https://gcc.gnu.org/g:899b5be8b9720e381c7ea99ba27a4cbb165c003b
commit r15-4927-g899b5be8b9720e381c7ea99ba27a4cbb165c003b
Author: Piotr Trojanek <troja...@adacore.com>
Date: Tue Oct 15 10:53:47 2024 +0200
ada: Move special case for null string literal from frontend to backend
Previously the lower bound of string literals indexed by non-static
integer types was artificially set to 1 in the frontend. This was to
avoid an overflow in calculation of a null string size by the GCC
backend, which was causing an excessively large binary object file.
However, setting the lower bound to 1 was problematic for GNATprove,
which could not easily retrieve the lower bound of string literals.
This patch avoids the overflow in GCC by recognizing null string literal
subtypes in Gigi.
gcc/ada/ChangeLog:
* gcc-interface/decl.cc (gnat_to_gnu_entity): Recognize null
string literal subtypes and set their bounds to 1 .. 0.
Diff:
---
gcc/ada/gcc-interface/decl.cc | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff --git a/gcc/ada/gcc-interface/decl.cc b/gcc/ada/gcc-interface/decl.cc
index f5188ddc8bca..32e476c69936 100644
--- a/gcc/ada/gcc-interface/decl.cc
+++ b/gcc/ada/gcc-interface/decl.cc
@@ -3110,14 +3110,24 @@ gnat_to_gnu_entity (Entity_Id gnat_entity, tree
gnu_expr, bool definition)
tree gnu_string_index_type
= get_base_type (TREE_TYPE (TYPE_INDEX_TYPE
(TYPE_DOMAIN (gnu_string_array_type))));
+
+ /* For a null string literal we set the bounds to 1 .. 0, to
+ avoid a possible overflow when calculating the upper bound
+ as LOWER_BOUND + LENGTH - 1. */
+ const bool is_null_string
+ = String_Literal_Length (gnat_entity) == Uint_0;
tree gnu_lower_bound
- = convert (gnu_string_index_type,
+ = is_null_string ?
+ build_int_cst (gnu_string_index_type, 1) :
+ convert (gnu_string_index_type,
gnat_to_gnu (String_Literal_Low_Bound (gnat_entity)));
tree gnu_length
= UI_To_gnu (String_Literal_Length (gnat_entity),
gnu_string_index_type);
tree gnu_upper_bound
- = build_binary_op (PLUS_EXPR, gnu_string_index_type,
+ = is_null_string ?
+ build_int_cst (gnu_string_index_type, 0) :
+ build_binary_op (PLUS_EXPR, gnu_string_index_type,
gnu_lower_bound,
int_const_binop (MINUS_EXPR, gnu_length,
convert (gnu_string_index_type,
