[PATCH] D18565: Implement an "I'm dtrace, please retain all debug types" option.

[Adrian Prantl via cfe-commits]

> On Mar 29, 2016, at 10:06 PM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> 
> On Tue, Mar 29, 2016 at 12:03 PM, Adrian Prantl via cfe-commits <cfe-commits at lists.llvm.org <mailto:cfe-commits at lists.llvm.org>> wrote:
> 
> > On Mar 29, 2016, at 12:00 PM, Joerg Sonnenberger <joerg at britannica.bec.de <mailto:joerg at britannica.bec.de>> wrote:
> >
> > On Tue, Mar 29, 2016 at 06:47:24PM +0000, Adrian Prantl via cfe-commits wrote:
> >> This code in this patch listens to the driver option -gfull, and lowers it to the new cc1 option -debug-retain-types (1).
> >> When -debug-retain-types is present, CGDebugInfo will retain every(2) type it creates.
> >
> > Is there a good reason for calling it -gfull? I would find something
> > -gall-types or -gretain-all-types to make a lot more sense. This should
> > be orthogonal to other options like providing only line tables?
> 
> My thinking was this:
> The driver already supports -gfull, but it doesn’t do anything.
> This patch can be considered a first step towards making -gfull behave as expected.
> Eventually it should emit debug info for *all* types.
> 
> Seems somewhat problematic to half implement it, though. (admittedly we're just silently ignoring it right now)

I don’t think this is problematic at all. This is incremental development.

> 
> & is 'real' -gfull what dtrace really wants? (seems it isn't - since clang's never really implemented it?)

Admitted, ‘real' -gfull is probably more than it absolutely needs.

> Emitting all types referenced by used (even if later optimized away) code seems like the thing? -greferenced? or maybe a -f flag? Not sure.

I don’t see a compelling case for adding another driver option to the already confusing zoo of existing driver options. Note that we currently also accept a -gused option which according to the driver code is supposed to be the opposite of -gfull. Adding a -greferenced option IMO will only make this more confusion instead of helping.
My suggestion is to have -gfull (also) activate -debug-retain-types. In the somewhat hypothetical scenario that someone implements a more comprehensive version of -gfull we should revisit this and analyze whether the resulting debug information is really too large to be practical, and if we conclude that this is a problem, we can still decide to expose -debug-retain-types to the driver with a new separate option.

-- adrian

>  
> 
> > Joerg
> >
> > PS: Slightly related side question, do we have any tools for extracting
> > a given list of types for retaining? Either by name or global variable
> > expression.
> 
> Extract them from where? Can you give an example?
> 
> -- adrian
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