[llvm] r204790 - Fix PR19239 - Add support for generating debug info for functions without lexical scopes and/or debug info at all

[David Blaikie]

On Wed, Mar 26, 2014 at 2:50 AM, Timur Iskhodzhanov <timurrrr at google.com> wrote:
> Author: timurrrr
> Date: Wed Mar 26 04:50:36 2014
> New Revision: 204790
>
> URL: http://llvm.org/viewvc/llvm-project?rev=204790&view=rev
> Log:
> Fix PR19239 - Add support for generating debug info for functions without lexical scopes and/or debug info at all

I don't really understand this change from the code involved (perhaps
when I get to the tests it'll make more sense) but what kind of debug
info (since this is in WinCode I assume we're talking about COFF and
we only support line tables there, right?) can you produce for a
function with no debug info? All you have is a function name... which
you'd already have (except inlining?) without emitting any debug
info/line tables.

So is that what this is - the ability to ascribe non-debug-built
functions inlined into other functions by name, even if you don't have
line/file information for the functions or any of their instructions?
(do we keep track of that through inlining? I would've assumed the
debug intrinsics/per-instruction debug info was the only thing that
told us inlined instructions came from another function)

>
> Modified:
>     llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.cpp
>     llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.h
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.cpp?rev=204790&r1=204789&r2=204790&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.cpp Wed Mar 26 04:50:36 2014
> @@ -131,9 +131,12 @@ void WinCodeViewLineTables::emitDebugInf
>    // For each function there is a separate subsection
>    // which holds the PC to file:line table.
>    const MCSymbol *Fn = Asm->getSymbol(GV);
> -  const FunctionInfo &FI = FnDebugInfo[GV];
>    assert(Fn);
> -  assert(FI.Instrs.size() > 0);
> +
> +  const FunctionInfo &FI = FnDebugInfo[GV];
> +  if (FI.Instrs.empty())
> +    return;
> +  assert(FI.End && "Don't know where the function ends?");
>
>    // PCs/Instructions are grouped into segments sharing the same filename.
>    // Pre-calculate the lengths (in instructions) of these segments and store
> @@ -264,12 +267,6 @@ void WinCodeViewLineTables::beginFunctio
>    if (!Asm || !Asm->MMI->hasDebugInfo())
>      return;
>
> -  // 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);
> -  if (LScopes.empty())
> -    return;
> -
>    const Function *GV = MF->getFunction();
>    assert(FnDebugInfo.count(GV) == false);
>    VisitedFunctions.push_back(GV);
> @@ -311,13 +308,12 @@ void WinCodeViewLineTables::endFunction(
>    if (!Asm || !CurFn)  // We haven't created any debug info for this function.
>      return;
>
> -  if (CurFn->Instrs.empty())
> -    llvm_unreachable("Can this ever happen?");
> -
> -  // Define end label for subprogram.
> -  MCSymbol *FunctionEndSym = Asm->OutStreamer.getContext().CreateTempSymbol();
> -  Asm->OutStreamer.EmitLabel(FunctionEndSym);
> -  CurFn->End = FunctionEndSym;
> +  if (!CurFn->Instrs.empty()) {
> +    // Define end label for subprogram.
> +    MCSymbol *FunctionEndSym = Asm->OutStreamer.getContext().CreateTempSymbol();
> +    Asm->OutStreamer.EmitLabel(FunctionEndSym);
> +    CurFn->End = FunctionEndSym;
> +  }
>    CurFn = 0;
>  }
>
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.h?rev=204790&r1=204789&r2=204790&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.h (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/WinCodeViewLineTables.h Wed Mar 26 04:50:36 2014
> @@ -32,13 +32,13 @@ namespace llvm {
>  class WinCodeViewLineTables : public AsmPrinterHandler {
>    AsmPrinter *Asm;
>    DebugLoc PrevInstLoc;
> -  LexicalScopes LScopes;
>
>    // For each function, store a vector of labels to its instructions, as well as
>    // to the end of the function.
>    struct FunctionInfo {
>      SmallVector<MCSymbol *, 10> Instrs;
>      MCSymbol *End;
> +    FunctionInfo() : End(0) {}
>    } *CurFn;
>
>    typedef DenseMap<const Function *, FunctionInfo> FnDebugInfoTy;
>
>
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