On Wed, Mar 11, 2020 at 04:02:51PM -0400, Jason Merrill via Gcc-patches wrote:
> We should certainly avoid copying if they're the same. The code above for
> only copying the bits that aren't going to be thrown away seems pretty
> straightforward, might as well use it even if the savings aren't likely to
> be large.
So like this if it passes bootstrap/regtest?
Calling vec_safe_truncate with the same number of elts the vector already
has is a nop, so IMHO we just should make sure we only unshare if it
changed.
2020-03-11 Jakub Jelinek <ja...@redhat.com>
PR c++/94124
* decl.c (reshape_init_array_1): Don't unshare constructor if there
aren't any trailing zero elts, otherwise only unshare the first
nelts.
--- gcc/cp/decl.c.jj 2020-03-11 09:28:53.966213943 +0100
+++ gcc/cp/decl.c 2020-03-11 23:19:08.832780798 +0100
@@ -6066,10 +6066,22 @@ reshape_init_array_1 (tree elt_type, tre
overload resolution. E.g., initializing a class from
{{0}} might be invalid while initializing the same class
from {{}} might be valid. */
- if (reuse)
- new_init = unshare_constructor (new_init);
-
- vec_safe_truncate (CONSTRUCTOR_ELTS (new_init), nelts);
+ if (reuse && nelts < CONSTRUCTOR_NELTS (new_init))
+ {
+ vec<constructor_elt, va_gc> *v = NULL;
+ if (nelts)
+ vec_alloc (v, nelts);
+ for (unsigned int i = 0; i < nelts; i++)
+ {
+ constructor_elt elt = *CONSTRUCTOR_ELT (new_init, i);
+ if (TREE_CODE (elt.value) == CONSTRUCTOR)
+ elt.value = unshare_constructor (elt.value);
+ v->quick_push (elt);
+ }
+ new_init = build_constructor (TREE_TYPE (new_init), v);
+ }
+ else
+ vec_safe_truncate (CONSTRUCTOR_ELTS (new_init), nelts);
}
return new_init;
Jakub
