[PR27284] Reverse the ownership between DICompileUnit and DISubprogram.

Currently each Function points to a DISubprogram and DISubprogram has a
scope field. For member functions the scope is a DICompositeType. DIScopes
point to the DICompileUnit to facilitate type uniquing.

Distinct DISubprograms (with isDefinition: true) are not part of the type
hierarchy and cannot be uniqued. This change removes the subprograms
list from DICompileUnit and instead adds a pointer to the owning compile
unit to distinct DISubprograms. This would make it easy for ThinLTO to
strip unneeded DISubprograms and their transitively referenced debug info.

Motivation
----------

Materializing DISubprograms is currently the most expensive operation when
doing a ThinLTO build of clang.

We want the DISubprogram to be stored in a separate Bitcode block (or the
same block as the function body) so we can avoid having to expensively
deserialize all DISubprograms together with the global metadata. If a
function has been inlined into another subprogram we need to store a
reference the block containing the inlined subprogram.

Attached to https://llvm.org/bugs/show_bug.cgi?id=27284 is a python script
that updates LLVM IR testcases to the new format.

http://reviews.llvm.org/D19034
<rdar://problem/25256815>

llvm-svn: 266446

1 files changed, 2 insertions, 3 deletions

diff --git a/llvm/test/DebugInfo/Generic/namespace_function_definition.ll b/llvm/test/DebugInfo/Generic/namespace_function_definition.ll
index 5d23d51144d..283761314a4 100644
--- a/llvm/test/DebugInfo/Generic/namespace_function_definition.ll
+++ b/llvm/test/DebugInfo/Generic/namespace_function_definition.ll
@@ -30,11 +30,10 @@ attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointe
 !llvm.module.flags = !{!8, !9}
 !llvm.ident = !{!10}
 
-!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, producer: "clang version 3.5.0 ", isOptimized: false, emissionKind: FullDebug, file: !1, enums: !2, retainedTypes: !2, subprograms: !3, globals: !2, imports: !2)
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, producer: "clang version 3.5.0 ", isOptimized: false, emissionKind: FullDebug, file: !1, enums: !2, retainedTypes: !2, globals: !2, imports: !2)
 !1 = !DIFile(filename: "namespace_function_definition.cpp", directory: "/tmp/dbginfo")
 !2 = !{}
-!3 = !{!4}
-!4 = distinct !DISubprogram(name: "func", linkageName: "_ZN2ns4funcEv", line: 2, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: false, scopeLine: 2, file: !1, scope: !5, type: !6, variables: !2)
+!4 = distinct !DISubprogram(name: "func", linkageName: "_ZN2ns4funcEv", line: 2, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: false, unit: !0, scopeLine: 2, file: !1, scope: !5, type: !6, variables: !2)
 !5 = !DINamespace(name: "ns", line: 1, file: !1, scope: null)
 !6 = !DISubroutineType(types: !7)
 !7 = !{null}