On Tue, Nov 16, 2021 at 11:53:14AM -0500, Jason Merrill via Gcc-patches wrote:
> Patrick observed recently that an element of the vector cache could be
> arbitrarily large. Let's only cache relatively small vecs.
>
> This has no effect on compiling the libstdc++ stdc++.h, presumably because
> nothing in the library requires a vec that large. I figure that this makes it
> more likely that a subsequent long list will reuse the same memory when the
> later vec gets expanded.
>
> Does this make sense to others?
Looks good to me.
> gcc/c-family/ChangeLog:
>
> * c-common.c (release_tree_vector): Only cache vecs smaller than
> 16 elements.
> ---
> gcc/c-family/c-common.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
> index 436df45df68..90e8ec87b6b 100644
> --- a/gcc/c-family/c-common.c
> +++ b/gcc/c-family/c-common.c
> @@ -8213,8 +8213,16 @@ release_tree_vector (vec<tree, va_gc> *vec)
> {
> if (vec != NULL)
> {
> - vec->truncate (0);
> - vec_safe_push (tree_vector_cache, vec);
> + if (vec->allocated () >= 16)
> + /* Don't cache vecs that have expanded more than once. On a p64
> + target, vecs double in alloc size with each power of 2 elements, e.g
> + at 16 elements the alloc increases from 128 to 256 bytes. */
> + vec_free (vec);
> + else
> + {
> + vec->truncate (0);
> + vec_safe_push (tree_vector_cache, vec);
> + }
> }
> }
>
>
> base-commit: 132f1c27770fa6dafdf14591878d301aedd5ae16
> --
> 2.27.0
>
Marek
