c++: Fix up [[nodiscard]] on ctors on targetm.cxx.cdtor_returns_this targets [PR99362]
In the P1771R1 changes JeanHeyd reverted part of Alex' PR88146 fix, but that seems to be incorrect to me. Where P1771R1 suggests warnings for [[nodiscard]] on constructors is handled in a different place - in particular the TARGET_EXPR handling of convert_to_void. When we have CALL_EXPR of a ctor, on most arches that call has void return type and so returns early, and on arm where the ctor returns the this pointer it is undesirable to warn as it warns about all ctor calls, not just the ones where it should warn. The P1771R1 changes added a test for this, but as it was given *.c extension rather than *.C, the test was never run and so this didn't get spotted immediately. The test also had a bug, (?n) can't be used in dg-warning/dg-error because those are implemented by prepending some regexp before the user provided one and (?n) must come at the start of the regexp. Furthermore, while -ftrack-macro-expansion=0 is useful in one nodiscard test which uses macros, I don't see how it would be relevant to all the other cpp2a/nodiscard* tests which don't use any macros. 2021-03-04 Jakub Jelinek <jakub@redhat.com> PR c++/88146 PR c++/99362 gcc/cp/ * cvt.c (convert_to_void): Revert 2019-10-17 changes. Clarify comment. gcc/testsuite/ * g++.dg/cpp2a/nodiscard-constructor.c: Renamed to ... * g++.dg/cpp2a/nodiscard-constructor1.C: ... this. Remove -ftrack-macro-expansion=0 from dg-options. Don't use (?n) in dg-warning regexps, instead replace .* with \[^\n\r]*. * g++.dg/cpp2a/nodiscard-constructor2.C: New test. * g++.dg/cpp2a/nodiscard-reason-only-one.C: Remove -ftrack-macro-expansion=0 from dg-options. * g++.dg/cpp2a/nodiscard-reason-nonstring.C: Likewise. * g++.dg/cpp2a/nodiscard-once.C: Likewise.
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gcc/cp/cvt.c
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gcc/cp/cvt.c
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@ -1231,12 +1231,14 @@ convert_to_void (tree expr, impl_conv_void implicit, tsubst_flags_t complain)
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case CALL_EXPR: /* We have a special meaning for volatile void fn(). */
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/* cdtors may return this or void, depending on
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targetm.cxx.cdtor_returns_this, but this shouldn't affect our
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decisions here: neither nodiscard warnings (nodiscard cdtors
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are nonsensical), nor should any constexpr or template
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instantiations be affected by an ABI property that is, or at
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least ought to be transparent to the language. */
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decisions here: neither nodiscard warnings (nodiscard dtors
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are nonsensical and ctors have a different behavior with that
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attribute that is handled in the TARGET_EXPR case), nor should
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any constexpr or template instantiations be affected by an ABI
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property that is, or at least ought to be transparent to the
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language. */
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if (tree fn = cp_get_callee_fndecl_nofold (expr))
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if (DECL_DESTRUCTOR_P (fn))
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if (DECL_CONSTRUCTOR_P (fn) || DECL_DESTRUCTOR_P (fn))
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return expr;
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if (complain & tf_warning)
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@ -1,6 +1,6 @@
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/* nodiscard attribute tests */
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/* { dg-do compile { target c++20 } } */
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/* { dg-options "-O -ftrack-macro-expansion=0" } */
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/* { dg-options "-O" } */
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struct A { [[nodiscard("bad constructor")]] A() {} };
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struct B { [[nodiscard]] B() {} };
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@ -8,6 +8,6 @@ struct B { [[nodiscard]] B() {} };
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void
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test (void)
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{
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A{}; /* { dg-warning "(?n)nodiscard.*bad constructor" } */
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B{}; /* { dg-warning "(?n)nodiscard" } */
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A{}; /* { dg-warning "nodiscard\[^\n\r]*bad constructor" } */
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B{}; /* { dg-warning "nodiscard" } */
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}
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@ -0,0 +1,17 @@
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// PR c++/99362
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// { dg-do compile { target c++20 } }
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struct S {
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[[nodiscard]] S() {}
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S(int) {}
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};
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int main()
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{
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S s;
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S(); // { dg-warning "ignoring return value" }
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(void)(S());
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S t = 1;
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S(1);
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(void)(S(1));
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}
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@ -1,6 +1,6 @@
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/* nodiscard attribute tests */
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/* { dg-do compile { target c++20 } } */
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/* { dg-options "-O -ftrack-macro-expansion=0" } */
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/* { dg-options "-O" } */
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[[nodiscard, nodiscard]] int check1 (void); // { dg-warning "specified multiple times" }
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@ -1,6 +1,6 @@
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/* nodiscard attribute tests */
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/* { dg-do compile { target c++20 } } */
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/* { dg-options "-O -ftrack-macro-expansion=0" } */
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/* { dg-options "-O" } */
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[[nodiscard(123)]] int check1 (void); /* { dg-error "nodiscard\[^\n\r]*must be a string constant" } */
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@ -1,6 +1,6 @@
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/* nodiscard attribute tests */
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/* { dg-do compile { target c++20 } } */
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/* { dg-options "-O -ftrack-macro-expansion=0" } */
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/* { dg-options "-O" } */
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[[nodiscard("not", "allowed")]] int check1 (void); /* { dg-error "wrong number of arguments.\[^\n\r]*nodiscard" } */
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