[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>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266446 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 3 deletions

diff --git a/test/Bitcode/debug-loc-again.ll b/test/Bitcode/debug-loc-again.ll
index de26dd4b593..3bfbd1ff30b 100644
--- a/test/Bitcode/debug-loc-again.ll
+++ b/test/Bitcode/debug-loc-again.ll
@@ -30,8 +30,7 @@ entry:
 !llvm.dbg.cu = !{!1}
 
 !0 = !{i32 2, !"Debug Info Version", i32 3}
-!1 = distinct !DICompileUnit(language: DW_LANG_C99, file: !DIFile(filename: "f", directory: "/d"),
-                             subprograms: !{!2})
-!2 = distinct !DISubprogram(name: "foo")
+!1 = distinct !DICompileUnit(language: DW_LANG_C99, file: !DIFile(filename: "f", directory: "/d"))
+!2 = distinct !DISubprogram(name: "foo", unit: !1)
 !3 = !DILocation(line: 1, scope: !2)
 !4 = !DILocation(line: 2, scope: !2)