[DebugInfo] Emit DW_AT_inline under -g1/-gmlt

[zequanwu]

Summary

This allows some tools (e.g. dump_syms) to rely on DW_AT_inline to determine if a DW_TAG_subprogram is inlined or not.

Tested for building chrome, the .debug_info size increased 1.4% under -g1 with this change with dwarf4, and only 1.5% increase in .debug_abbrev with dwarf 5.

Dwarf4 size changes:

   FILE SIZE        VM SIZE
--------------  --------------
 +1.4% +3.39Mi  [ = ]       0    .debug_info
 +1.0% +53.9Ki  [ = ]       0    .debug_abbrev
 -0.0%      -2  [ = ]       0    .debug_str
 +0.4% +3.45Mi  [ = ]       0    TOTAL

Dwarf5 size changes:

   FILE SIZE        VM SIZE
--------------  --------------
 +1.5% +86.3Ki  [ = ]       0    .debug_abbrev
 +0.0% +86.3Ki  [ = ]       0    TOTAL

[dblaikie]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

1108–1112

Could these be collapsed down into:

ContextCU->addUInt(*AbsDef, dwarf::DW_AT_inline, (DD->getDwarfVersion() <= 4 ? std::optional<dwarf::Form>() : dwarf::DW_FORM_implicit_const), dwarf::DW_INL_inlined);

? (and/or is there a particular reason one of these is UInt and the other is SInt?

llvm/test/DebugInfo/Inputs/gmlt.ll

37–41

This comment points to an alternate direction at least for DWARFv5 - if that's of interest.

[zequanwu]

Address comment.

[zequanwu]

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

1108–1112

Changed to one addSInt, as addUInt doesn't allow dwarf::DW_FORM_implicit_const.

llvm/test/DebugInfo/Inputs/gmlt.ll

37–41

Yeah, looks like could save some spaces by replacing all DW_AT_abstract_origin with a string index.

[dblaikie]

Looks good, thanks!

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

else if (auto *SPDecl = SP->getDeclaration()) {
     // subprogram in the same CU.
     ContextCU = DD->lookupCU(ContextDIE->getUnitDie());
   }
 
   // Passing null as the associated node because the abstract definition
   // shouldn't be found by lookup.
   AbsDef = &ContextCU->createAndAddDIE(dwarf::DW_TAG_subprogram, *ContextDIE, nullptr);
   ContextCU->applySubprogramAttributesToDefinition(SP, *AbsDef);
-
-  if (!ContextCU->includeMinimalInlineScopes())
-    ContextCU->addUInt(*AbsDef, dwarf::DW_AT_inline, None, dwarf::DW_INL_inlined);
+  ContextCU->addSInt(*AbsDef, dwarf::DW_AT_inline,
+                     DD->getDwarfVersion() <= 4 ? Optional<dwarf::Form>()
+                                                : dwarf::DW_FORM_implicit_const,
+                     dwarf::DW_INL_inlined);
   if (DIE *ObjectPointer = ContextCU->createAndAddScopeChildren(Scope, *AbsDef))
     ContextCU->addDIEEntry(*AbsDef, dwarf::DW_AT_object_pointer, *ObjectPointer);
 }
 
 bool DwarfCompileUnit::useGNUAnalogForDwarf5Feature() const {
   return DD->getDwarfVersion() == 4 && !DD->tuneForLLDB();
 }
 
 dwarf::Tag DwarfCompileUnit::getDwarf5OrGNUTag(dwarf::Tag Tag) const {

llvm/test/DebugInfo/Inputs/gmlt.ll

 ; DARWIN:  DW_TAG_subprogram
 ; DARWIN-NOT: DW_TAG
 ; Can't check the abstract_origin value across the DARWIN/CHECK checking and
 ; ordering, so don't bother - just trust me, it refers to f3 down there.
 ; DARWIN:    DW_AT_abstract_origin
 ; DARWIN-NOT: {{DW_TAG|NULL}}
 
 
 ; FIXME: Emitting separate abstract definitions is inefficient when we could
 ; just attach the DW_AT_name to the inlined_subroutine directly. Except that
 ; would produce many string relocations. Implement string indexing in the
 ; skeleton CU to address the relocation problem, then remove abstract
 ; definitions from -gmlt here.
 
 ; CHECK: DW_TAG_subprogram
 ; CHECK-NEXT:     DW_AT_name {{.*}} "f3"
-
-; FIXME: We don't really need DW_AT_inline, consumers can ignore this due to
-; the absence of high_pc/low_pc/ranges and know that they just need it for
-; retrieving the name of a concrete inlined instance
-
-; CHECK-NOT: {{DW_TAG|DW_AT|NULL}}
+; CHECK-NEXT:     DW_AT_inline
 
 ; Check that we only provide the minimal attributes on a subprogram to save space.
 ; CHECK:   DW_TAG_subprogram
 ; CHECK-NEXT:     DW_AT_low_pc
 ; CHECK-NEXT:     DW_AT_high_pc
 ; CHECK-NEXT:     DW_AT_name
 ; CHECK-NOT: {{DW_TAG|DW_AT}}
 ; CHECK:     DW_TAG_inlined_subroutine

llvm/test/DebugInfo/X86/fission-inline.ll

 ; descriptions of subprograms with inlined scopes.
 
 ; FIXME: Once tools support indexed addresses in the skeleton CU, we should use
 ; those (DW_FORM_addr would become DW_FORM_GNU_addr_index below) since those
 ; addresses will already be in the address pool anyway.
 
 ; CHECK:      DW_TAG_subprogram
 ; CHECK-NEXT:   DW_AT_name {{.*}} "f2<int>"
-; CHECK-NOT: DW_
+; CHECK-NEXT:   DW_AT_inline
 ; CHECK:      DW_TAG_subprogram
 ; CHECK-NEXT:   DW_AT_low_pc [DW_FORM_addr]
 ; CHECK-NEXT:   DW_AT_high_pc
 ; CHECK-NEXT:   DW_AT_name {{.*}} "f3"
 ; CHECK-NOT: {{DW_|NULL}}
 ; CHECK:        DW_TAG_inlined_subroutine
 ; CHECK-NEXT:     DW_AT_abstract_origin {{.*}} "f2<int>"
 ; CHECK-NEXT:     DW_AT_ranges