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c++: Tweak VLA representation. 

If we put the SAVE_EXPR for a VLA size inside the MINUS_EXPR rather than
outside, it will work better with constant folding.

The equivalent change was made in the C front-end in 2004, in commit
r0-64535-g8b0b9aefd29dfe6398857bcf5628662e2f0e21f6

gcc/cp/ChangeLog
2020-05-11  Jason Merrill  <jason@redhat.com>

	* decl.c (compute_array_index_type_loc): Stabilize before building
	the MINUS_EXPR.
This commit is contained in:
Jason Merrill 2020-05-11 14:05:46 -04:00
parent 3a3e1ea9c6
commit f315d1477d
2 changed files with 14 additions and 5 deletions
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5
gcc/cp/ChangeLog
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@ -1,3 +1,8 @@
2020-05-11 Jason Merrill <jason@redhat.com>
* decl.c (compute_array_index_type_loc): Stabilize before building
the MINUS_EXPR.
2020-05-11 Jason Merrill <jason@redhat.com>
* decl.c (grokdeclarator): Adjust deprecated_state here.

14
gcc/cp/decl.c
View File

@ -10449,6 +10449,15 @@ compute_array_index_type_loc (location_t name_loc, tree name, tree size,
itype = build_min (MINUS_EXPR, sizetype, size, integer_one_node);
else
{
if (!TREE_CONSTANT (size))
{
/* A variable sized array. Arrange for the SAVE_EXPR on the inside
of the MINUS_EXPR, which allows the -1 to get folded with the +1
that happens when building TYPE_SIZE. */
size = variable_size (size);
stabilize_vla_size (size);
}
/* Compute the index of the largest element in the array. It is
one less than the number of elements in the array. We save
and restore PROCESSING_TEMPLATE_DECL so that computations in
@ -10466,11 +10475,6 @@ compute_array_index_type_loc (location_t name_loc, tree name, tree size,
if (!TREE_CONSTANT (itype))
{
/* A variable sized array. */
itype = variable_size (itype);
stabilize_vla_size (itype);
if (sanitize_flags_p (SANITIZE_VLA)
&& current_function_decl != NULL_TREE)
{