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[2603:7000:9500:34a5::1db4]) by smtp.gmail.com with ESMTPSA id r5-20020a0ce285000000b0062de51d8a12sm3853427qvl.26.2023.07.24.15.37.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Jul 2023 15:37:57 -0700 (PDT) Date: Mon, 24 Jul 2023 18:37:55 -0400 From: Marek Polacek To: Jason Merrill Cc: GCC Patches , Patrick Palka Subject: [PATCH v2] c++: fix ICE with constexpr ARRAY_REF [PR110382] Message-ID: References: <20230721223835.630543-1-polacek@redhat.com> <77708a9e-b677-e655-a3cc-a9af6d0b1321@redhat.com> MIME-Version: 1.0 In-Reply-To: <77708a9e-b677-e655-a3cc-a9af6d0b1321@redhat.com> User-Agent: Mutt/2.2.9 (2022-11-12) X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-12.5 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE,SPF_NONE,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Sat, Jul 22, 2023 at 12:28:59AM -0400, Jason Merrill wrote: > 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. Right, but then we'd be back pre-r12-2304 or r13-5693... ...except it should work to always clear the object, like below. > > 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. Agreed, I kept it. > I also notice that the DECL_EXPR code calls unshare_constructor, which > should be unnecessary if init == ctx->ctor? It looks like init == ctx->ctor only happens only with this new testcase. I'm not sure it's worth it adding code for such a rare case? > > 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. True, changed. Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? For 13, I guess I should only clear the object and leave out the same_type_ bit. -- >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 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. 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. We can fix the problem by always clearing the object, and, as an optimization, only create/free a new ctor when actually needed. 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. Clear the object when the type is non-scalar. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/constexpr-110382.C: New test. --- gcc/cp/constexpr.cc | 17 +++++++++++++++-- gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C | 17 +++++++++++++++++ 2 files changed, 32 insertions(+), 2 deletions(-) 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..054812bcb72 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -4291,15 +4291,28 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t, else val = build_value_init (elem_type, tf_warning_or_error); + bool new_ctor; if (!SCALAR_TYPE_P (elem_type)) { new_ctx = *ctx; - new_ctx.ctor = build_constructor (elem_type, NULL); + /* We clear the object here. We used to replace it with T, but that + caused problems (101371, 108158); and anyway, T is the initializer, + not the target object. */ + new_ctx.object = NULL_TREE; + /* Create a new constructor only if we don't already have a suitable + one. */ + new_ctor = (!ctx->ctor + || !same_type_ignoring_top_level_qualifiers_p + (elem_type, TREE_TYPE (ctx->ctor))); + if (new_ctor) + new_ctx.ctor = build_constructor (elem_type, NULL); ctx = &new_ctx; } + else + new_ctor = false; t = cxx_eval_constant_expression (ctx, val, lval, non_constant_p, overflow_p); - if (!SCALAR_TYPE_P (elem_type) && t != ctx->ctor) + if (new_ctor && t != ctx->ctor) free_constructor (ctx->ctor); return t; } diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C new file mode 100644 index 00000000000..317c5ecfcd5 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-110382.C @@ -0,0 +1,17 @@ +// PR c++/110382 +// { dg-do compile { target c++14 } } + +struct S { + double a = 0; +}; + +constexpr double +g () +{ + S arr[1]; + S s = arr[0]; + (void) arr[0]; + return s.a; +} + +int main() { return g (); } base-commit: 96482ffe60d9bdec802fcad705c69641b2a3e040 -- 2.41.0