llvm dev - Sep 2018 - Obtaining the origin function for a local var after inlining

(I think I've asked a similar question off-list a couple of times, but
never got an answer)

Hi folks,

For [K]MSAN we need to figure out which inlined function a local var
originally belonged to in the source file.
E.g. when a local buffer %buf is declared in @bar(), but @bar() is
inlined into @foo(), then there's a local %buf.i in @foo(), but we
need to determine that the local came from @bar(). In the case of
nested inline functions we need the deepest one.

Is there any existing code for that? If not, which debug info
constructs do we need to look up to get this information?

https://llvm.org/docs/SourceLevelDebugging.html mentions
@llvm.dbg.addr as the source of information about a local var, but the
ToT Clang doesn't emit it. There're calls to @llvm.debug.declare in
the IR, but it's said to be deprecated, so I'm not sure if it's ok
to
use it.

Thanks in advance,
-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

I wanted to start a migration from dbg.declare to dbg.addr, but never
finished it. For your purposes, they are probably equivalent. The slight
semantic difference is that dbg.declare cannot be mixed with dbg.value to
create a variable that is sometimes in memory and sometimes a pure value.

To distinguish between two inlined copies of the same variable, look at the
inlinedAt location of the location of the dbg intrinsic. The inlinedAt
location will be distinct for every inlined call site. You can see how it
is used in CodeGen/AsmPrinter/Dwarf* by looking for uses of InlinedEntity:
  using InlinedEntity = std::pair<const DINode *, const DILocation *>;
...

  for (const auto &VI : Asm->MF->getVariableDbgInfo()) {
    if (!VI.Var)
      continue;
    assert(VI.Var->isValidLocationForIntrinsic(VI.Loc) &&
           "Expected inlined-at fields to agree");

    InlinedEntity Var(VI.Var, VI.Loc->getInlinedAt());
...


On Mon, Sep 17, 2018 at 7:00 AM Alexander Potapenko <glider at google.com>
wrote:
> (I think I've asked a similar question off-list a couple of times, but
> never got an answer)
>
> Hi folks,
>
> For [K]MSAN we need to figure out which inlined function a local var
> originally belonged to in the source file.
> E.g. when a local buffer %buf is declared in @bar(), but @bar() is
> inlined into @foo(), then there's a local %buf.i in @foo(), but we
> need to determine that the local came from @bar(). In the case of
> nested inline functions we need the deepest one.
>
> Is there any existing code for that? If not, which debug info
> constructs do we need to look up to get this information?
>
> https://llvm.org/docs/SourceLevelDebugging.html mentions
> @llvm.dbg.addr as the source of information about a local var, but the
> ToT Clang doesn't emit it. There're calls to @llvm.debug.declare in
> the IR, but it's said to be deprecated, so I'm not sure if it's
ok to
> use it.
>
> Thanks in advance,
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
>
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> On Sep 17, 2018, at 6:59 AM, Alexander Potapenko via llvm-dev <llvm-dev
at lists.llvm.org> wrote:
> 
> (I think I've asked a similar question off-list a couple of times, but
> never got an answer)
> 
> Hi folks,
> 
> For [K]MSAN we need to figure out which inlined function a local var
> originally belonged to in the source file.
If you are looking at a llvm.dbg.declar/value/addr intrinsic, then the
DILocation attached to the intrinsic indirectly points there:

  DIScope *Scope = DILocation(dbg_intrinsic.getDebugLoc()).getScope();
  while (!isa<DISubprogram>(Scope))
    Scope = Scope->getScope();
  auto *origFunction = cast<DIFunction>(Scope);

if you want to find the function that it was inlined *into* then you need to
follow the inlinedAt link in the DILoation.

-- adrian
> E.g. when a local buffer %buf is declared in @bar(), but @bar() is
> inlined into @foo(), then there's a local %buf.i in @foo(), but we
> need to determine that the local came from @bar(). In the case of
> nested inline functions we need the deepest one.
> 
> Is there any existing code for that? If not, which debug info
> constructs do we need to look up to get this information?
> 
> https://llvm.org/docs/SourceLevelDebugging.html mentions
> @llvm.dbg.addr as the source of information about a local var, but the
> ToT Clang doesn't emit it. There're calls to @llvm.debug.declare in
> the IR, but it's said to be deprecated, so I'm not sure if it's
ok to
> use it.
> 
> Thanks in advance,
> -- 
> Alexander Potapenko
> Software Engineer
> 
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
> 
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

On Tue, Sep 18, 2018 at 1:56 AM Adrian Prantl <aprantl at apple.com>
wrote:
>
>
>
> > On Sep 17, 2018, at 6:59 AM, Alexander Potapenko via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> >
> > (I think I've asked a similar question off-list a couple of times,
but
> > never got an answer)
> >
> > Hi folks,
> >
> > For [K]MSAN we need to figure out which inlined function a local var
> > originally belonged to in the source file.
>
> If you are looking at a llvm.dbg.declar/value/addr intrinsic, then the
DILocation attached to the intrinsic indirectly points there:
>
>   DIScope *Scope = DILocation(dbg_intrinsic.getDebugLoc()).getScope();
>   while (!isa<DISubprogram>(Scope))
>     Scope = Scope->getScope();
>   auto *origFunction = cast<DIFunction>(Scope);
This works, thank you!

(I had to slightly modify the code FWIW:
    DILocation *DIL = dbg_intrinsic.getDebugLoc();
    if (DIL) {
      DIScope *Scope = DIL->getScope();
      while (Scope && !isa<DISubprogram>(Scope))
        Scope = Scope->getScope().resolve();
      auto *origFunction = cast<DISubprogram>(Scope)
)

I also thought that it would be natural if the AllocaInst
corresponding to the llvm.dbg.declare() call will share the same
DILocation as the debug intrinsic.
Does anyone have an idea why this isn't so?
Right now one needs to build a mapping between AllocaInst and
llvm.dbg.declare() in order to get the debug info for the allocation.
> if you want to find the function that it was inlined *into* then you need
to follow the inlinedAt link in the DILoation.
>
> -- adrian
>
> > E.g. when a local buffer %buf is declared in @bar(), but @bar() is
> > inlined into @foo(), then there's a local %buf.i in @foo(), but we
> > need to determine that the local came from @bar(). In the case of
> > nested inline functions we need the deepest one.
> >
> > Is there any existing code for that? If not, which debug info
> > constructs do we need to look up to get this information?
> >
> > https://llvm.org/docs/SourceLevelDebugging.html mentions
> > @llvm.dbg.addr as the source of information about a local var, but the
> > ToT Clang doesn't emit it. There're calls to
@llvm.debug.declare in
> > the IR, but it's said to be deprecated, so I'm not sure if
it's ok to
> > use it.
> >
> > Thanks in advance,
> > --
> > Alexander Potapenko
> > Software Engineer
> >
> > Google Germany GmbH
> > Erika-Mann-Straße, 33
> > 80636 München
> >
> > Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> > Registergericht und -nummer: Hamburg, HRB 86891
> > Sitz der Gesellschaft: Hamburg
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg