[DebugInfo][DwarfDebug] Separate creation and population of abstract subprogram DIEs (#159104)

With this change, construction of abstract subprogram DIEs is split in
two stages/functions:
creation of DIE (in DwarfCompileUnit::getOrCreateAbstractSubprogramDIE)
and its population with children (in
DwarfCompileUnit::constructAbstractSubprogramScopeDIE).
With that, abstract subprograms can be created/referenced from
DwarfDebug::beginModule, which should solve the issue with static local
variables DIE creation of inlined functons with optimized-out
definitions. It fixes https://github.com/llvm/llvm-project/issues/29985.

LexicalScopes class now stores mapping from DISubprograms to their
corresponding llvm::Function's. It is supposed to be built before
processing of each function (so, now LexicalScopes class has a method
for "module initialization" alongside the method for "function
initialization"). It is used by DwarfCompileUnit to determine whether a
DISubprogram needs an abstract DIE before DwarfDebug::beginFunction is
invoked.

DwarfCompileUnit::getOrCreateSubprogramDIE method is added, which can
create an abstract or a concrete DIE for a subprogram. It accepts
llvm::Function* argument to determine whether a concrete DIE must be
created.

This is a temporary fix for
https://github.com/llvm/llvm-project/issues/29985. Ideally, it will be
fixed by moving global variables and types emission to
DwarfDebug::endModule (https://reviews.llvm.org/D144007,
https://reviews.llvm.org/D144005).

Some code proposed by Ellis Hoag <ellis.sparky.hoag@gmail.com> in
https://github.com/llvm/llvm-project/pull/90523 was taken for this
commit.

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
index 0f3ff98..d98d180 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DebugHandlerBase.cpp
@@ -105,6 +105,8 @@ DebugHandlerBase::~DebugHandlerBase() = default;
 void DebugHandlerBase::beginModule(Module *M) {
   if (M->debug_compile_units().empty())
     Asm = nullptr;
+  else
+    LScopes.initialize(*M);
 }
 
 // Each LexicalScope has first instruction and last instruction to mark
@@ -269,7 +271,7 @@ void DebugHandlerBase::beginFunction(const MachineFunction *MF) {
 
   // Grab the lexical scopes for the function, if we don't have any of those
   // then we're not going to be able to do anything.
-  LScopes.initialize(*MF);
+  LScopes.scanFunction(*MF);
   if (LScopes.empty()) {
     beginFunctionImpl(MF);
     return;