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PR c++/86320 - memory-hog with std::array of pair

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* typeck2.c (process_init_constructor_array): Only compute a
	constant initializer once.

In this PR, we have a large std::array of pairs.  Since the C array is
wrapped in a class we don't go to build_vec_init, so we end up with
digest_init wanting to build up the element initializer for each element of
the array.

In the more general case, like 80272, we have a data structure problem: we
don't currently have a good way of expressing the same dynamic
initialization of many elements within a CONSTRUCTOR.  RANGE_EXPR probably
ought to work, but will need more work at genericize or gimplify time.

But in this case, the initialization for each element reduces to constant
0, so we don't even need to add anything to the CONSTRUCTOR.  We just need
to realize that if the initializer for one element is 0, the others will be
as well, and we don't need to iterate over the whole array.

For the trunk, I also use a RANGE_EXPR to handle constant initialization by
a value other than 0.

void foo ()
{
  std::array<std::pair<int, int>, 1024 * 1024> arr {};
}

From-SVN: r262173
This commit is contained in:
Jason Merrill 2018-06-26 22:59:44 -04:00 • committed by Jason Merrill
parent 6147a53a9c
commit 307193b82c
2 changed files with 19 additions and 1 deletions
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4
gcc/cp/ChangeLog
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@ -1,5 +1,9 @@
2018-06-26 Jason Merrill <jason@redhat.com>
PR c++/86320 - memory-hog with std::array of pair
* typeck2.c (process_init_constructor_array): Only compute a
constant initializer once.
PR c++/80290 - memory-hog with std::pair.
* pt.c (fn_type_unification): Add convs parameter.
(check_non_deducible_conversion): Remember conversion.

16
gcc/cp/typeck2.c
View file

@ -1365,8 +1365,22 @@ process_init_constructor_array (tree type, tree init, int nested,
if (next)
{
flags |= picflag_from_initializer (next);
CONSTRUCTOR_APPEND_ELT (v, size_int (i), next);
if (len > i+1
&& (initializer_constant_valid_p (next, TREE_TYPE (next))
== null_pointer_node))
{
tree range = build2 (RANGE_EXPR, size_type_node,
build_int_cst (size_type_node, i),
build_int_cst (size_type_node, len - 1));
CONSTRUCTOR_APPEND_ELT (v, range, next);
break;
}
else
CONSTRUCTOR_APPEND_ELT (v, size_int (i), next);
}
else
/* Don't bother checking all the other elements. */
break;
}
CONSTRUCTOR_ELTS (init) = v;