[cfe-dev] GCOV and stripping debug info

[David Blaikie via cfe-dev]

On Wed, Jan 10, 2018 at 11:48 AM Adrian Prantl <aprantl at apple.com> wrote:

>
>
> > On Jan 10, 2018, at 11:40 AM, David Blaikie <dblaikie at gmail.com> wrote:
> >
> > Implementing GCOV in the new pass manager  (r322126) I'm wondering
> whether the addition of a "StripSymbols(OnlyDebugInfo = true)" pass is
> needed - and maybe that functionality in general can be removed?
> >
> > It was added, I believe, before we had the "NoDebug" style debug info,
> used specifically for profiling, optimization remarks, etc. So when this
> was implemented, stripping the debug info was probably necessary to avoid
> actually emitting debug info into the resulting object files.
> >
> > This could be useful in an LTO like build, if you know the debug info is
> not needed at the LTO stage - strip it out at the end of the frontend
> compile to reduce the size of bitcode files.
>
> You mean that for LTO scheduling an explicit StripSymbols pass is an
> advantage over just using the NoDebug, which only causes the baclkend to
> ignore it? But the debug info will probably be needed for optimization
> remarks during LTO time, wouldn't it?
>

Right - though you could be doing a build that doesn't have remarks
enabled, but wanted debug info locations for something that's
frontend-only? I don't know the full diversity of uses of NoDebug debug
info, but could imagine there might be uses (not sure if there are current
uses - could be future uses, but that's nothing to worry much about/design
for of course) that only need it for the frontend compile.


>
> >
> > So... does this seem relevant here? In general? (I haven't looked at
> what other uses)
>
> As one datapoint, I didn't know we had StripSymbols(OnlyDebugInfo = true)
> as a pass (I only knew about the llvm::stripDebugInfo() functions).
> Grepping for other uses of StripSymbols and stripDebugInfo might be a good
> start.
>

*nod*


>
> -- adrian
> >
> > Totally happy to port the StripSymbols pass to the new pass manager if
> it seems like it's useful/necessary.
> >
> > - Dave
>
>
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