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, 2 deletions

diff --git a/llvm/lib/CodeGen/LiveDebugVariables.cpp b/llvm/lib/CodeGen/LiveDebugVariables.cpp
index 6559d8df1a2..654328714bc 100644
--- a/llvm/lib/CodeGen/LiveDebugVariables.cpp
+++ b/llvm/lib/CodeGen/LiveDebugVariables.cpp
@@ -761,7 +761,7 @@ static void removeDebugValues(MachineFunction &mf) {
 bool LiveDebugVariables::runOnMachineFunction(MachineFunction &mf) {
   if (!EnableLDV)
     return false;
-  if (!FunctionDIs.count(mf.getFunction())) {
+  if (!mf.getFunction()->getSubprogram()) {
     removeDebugValues(mf);
     return false;
   }
@@ -1045,7 +1045,6 @@ void LiveDebugVariables::emitDebugValues(VirtRegMap *VRM) {
 }
 
 bool LiveDebugVariables::doInitialization(Module &M) {
-  FunctionDIs = makeSubprogramMap(M);
   return Pass::doInitialization(M);
 }