[gcc r12-5325] c-family: don't cache large vecs

[gcc r12-5325] c-family: don't cache large vecs

[Jason Merrill]

https://gcc.gnu.org/g:395848255cfa88f6f0f33a9b14c79e584a05d6fc

commit r12-5325-g395848255cfa88f6f0f33a9b14c79e584a05d6fc
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Nov 10 16:23:12 2021 -0500

    c-family: don't cache large vecs
    
    Patrick observed recently that an element of the vector cache could be
    arbitrarily large.  Let's only cache relatively small vecs.
    
    gcc/c-family/ChangeLog:
    
            * c-common.c (release_tree_vector): Only cache vecs smaller than
            16 elements.

Diff:
---
 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);
+	}
     }
 }