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[69.118.112.187]) by smtp.gmail.com with ESMTPSA id h2-20020a0cb4c2000000b006577e289d35sm1190909qvf.58.2023.09.18.09.12.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 18 Sep 2023 09:12:07 -0700 (PDT) From: Patrick Palka To: gcc-patches@gcc.gnu.org Cc: jason@redhat.com, Patrick Palka Subject: [PATCH v2 2/2] c++: convert_to_void and volatile references Date: Mon, 18 Sep 2023 12:12:02 -0400 Message-ID: <20230918161202.2884010-2-ppalka@redhat.com> X-Mailer: git-send-email 2.42.0.216.gbda494f404 In-Reply-To: <20230918161202.2884010-1-ppalka@redhat.com> References: <20230918161202.2884010-1-ppalka@redhat.com> MIME-Version: 1.0 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=-13.6 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_H3,RCVD_IN_MSPIKE_WL,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: Jason pointed out that even implicit loads of volatile references need to undergo lvalue-to-rvalue conversion, but we currently emit a warning in this case and discard the load. This patch changes this behavior so that we don't issue a warning, and preserve the load. gcc/cp/ChangeLog: * cvt.cc (convert_to_void) : Remove warning for an implicit load of a volatile reference. Simplify as if is_reference is false. Check REFERENCE_REF_P in the test guarding the -Wunused-value diagnostic. gcc/testsuite/ChangeLog: * g++.dg/expr/discarded1a.C: No longer expect warning for implicit load of a volatile reference. * g++.old-deja/g++.bugs/900428_01.C: Likewise. * g++.dg/expr/volatile2.C: New test. --- gcc/cp/cvt.cc | 56 ++----------------- gcc/testsuite/g++.dg/expr/discarded1a.C | 1 - gcc/testsuite/g++.dg/expr/volatile2.C | 12 ++++ .../g++.old-deja/g++.bugs/900428_01.C | 26 ++++----- 4 files changed, 30 insertions(+), 65 deletions(-) create mode 100644 gcc/testsuite/g++.dg/expr/volatile2.C diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc index 4424670356c..1cb6c1222c2 100644 --- a/gcc/cp/cvt.cc +++ b/gcc/cp/cvt.cc @@ -1251,12 +1251,9 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain) { tree type = TREE_TYPE (expr); int is_volatile = TYPE_VOLATILE (type); - if (is_volatile) - complete_type (type); - int is_complete = COMPLETE_TYPE_P (type); /* Can't load the value if we don't know the type. */ - if (is_volatile && !is_complete) + if (is_volatile && !COMPLETE_TYPE_P (complete_type (type))) { if (complain & tf_warning) switch (implicit) @@ -1298,50 +1295,7 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain) gcc_unreachable (); } } - /* Don't load the value if this is an implicit dereference, or if - the type needs to be handled by ctors/dtors. */ - else if (is_volatile && is_reference) - { - if (complain & tf_warning) - switch (implicit) - { - case ICV_CAST: - warning_at (loc, 0, "conversion to void will not access " - "object of type %qT", type); - break; - case ICV_SECOND_OF_COND: - warning_at (loc, 0, "implicit dereference will not access " - "object of type %qT in second operand of " - "conditional expression", type); - break; - case ICV_THIRD_OF_COND: - warning_at (loc, 0, "implicit dereference will not access " - "object of type %qT in third operand of " - "conditional expression", type); - break; - case ICV_RIGHT_OF_COMMA: - warning_at (loc, 0, "implicit dereference will not access " - "object of type %qT in right operand of " - "comma operator", type); - break; - case ICV_LEFT_OF_COMMA: - warning_at (loc, 0, "implicit dereference will not access " - "object of type %qT in left operand of comma " - "operator", type); - break; - case ICV_STATEMENT: - warning_at (loc, 0, "implicit dereference will not access " - "object of type %qT in statement", type); - break; - case ICV_THIRD_IN_FOR: - warning_at (loc, 0, "implicit dereference will not access " - "object of type %qT in for increment expression", - type); - break; - default: - gcc_unreachable (); - } - } + /* Don't load the value if the type needs to be handled by cdtors. */ else if (is_volatile && TREE_ADDRESSABLE (type)) { if (complain & tf_warning) @@ -1386,7 +1340,7 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain) gcc_unreachable (); } } - if (is_reference || !is_volatile || !is_complete || TREE_ADDRESSABLE (type)) + if (!is_volatile || !COMPLETE_TYPE_P (type)) { /* Emit a warning (if enabled) when the "effect-less" INDIRECT_REF operation is stripped off. Note that we don't warn about @@ -1397,8 +1351,8 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain) if (warn_unused_value && implicit != ICV_CAST && (complain & tf_warning) - && !warning_suppressed_p (expr, OPT_Wunused_value) - && !is_reference) + && !warning_suppressed_p (expr, OPT_Wunused_value) + && !REFERENCE_REF_P (expr)) warning_at (loc, OPT_Wunused_value, "value computed is not used"); expr = TREE_OPERAND (expr, 0); if (TREE_CODE (expr) == CALL_EXPR diff --git a/gcc/testsuite/g++.dg/expr/discarded1a.C b/gcc/testsuite/g++.dg/expr/discarded1a.C index 1c4dff4553e..4754f32f716 100644 --- a/gcc/testsuite/g++.dg/expr/discarded1a.C +++ b/gcc/testsuite/g++.dg/expr/discarded1a.C @@ -12,6 +12,5 @@ extern volatile Holder* c; int main() { a; // { dg-message "required from here" } b; // { dg-message "required from here" } - // { dg-warning "implicit dereference will not access object" "" { target *-*-* } .-1 } *c; // { dg-message "required from here" } } diff --git a/gcc/testsuite/g++.dg/expr/volatile2.C b/gcc/testsuite/g++.dg/expr/volatile2.C new file mode 100644 index 00000000000..62e609aee2f --- /dev/null +++ b/gcc/testsuite/g++.dg/expr/volatile2.C @@ -0,0 +1,12 @@ +// Verify we preserve implicit loads of volatile references in a +// discarded-value expression. +// { dg-additional-options "-O -fdump-tree-original -fdump-tree-optimized" } +// { dg-final { scan-tree-dump {\*a} "original" } } +// { dg-final { scan-tree-dump {\*a} "optimized" } } + +struct A { int m; }; +extern volatile A& a; + +int main() { + a; +} diff --git a/gcc/testsuite/g++.old-deja/g++.bugs/900428_01.C b/gcc/testsuite/g++.old-deja/g++.bugs/900428_01.C index a806ef0706e..2b82c64ff73 100644 --- a/gcc/testsuite/g++.old-deja/g++.bugs/900428_01.C +++ b/gcc/testsuite/g++.old-deja/g++.bugs/900428_01.C @@ -46,16 +46,16 @@ void int_test (int i, int *p, volatile int *vp, int &r, volatile int &vr) (void)(i ? r : j); // ok, no warning (void)((void)1, r); // ok, no warning - vr; // { dg-warning "" } reference not accessed - (void)vr; // { dg-warning "" } reference not accessed - (void)(i ? vj : vr); // { dg-warning "" } reference not accessed - (void)(i ? vr : vj); // { dg-warning "" } reference not accessed - (void)((void)1, vr); // { dg-warning "" } reference not accessed + vr; // ok, no warning + (void)vr; // ok, no warning + (void)(i ? vj : vr); // ok, no warning + (void)(i ? vr : vj); // ok, no warning + (void)((void)1, vr); // ok, no warning *ip_fn (); // ok, no warning *vip_fn (); // ok, no warning ir_fn (); // ok, no warning - vir_fn (); // { dg-warning "" } reference not accessed + vir_fn (); // ok, no warning } struct S; @@ -128,16 +128,16 @@ void complete_test (int i, T *p, volatile T *vp, T &r, volatile T &vr) (void)(i ? r : j); // ok, no warning (void)((void)1, r); // ok, no warning - vr; // { dg-warning "" } reference not accessed - (void)vr; // { dg-warning "" } reference not accessed - (void)(i ? vj : vr); // { dg-warning "" } reference not accessed - (void)(i ? vr : vj); // { dg-warning "" } reference not accessed - (void)((void)1, vr); // { dg-warning "" } reference not accessed + vr; // ok, no warning + (void)vr; // ok, no warning + (void)(i ? vj : vr); // ok, no warning + (void)(i ? vr : vj); // ok, no warning + (void)((void)1, vr); // ok, no warning *tp_fn (); // ok, no warning *vtp_fn (); // ok, no warning tr_fn (); // ok, no warning - vtr_fn (); // ok, no warning{ dg-warning "" } reference not accessed + vtr_fn (); // ok, no warning } void extern_test () @@ -160,5 +160,5 @@ void extern_test () esr; // ok, no warning vesr; // { dg-warning "" } incomplete not accessed etr; // ok, no warning - vetr; // { dg-warning "" } reference not accessed + vetr; // ok, no warning } -- 2.42.0.216.gbda494f404