDIE = &getUnitDie();
   // Some of this is duplicated from DwarfUnit::getOrCreateSubprogramDIE, with
   // the important distinction that the DIDescriptor is not associated with the
   // DIE (since the DIDescriptor will be associated with the concrete DIE, if
   // any). It could be refactored to some common utility function.
-  if (DISubprogram SPDecl = SP.getFunctionDeclaration()) {
+  else if (DISubprogram SPDecl = SP.getFunctionDeclaration()) {
     ContextDIE = &getUnitDie();
     getOrCreateSubprogramDIE(SPDecl);
   } else
@@ -619,7 +626,7 @@ DwarfCompileUnit::constructAbstractSubprogramScopeDIE(LexicalScope *Scope) {
       &createAndAddDIE(dwarf::DW_TAG_subprogram, *ContextDIE, DIDescriptor());
   applySubprogramAttributesToDefinition(SP, *AbsDef);
 
-  if (getCUNode().getEmissionKind() != DIBuilder::LineTablesOnly)
+  if (!includeMinimalInlineScopes())
     addUInt(*AbsDef, dwarf::DW_AT_inline, None, dwarf::DW_INL_inlined);
   if (DIE *ObjectPointer = createAndAddScopeChildren(Scope, *AbsDef))
     addDIEEntry(*AbsDef, dwarf::DW_AT_object_pointer, *ObjectPointer);
@@ -660,7 +667,7 @@ void DwarfCompileUnit::finishSubprogramDefinition(DISubprogram SP) {
       // If this subprogram has an abstract definition, reference that
       addDIEEntry(*D, dwarf::DW_AT_abstract_origin, *AbsSPDIE);
   } else {
-    if (!D && getCUNode().getEmissionKind() != DIBuilder::LineTablesOnly)
+    if (!D && !includeMinimalInlineScopes())
       // Lazily construct the subprogram if we didn't see either concrete or
       // inlined versions during codegen. (except in -gmlt ^ where we want
       // to omit these entirely)
@@ -703,7 +710,7 @@ void DwarfCompileUnit::emitHeader(const MCSymbol *ASectionSym) const {
 /// addGlobalName - Add a new global name to the compile unit.
 void DwarfCompileUnit::addGlobalName(StringRef Name, DIE &Die,
                                      DIScope Context) {
-  if (getCUNode().getEmissionKind() == DIBuilder::LineTablesOnly)
+  if (includeMinimalInlineScopes())
     return;
   std::string FullName = getParentContextString(Context) + Name.str();
   GlobalNames[FullName] = &Die;
@@ -712,7 +719,7 @@ void DwarfCompileUnit::addGlobalName(StringRef Name, DIE &Die,
 /// Add a new global type to the unit.
 void DwarfCompileUnit::addGlobalType(DIType Ty, const DIE &Die,
                                      DIScope Context) {
-  if (getCUNode().getEmissionKind() == DIBuilder::LineTablesOnly)
+  if (includeMinimalInlineScopes())
     return;
   std::string FullName = getParentContextString(Context) + Ty.getName().str();
   GlobalTypes[FullName] = &Die;
@@ -838,12 +845,16 @@ void DwarfCompileUnit::applySubprogramAttributesToDefinition(DISubprogram SP,
                                                              DIE &SPDie) {
   DISubprogram SPDecl = SP.getFunctionDeclaration();
   DIScope Context = resolve(SPDecl ? SPDecl.getContext() : SP.getContext());
-  applySubprogramAttributes(SP, SPDie, getCUNode().getEmissionKind() ==
-                                           DIBuilder::LineTablesOnly);
+  applySubprogramAttributes(SP, SPDie, includeMinimalInlineScopes());
   addGlobalName(SP.getName(), SPDie, Context);
 }
 
 bool DwarfCompileUnit::isDwoUnit() const {
   return DD->useSplitDwarf() && Skeleton;
 }
+
+bool DwarfCompileUnit::includeMinimalInlineScopes() const {
+  return getCUNode().getEmissionKind() == DIBuilder::LineTablesOnly ||
+         (DD->useSplitDwarf() && !Skeleton);
+}
 } // end llvm namespace