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
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog
2020-05-11 Jason Merrill <ja...@redhat.com>
* decl.c (compute_array_index_type_loc): Stabilize before building
the MINUS_EXPR.
---
gcc/cp/decl.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index adf94658420..dea1ba07c0e 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -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)
{
base-commit: 2b2d298ff845ab7a07ffbd51da79473736da3324
--
2.18.1
