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, 4 insertions, 18 deletions

diff --git a/llvm/lib/IR/DebugInfo.cpp b/llvm/lib/IR/DebugInfo.cpp
index b22ba53645d..a2443becdd0 100644
--- a/llvm/lib/IR/DebugInfo.cpp
+++ b/llvm/lib/IR/DebugInfo.cpp
@@ -300,6 +300,10 @@ bool DebugInfoFinder::addScope(DIScope *Scope) {
 
 bool llvm::stripDebugInfo(Function &F) {
   bool Changed = false;
+  if (F.getSubprogram()) {
+    Changed = true;
+    F.setSubprogram(nullptr);
+  }
   for (BasicBlock &BB : F) {
     for (Instruction &I : BB) {
       if (I.getDebugLoc()) {
@@ -359,21 +363,3 @@ unsigned llvm::getDebugMetadataVersionFromModule(const Module &M) {
     return Val->getZExtValue();
   return 0;
 }
-
-DenseMap<const llvm::Function *, DISubprogram *>
-llvm::makeSubprogramMap(const Module &M) {
-  DenseMap<const Function *, DISubprogram *> R;
-
-  NamedMDNode *CU_Nodes = M.getNamedMetadata("llvm.dbg.cu");
-  if (!CU_Nodes)
-    return R;
-
-  for (MDNode *N : CU_Nodes->operands()) {
-    auto *CUNode = cast<DICompileUnit>(N);
-    for (auto *SP : CUNode->getSubprograms()) {
-      if (Function *F = SP->getFunction())
-        R.insert(std::make_pair(F, SP));
-    }
-  }
-  return R;
-}