From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 1DA083858D1E for ; Tue, 31 Jan 2023 02:36:05 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 1DA083858D1E Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1675132564; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=NtB+HGaxVjRfIPD7hbzsvVr8Yw9VREJRdHUxzNI0ETE=; b=TqDdWJ2uo0CAdwfQ3MBq4ngcRuhY3RSAPQgqJLK11V2eEzE4aghU5Jngj+UOM9kzLDBemJ GXO6ken1UFGL3l7b8Arj6+Mpp0AhtR6rng3399VpNH78C+JMOAUEWZeYgT/0ehUk92k3uJ 0w0e00qwJDuL8V3I1I3RSfwvKZDkams= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-615-9Ji3Wr7ZMQGoSf9PAcIlWw-1; Mon, 30 Jan 2023 21:35:54 -0500 X-MC-Unique: 9Ji3Wr7ZMQGoSf9PAcIlWw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 276EE3C10141 for ; Tue, 31 Jan 2023 02:35:54 +0000 (UTC) Received: from pdp-11.lan (unknown [10.22.8.110]) by smtp.corp.redhat.com (Postfix) with ESMTP id 049361121314; Tue, 31 Jan 2023 02:35:53 +0000 (UTC) From: Marek Polacek To: GCC Patches , Jason Merrill Subject: [PATCH] c++: wrong error with constexpr array and value-init [PR108158] Date: Mon, 30 Jan 2023 21:35:49 -0500 Message-Id: <20230131023549.454983-1-polacek@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII"; x-default=true X-Spam-Status: No, score=-12.3 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_H2,SPF_HELO_NONE,SPF_NONE,TXREP 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: In this test case, we find ourselves evaluating 't' which is ((const struct carray *) this)->data_[VIEW_CONVERT_EXPR(index)] in cxx_eval_array_reference. ctx->object is non-null, a RESULT_DECL, so we replace it with 't': new_ctx.object = t; // result_decl replaced and then we go to cxx_eval_constant_expression to evaluate an AGGR_INIT_EXPR, where we end up evaluating an INIT_EXPR (which is in the body of the constructor for seed_or_index): ((struct seed_or_index *) this)->value_ = NON_LVALUE_EXPR <0> whereupon in cxx_eval_store_expression we go to the probe loop where the 'this' is evaluated to ze_set.tables_.first_table_.data_[0] so the 'object' is ze_set, but that isn't in ctx->global->get_value_ptr so we fail with a bogus error. ze_set is not there because it comes from a different constexpr context (it's not in cv_cache either). The problem started with r12-2304 where I added the new_ctx.object replacement. That was to prevent a type mismatch: the type of 't' and ctx.object were different. It seems clear that we shouldn't have replaced ctx.object here. The cxx_eval_array_reference I mentioned earlier is called from cxx_eval_store_expression: 6257 init = cxx_eval_constant_expression (&new_ctx, init, vc_prvalue, 6258 non_constant_p, overflow_p); which already created a new context, whose .object we should be using unless, for instance, INIT contained a.b and we're evaluating the 'a' part, which I think was the case for r12-2304; in that case ctx.object has to be something different. A relatively safe fix should be to check the types before replacing ctx.object, as in the below. Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? PR c++/108158 gcc/cp/ChangeLog: * constexpr.cc (cxx_eval_array_reference): Don't replace new_ctx.object if its type is the same as elem_type. gcc/testsuite/ChangeLog: * g++.dg/cpp1y/constexpr-108158.C: New test. --- gcc/cp/constexpr.cc | 8 +++-- gcc/testsuite/g++.dg/cpp1y/constexpr-108158.C | 32 +++++++++++++++++++ 2 files changed, 38 insertions(+), 2 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp1y/constexpr-108158.C diff --git a/gcc/cp/constexpr.cc b/gcc/cp/constexpr.cc index be99bec17e7..00582cfffe2 100644 --- a/gcc/cp/constexpr.cc +++ b/gcc/cp/constexpr.cc @@ -4301,9 +4301,13 @@ cxx_eval_array_reference (const constexpr_ctx *ctx, tree t, if (!SCALAR_TYPE_P (elem_type)) { new_ctx = *ctx; - if (ctx->object) + if (ctx->object + && !same_type_ignoring_top_level_qualifiers_p + (elem_type, TREE_TYPE (ctx->object))) /* If there was no object, don't add one: it could confuse us - into thinking we're modifying a const object. */ + into thinking we're modifying a const object. Similarly, if + the types are the same, replacing .object could lead to a + failure to evaluate it (c++/108158). */ new_ctx.object = t; new_ctx.ctor = build_constructor (elem_type, NULL); ctx = &new_ctx; diff --git a/gcc/testsuite/g++.dg/cpp1y/constexpr-108158.C b/gcc/testsuite/g++.dg/cpp1y/constexpr-108158.C new file mode 100644 index 00000000000..e5f5e9954e5 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1y/constexpr-108158.C @@ -0,0 +1,32 @@ +// PR c++/108158 +// { dg-do compile { target c++14 } } + +template struct carray { + T data_[N]{}; + constexpr T operator[](long index) const { return data_[index]; } +}; +struct seed_or_index { +private: + long value_ = 0; +}; +template struct pmh_tables { + carray first_table_; + template + constexpr void lookup(KeyType, HasherType) const { + first_table_[0]; + } +}; +template struct unordered_set { + int equal_; + carray keys_; + pmh_tables tables_; + constexpr unordered_set() : equal_{} {} + template + constexpr auto lookup(KeyType key, Hasher hash) const { + tables_.lookup(key, hash); + return keys_; + } +}; +constexpr unordered_set<3> ze_set; +constexpr auto nocount = ze_set.lookup(4, int()); +constexpr auto nocount2 = unordered_set<3>{}.lookup(4, int()); base-commit: 897a0502056e6cc6613f26e0b22d1c1e06b1490f -- 2.39.1