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, 2 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp b/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
index bdd1b61f9b2..0e05129b526 100644
--- a/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
+++ b/llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
@@ -95,7 +95,6 @@ namespace {
     bool doInitialization(CallGraph &CG) override;
     /// The maximum number of elements to expand, or 0 for unlimited.
     unsigned maxElements;
-    DenseMap<const Function *, DISubprogram *> FunctionDIs;
   };
 }
 
@@ -732,15 +731,8 @@ CallGraphNode *ArgPromotion::DoPromotion(Function *F,
   NF->copyAttributesFrom(F);
 
   // Patch the pointer to LLVM function in debug info descriptor.
-  auto DI = FunctionDIs.find(F);
-  if (DI != FunctionDIs.end()) {
-    DISubprogram *SP = DI->second;
-    SP->replaceFunction(NF);
-    // Ensure the map is updated so it can be reused on subsequent argument
-    // promotions of the same function.
-    FunctionDIs.erase(DI);
-    FunctionDIs[NF] = SP;
-  }
+  NF->setSubprogram(F->getSubprogram());
+  F->setSubprogram(nullptr);
 
   DEBUG(dbgs() << "ARG PROMOTION:  Promoting to:" << *NF << "\n"
         << "From: " << *F);
@@ -1023,6 +1015,5 @@ CallGraphNode *ArgPromotion::DoPromotion(Function *F,
 }
 
 bool ArgPromotion::doInitialization(CallGraph &CG) {
-  FunctionDIs = makeSubprogramMap(CG.getModule());
   return CallGraphSCCPass::doInitialization(CG);
 }