[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/CodeGen/PowerPC/dbg.ll b/llvm/test/CodeGen/PowerPC/dbg.ll
index 68671c5be0f..94c8a88316a 100644
--- a/llvm/test/CodeGen/PowerPC/dbg.ll
+++ b/llvm/test/CodeGen/PowerPC/dbg.ll
@@ -17,10 +17,9 @@ declare void @llvm.dbg.value(metadata, i64, metadata, metadata) nounwind readnon
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!22}
 
-!0 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.1", isOptimized: true, emissionKind: FullDebug, file: !21, enums: !1, retainedTypes: !1, subprograms: !3, globals: !1, imports: !1)
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang version 3.1", isOptimized: true, emissionKind: FullDebug, file: !21, enums: !1, retainedTypes: !1, globals: !1, imports: !1)
 !1 = !{}
-!3 = !{!5}
-!5 = distinct !DISubprogram(name: "main", line: 1, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, file: !21, scope: null, type: !7, variables: !13)
+!5 = distinct !DISubprogram(name: "main", line: 1, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, unit: !0, file: !21, scope: null, type: !7, variables: !13)
 !6 = !DIFile(filename: "dbg.c", directory: "/src")
 !7 = !DISubroutineType(types: !8)
 !8 = !{!9, !9, !10}