[COMMITTED] c++: Fix constexpr vs. omitted aggregate init.
Jason Merrill
jason@redhat.com
Tue Feb 4 22:27:00 GMT 2020
Value-initialization is importantly different from {}-initialization for
this testcase, where the former calls the deleted S constructor and the
latter initializes S happily.
Tested x86_64-pc-linux-gnu, applying to trunk.
PR c++/90951
* constexpr.c (cxx_eval_array_reference): {}-initialize missing
elements instead of value-initializing them.
---
gcc/cp/constexpr.c | 12 ++++++++++--
gcc/testsuite/g++.dg/cpp0x/constexpr-array24.C | 10 ++++++++++
2 files changed, 20 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-array24.C
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index c35ec5acc97..8a02c6e0713 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -3324,8 +3324,16 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t,
}
/* If it's within the array bounds but doesn't have an explicit
- initializer, it's value-initialized. */
- tree val = build_value_init (elem_type, tf_warning_or_error);
+ initializer, it's initialized from {}. But use build_value_init
+ directly for non-aggregates to avoid creating a garbage CONSTRUCTOR. */
+ tree val;
+ if (CP_AGGREGATE_TYPE_P (elem_type))
+ {
+ tree empty_ctor = build_constructor (init_list_type_node, NULL);
+ val = digest_init (elem_type, empty_ctor, tf_warning_or_error);
+ }
+ else
+ val = build_value_init (elem_type, tf_warning_or_error);
return cxx_eval_constant_expression (ctx, val, lval, non_constant_p,
overflow_p);
}
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-array24.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-array24.C
new file mode 100644
index 00000000000..538969830ba
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-array24.C
@@ -0,0 +1,10 @@
+// PR c++/90951
+// { dg-do compile { target c++11 } }
+
+#define assert(expr) static_assert (expr, #expr)
+
+struct S { const char a[2]; };
+
+constexpr struct S a[1][1][1] = { };
+
+assert ('\0' == *a[0][0][0].a);
base-commit: a1c9c9ff06ab15e697d5bac6ea6e5da2df840cf5
--
2.18.1
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