On 7/21/23 18:38, Marek Polacek wrote:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk/13?
-- >8 --
This code in cxx_eval_array_reference has been hard to get right.
In r12-2304 I added some code; in r13-5693 I removed some of it.
Here the problematic line is "S s = arr[0];" which causes a crash
on the assert in verify_ctor_sanity:
gcc_assert (!ctx->object || !DECL_P (ctx->object)
|| ctx->global->get_value (ctx->object) == ctx->ctor);
ctx->object is the VAR_DECL 's', which is correct here. The second
line points to the problem: we replaced ctx->ctor in
cxx_eval_array_reference:
new_ctx.ctor = build_constructor (elem_type, NULL); // #1
...and this code doesn't also clear(/set) new_ctx.object like everywhere
else in constexpr.cc that sets new_ctx.ctor. Fixing that should make
the testcase work.
which I think we shouldn't have; the CONSTRUCTOR we created in
cxx_eval_constant_expression/DECL_EXPR
new_ctx.ctor = build_constructor (TREE_TYPE (r), NULL);
had the right type.
Indeed, and using it rather than building a new one seems like a valid
optimization for trunk.
I also notice that the DECL_EXPR code calls unshare_constructor, which
should be unnecessary if init == ctx->ctor?
We still need #1 though. E.g., in constexpr-96241.C, we never
set ctx.ctor/object before calling cxx_eval_array_reference, so
we have to build a CONSTRUCTOR there. And in constexpr-101371-2.C
we have a ctx.ctor, but it has the wrong type, so we need a new one.
PR c++/110382
gcc/cp/ChangeLog:
* constexpr.cc (cxx_eval_array_reference): Create a new constructor
only when we don't already have a matching one.
gcc/testsuite/ChangeLog:
* g++.dg/cpp1y/constexpr-110382.C: New test.
---
gcc/cp/constexpr.cc | 5 ++++-
gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C | 17 +++++++++++++++++
2 files changed, 21 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C
diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc
index fb94f3cefcb..518b7c7a2d5 100644
--- a/gcc/cp/constexpr.cc
+++ b/gcc/cp/constexpr.cc
@@ -4291,7 +4291,10 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree
t,
else
val = build_value_init (elem_type, tf_warning_or_error);
- if (!SCALAR_TYPE_P (elem_type))
+ if (!SCALAR_TYPE_P (elem_type)
+ /* Create a new constructor only if we don't already have one that
+ is suitable. */
+ && !(ctx->ctor && same_type_p (elem_type, TREE_TYPE (ctx->ctor))))
We generally use same_type_ignoring_top_level_qualifiers_p in the
constexpr code.
Jason
