[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

2 files changed, 4 insertions, 6 deletions

diff --git a/llvm/test/Transforms/LoopSimplify/dbg-loc.ll b/llvm/test/Transforms/LoopSimplify/dbg-loc.ll
index 23a60481db6..702a1ad16af 100644
--- a/llvm/test/Transforms/LoopSimplify/dbg-loc.ll
+++ b/llvm/test/Transforms/LoopSimplify/dbg-loc.ll
@@ -81,7 +81,7 @@ eh.resume:                                        ; preds = %catch
 !3 = !{}
 !4 = !DISubroutineType(types: !3)
 !5 = !DIFile(filename: "Vector.h", directory: "/tmp")
-!6 = distinct !DISubprogram(name: "destruct", scope: !5, file: !5, line: 71, type: !4, isLocal: false, isDefinition: true, scopeLine: 72, flags: DIFlagPrototyped, isOptimized: false, variables: !3)
+!6 = distinct !DISubprogram(name: "destruct", scope: !5, file: !5, line: 71, type: !4, isLocal: false, isDefinition: true, scopeLine: 72, flags: DIFlagPrototyped, isOptimized: false, unit: !14, variables: !3)
 !7 = !DILocation(line: 73, column: 38, scope: !6)
 !8 = !DILocation(line: 73, column: 13, scope: !6)
 !9 = !DILocation(line: 73, column: 27, scope: !6)
@@ -92,5 +92,4 @@ eh.resume:                                        ; preds = %catch
 !14 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang",
                              file: !5,
                              isOptimized: true, flags: "-O2",
-                             splitDebugFilename: "abc.debug", emissionKind: 2,
-                             subprograms: !{!6})
+                             splitDebugFilename: "abc.debug", emissionKind: 2)
diff --git a/llvm/test/Transforms/LoopSimplify/single-backedge.ll b/llvm/test/Transforms/LoopSimplify/single-backedge.ll
index 40e903ea570..16d29e4915b 100644
--- a/llvm/test/Transforms/LoopSimplify/single-backedge.ll
+++ b/llvm/test/Transforms/LoopSimplify/single-backedge.ll
@@ -31,7 +31,7 @@ BE2:    ; preds = %n br label %Loop
 !2 = !{}
 !3 = !DISubroutineType(types: !2)
 !4 = !DIFile(filename: "atomic.cpp", directory: "/tmp")
-!5 = distinct !DISubprogram(name: "test", scope: !4, file: !4, line: 99, type: !3, isLocal: false, isDefinition: true, scopeLine: 100, flags: DIFlagPrototyped, isOptimized: false, variables: !2)
+!5 = distinct !DISubprogram(name: "test", scope: !4, file: !4, line: 99, type: !3, isLocal: false, isDefinition: true, scopeLine: 100, flags: DIFlagPrototyped, isOptimized: false, unit: !12, variables: !2)
 !6 = !DILocation(line: 100, column: 1, scope: !5)
 !7 = !DILocation(line: 101, column: 1, scope: !5)
 !8 = !DILocation(line: 102, column: 1, scope: !5)
@@ -41,5 +41,4 @@ BE2:    ; preds = %n br label %Loop
 !12 = distinct !DICompileUnit(language: DW_LANG_C99, producer: "clang",
                              file: !4,
                              isOptimized: true, flags: "-O2",
-                             splitDebugFilename: "abc.debug", emissionKind: 2,
-                             subprograms: !{!5})
+                             splitDebugFilename: "abc.debug", emissionKind: 2)