[PATCH] D18477: Drop debug info for DISubprograms that are not referenced by anything

[Duncan P. N. Exon Smith via llvm-commits]

> On 2016-Apr-06, at 17:09, Adrian Prantl <aprantl at apple.com> wrote:
> 
> aprantl added a comment.
> 
> Ping.
> 
> 
> http://reviews.llvm.org/D18477

There's something I don't quite understand in the DwarfDebug.cpp which
I point out below.  Heading out on vacation, so I'm happy to defer to
Eric/David/you/etc. if it makes sense (LGTM once others are happy).

> Index: lib/CodeGen/AsmPrinter/DwarfDebug.cpp
> ===================================================================
> --- lib/CodeGen/AsmPrinter/DwarfDebug.cpp
> +++ lib/CodeGen/AsmPrinter/DwarfDebug.cpp
> @@ -527,29 +527,10 @@
>  
>  void DwarfDebug::finishSubprogramDefinitions() {
>    for (const auto &P : SPMap)
> -    forBothCUs(*P.second, [&](DwarfCompileUnit &CU) {
> -      CU.finishSubprogramDefinition(cast<DISubprogram>(P.first));
> -    });
> -}
> -
> -// Collect info for variables that were optimized out.
> -void DwarfDebug::collectDeadVariables() {
> -  const Module *M = MMI->getModule();
> -
> -  if (NamedMDNode *CU_Nodes = M->getNamedMetadata("llvm.dbg.cu")) {
> -    for (MDNode *N : CU_Nodes->operands()) {
> -      auto *TheCU = cast<DICompileUnit>(N);
> -      // Construct subprogram DIE and add variables DIEs.
> -      DwarfCompileUnit *SPCU =
> -          static_cast<DwarfCompileUnit *>(CUMap.lookup(TheCU));
> -      assert(SPCU && "Unable to find Compile Unit!");
> -      for (auto *SP : TheCU->getSubprograms()) {
> -        if (ProcessedSPNodes.count(SP) != 0)
> -          continue;
> -        SPCU->collectDeadVariables(SP);
> -      }
> -    }
> -  }
> +    if (ProcessedSPNodes.count(P.first))
> +      forBothCUs(*P.second, [&](DwarfCompileUnit &CU) {
> +          CU.finishSubprogramDefinition(cast<DISubprogram>(P.first));
> +        });

^ remember this...

>  }
>  
>  void DwarfDebug::finalizeModuleInfo() {
> @@ -559,9 +540,6 @@
>  
>    finishVariableDefinitions();
>  
> -  // Collect info for variables that were optimized out.
> -  collectDeadVariables();
> -
>    // Handle anything that needs to be done on a per-unit basis after
>    // all other generation.
>    for (const auto &P : CUMap) {
> @@ -1121,6 +1099,10 @@
>      PrevCU = nullptr;
>      CurFn = nullptr;
>      DebugHandlerBase::endFunction(MF);
> +    // Mark functions with no debug info on any instructions, but a
> +    // valid DISubprogram as processed.
> +    if (auto *SP = MF->getFunction()->getSubprogram())
> +      ProcessedSPNodes.insert(SP);

Why do you want to run the above code for these subprograms?
Don't you want to skip them entirely?

>      return;
>    }
>  
>