DI: Reverse direction of subprogram -> function edge.

Previously, subprograms contained a metadata reference to the function they
described. Because most clients need to get or set a subprogram for a given
function rather than the other way around, this created unneeded inefficiency.

For example, many passes needed to call the function llvm::makeSubprogramMap()
to build a mapping from functions to subprograms, and the IR linker needed to
fix up function references in a way that caused quadratic complexity in the IR
linking phase of LTO.

This change reverses the direction of the edge by storing the subprogram as
function-level metadata and removing DISubprogram's function field.

Since this is an IR change, a bitcode upgrade has been provided.

Fixes PR23367. An upgrade script for textual IR for out-of-tree clients is
attached to the PR.

Differential Revision: http://reviews.llvm.org/D14265

llvm-svn: 252219

1 files changed, 1 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Utils/CloneFunction.cpp b/llvm/lib/Transforms/Utils/CloneFunction.cpp
index 86f7068..bd6cd3a 100644
--- a/llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ b/llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -188,11 +188,9 @@ static void CloneDebugInfoMetadata(Function *NewFunc, const Function *OldFunc,
   const DISubprogram *OldSubprogramMDNode = FindSubprogram(OldFunc, Finder);
   if (!OldSubprogramMDNode) return;
 
-  // Ensure that OldFunc appears in the map.
-  // (if it's already there it must point to NewFunc anyway)
-  VMap[OldFunc] = NewFunc;
   auto *NewSubprogram =
       cast<DISubprogram>(MapMetadata(OldSubprogramMDNode, VMap));
+  NewFunc->setSubprogram(NewSubprogram);
 
   for (auto *CU : Finder.compile_units()) {
     auto Subprograms = CU->getSubprograms();