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c++: Tweak reshape_init_array_1 [PR94124]

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Isn't it wasteful to first copy perhaps a large constructor (recursively)
and then truncate it to very few elts (zero in this case)?

> 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.

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.

2020-03-12  Jakub Jelinek  <jakub@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.
This commit is contained in:
Jakub Jelinek 2020-03-12 08:28:05 +01:00
parent aedb4c8fc7
commit 4069adf4bb
2 changed files with 23 additions and 5 deletions
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9
gcc/cp/ChangeLog
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@ -1,3 +1,10 @@
2020-03-12 Jakub Jelinek <jakub@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.
2020-03-11 Jason Merrill <jason@redhat.com>
PR c++/93907
@ -27,7 +34,7 @@
2020-03-10 Jason Merrill <jason@redhat.com>
PR c++/93956
PR c++/93596
* pt.c (maybe_aggr_guide): Check BRACE_ENCLOSED_INITIALIZER_P.
2020-03-10 Jason Merrill <jason@redhat.com>

19
gcc/cp/decl.c
View file

@ -6066,10 +6066,21 @@ reshape_init_array_1 (tree elt_type, tree max_index, reshape_iter *d,
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;
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;