lto gimple types and debug info

[Alexandre Oliva]

On Jul 27, 2008, Mark Mitchell <mark@codesourcery.com> wrote:

> In that case, I'm not sure that *type* ought to be modified at all,
> from the debug perspective.  To the extent there's still an object of
> type "struct X" around, it's type is still what it was.  And other
> things you might do in a debugger, like ask "What member functions
> does class X have?", have the same answer no matter the layout chosen
> by the compiler, including throwing out half the fields and leaving
> the rest in random registers.  For that matter, "print sizeof(X)"
> should print the same value when debugging optimized code as when
> debugging unoptimized code, even if the compiler has optimized X away
> to an empty structure!

+1

> There are other things we could do, like mark the *variables* of type
> X (rather than the type) as having no location, so that you can't
> print/modify objects that have been optimized in this way.

Or construct the location lists using DW_OP_piece et al to denote the
location of each fragment of the object.

> I'm curious what we do with SRA at the moment.  This is the same
> sort of problem; do we have any solutions at present?

no, we don't do this with SRA, but I designed VTA so that it would be
trivial to annotate the scalarization assignments, which would then be
maintained all the way up to var-tracking, where it could be turned
into debug info for the separate pieces.

-- 
Alexandre Oliva         http://www.lsd.ic.unicamp.br/~oliva/
Free Software Evangelist  oliva@{lsd.ic.unicamp.br, gnu.org}
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Red Hat Compiler Engineer   aoliva@{redhat.com, gcc.gnu.org}