[PATCH] Use vec::reserve before vec_safe_grow_cleared is called

[Richard Biener]

On Sat, Jul 25, 2020 at 2:23 PM Martin Liška <mliska@suse.cz> wrote:
>
> Hello.
>
> When inserting into fast_call_summary (or fast_function_summary), we grow
> a vector to a _exact_ size based on cgraph_max_summary_id or edges_max_summary_id.
> Problem is that it causes very many reallocation and we should rather use ::reserve
> function that selects a reasonable size of a new vector.
>
> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
> Fixes chromium WPA build time:
> https://gist.githubusercontent.com/marxin/223890df4d8d8e490b6b2918b77dacad/raw/f766f6546739e739a273639dde90ac6179aa3077/chromium-gcc10-fixed-summary-crash.svg
>
> Ready to be installed?

OK.  I guess the previous code tried to use less memory.

Thanks,
Richard.

> Thanks,
> Martin
>
> gcc/ChangeLog:
>
>         * symbol-summary.h: Call vec_safe_reserve before grow is called
>         in order to grow to a reasonable size.
>         * vec.h (vec_safe_reserve): Add missing function for vl_ptr
>         type.
> ---
>   gcc/symbol-summary.h | 13 ++++++++++---
>   gcc/vec.h            | 11 +++++++++++
>   2 files changed, 21 insertions(+), 3 deletions(-)
>
> diff --git a/gcc/symbol-summary.h b/gcc/symbol-summary.h
> index a38eb1db778..fa1df5c8015 100644
> --- a/gcc/symbol-summary.h
> +++ b/gcc/symbol-summary.h
> @@ -354,8 +354,11 @@ public:
>         id = this->m_symtab->assign_summary_id (node);
>
>       if ((unsigned int)id >= m_vector->length ())
> -      vec_safe_grow_cleared (m_vector,
> -                            this->m_symtab->cgraph_max_summary_id);
> +      {
> +       int newlen = this->m_symtab->cgraph_max_summary_id;
> +       vec_safe_reserve (m_vector, newlen - m_vector->length ());
> +       m_vector->quick_grow_cleared (newlen);
> +      }
>
>       if ((*m_vector)[id] == NULL)
>         (*m_vector)[id] = this->allocate_new ();
> @@ -812,7 +815,11 @@ public:
>         id = this->m_symtab->assign_summary_id (edge);
>
>       if ((unsigned)id >= m_vector->length ())
> -      vec_safe_grow_cleared (m_vector, this->m_symtab->edges_max_summary_id);
> +      {
> +       int newlen = this->m_symtab->edges_max_summary_id;
> +       m_vector->reserve (newlen - m_vector->length ());
> +       m_vector->quick_grow_cleared (newlen);
> +      }
>
>       if ((*m_vector)[id] == NULL)
>         (*m_vector)[id] = this->allocate_new ();
> diff --git a/gcc/vec.h b/gcc/vec.h
> index bd7c7351dcd..3ad99b83690 100644
> --- a/gcc/vec.h
> +++ b/gcc/vec.h
> @@ -753,6 +753,17 @@ vec_safe_grow_cleared (vec<T, va_heap, vl_ptr> *&v,
>     v->safe_grow_cleared (len PASS_MEM_STAT);
>   }
>
> +/* If V does not have space for NELEMS elements, call
> +   V->reserve(NELEMS, EXACT).  */
> +
> +template<typename T>
> +inline bool
> +vec_safe_reserve (vec<T, va_heap, vl_ptr> *&v, unsigned nelems, bool exact = false
> +                 CXX_MEM_STAT_INFO)
> +{
> +  return v->reserve (nelems, exact);
> +}
> +
>
>   /* If V is NULL return false, otherwise return V->iterate(IX, PTR).  */
>   template<typename T, typename A>
> --
> 2.27.0
>