Compiling c++ template is very slow.

[Nathan Sidwell]

On 03/09/2018 06:51 AM, Richard Biener wrote:
> On Fri, Mar 9, 2018 at 11:32 AM, Richard Biener
> <richard.guenther@gmail.com> wrote:

> callgrind shows that propagate_binfo_offsets recursing
> to self very many times is likely the issue.  Your templates
> build a very deep inheritance chain and it seems that
> the binfo offset propagation ends up being exponential here.
> 
> I would have expected that any bases have already correct
> offsets so we don't need the recursion to bases of bases?
> 
> Ah, so in this case we have offset of 1 because sizeof is
> always nonzero.  So the issue might just be that
> BINFO_OFFSET is not relative to the parent?

Correct, it's relative to the complete object.

> doens't improve things.  We call this functions millions of times
> creating millions of INTEGER_CSTs.  Can BINFO_OFFSET be
> non-constant?

No. (if it's a vbase, it shows the offset in the complete object, IIRC, 
and there's other data to let code generation know some vtable 
inspection is needed when the dynamic type is unknown).

nathan

-- 
Nathan Sidwell