| Message ID | CADzB+2mah0B-_rJ6zjhSRX+k+cwo4y7OzzwEL71_giz4fkY7EA@mail.gmail.com |
|---|---|
| State | New |
| Headers | show |
On 01/08/2017 01:34 AM, Jason Merrill wrote: > P0292 defines the notion of "discarded statement" which is almost but > not quite the same as "unevaluated operand". This PR shows a case > where we need to be able to tell that we're in a discarded statement > at a lower level than in the parser, so this patch moves the > information about being in a discarded statement from the parser into > saved_scope. I've also added a test for a couple of cases that > demonstrate why we can't just use cp_unevaluated_context. > + if constexpr(sizeof(long long) == sizeof(char*)) > + ; > + else > + sizeof_mismatch<sizeof(long long)>(); This is going to behave differently on 32 and 64 bit HW. Is that intentional? (If so, a comment would be nice) nathan
On 09/01/17 13:49, Nathan Sidwell wrote: > On 01/08/2017 01:34 AM, Jason Merrill wrote: >> P0292 defines the notion of "discarded statement" which is almost but >> not quite the same as "unevaluated operand". This PR shows a case >> where we need to be able to tell that we're in a discarded statement >> at a lower level than in the parser, so this patch moves the >> information about being in a discarded statement from the parser into >> saved_scope. I've also added a test for a couple of cases that >> demonstrate why we can't just use cp_unevaluated_context. > >> + if constexpr(sizeof(long long) == sizeof(char*)) >> + ; >> + else >> + sizeof_mismatch<sizeof(long long)>(); > > This is going to behave differently on 32 and 64 bit HW. Is that intentional? (If so, a comment would be nice) > Indeed I see this test failing when testing aarch64 with -mabi=ilp32. Kyrill > nathan >
On Mon, Jan 09, 2017 at 08:49:25AM -0500, Nathan Sidwell wrote: > On 01/08/2017 01:34 AM, Jason Merrill wrote: > > P0292 defines the notion of "discarded statement" which is almost but > > not quite the same as "unevaluated operand". This PR shows a case > > where we need to be able to tell that we're in a discarded statement > > at a lower level than in the parser, so this patch moves the > > information about being in a discarded statement from the parser into > > saved_scope. I've also added a test for a couple of cases that > > demonstrate why we can't just use cp_unevaluated_context. > > > + if constexpr(sizeof(long long) == sizeof(char*)) > > + ; > > + else > > + sizeof_mismatch<sizeof(long long)>(); > > This is going to behave differently on 32 and 64 bit HW. Is that > intentional? (If so, a comment would be nice) Yeah, it fails on i686-linux and other ILP32 and similar targets. FAIL: g++.dg/cpp1z/constexpr-if10.C (test for excess errors) Could we do e.g. sed -i -e 's/long long/int */g' testsuite/g++.dg/cpp1z/constexpr-if10.C so that it is something where if constexpr will be always true? Jakub
On 01/09/2017 09:03 AM, Jakub Jelinek wrote: > FAIL: g++.dg/cpp1z/constexpr-if10.C (test for excess errors) > > Could we do e.g. > sed -i -e 's/long long/int */g' testsuite/g++.dg/cpp1z/constexpr-if10.C > so that it is something where if constexpr will be always true? that would seem fine to me nathan
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h index 39f5d79..24de346 100644 --- a/gcc/cp/cp-tree.h +++ b/gcc/cp/cp-tree.h @@ -1281,6 +1281,10 @@ struct GTY(()) saved_scope { BOOL_BITFIELD x_processing_explicit_instantiation : 1; BOOL_BITFIELD need_pop_function_context : 1; +/* Nonzero if we are parsing the discarded statement of a constexpr + if-statement. */ + BOOL_BITFIELD discarded_stmt : 1; + int unevaluated_operand; int inhibit_evaluation_warnings; int noexcept_operand; @@ -1341,6 +1345,8 @@ extern GTY(()) struct saved_scope *scope_chain; #define processing_specialization scope_chain->x_processing_specialization #define processing_explicit_instantiation scope_chain->x_processing_explicit_instantiation +#define in_discarded_stmt scope_chain->discarded_stmt + /* RAII sentinel to handle clearing processing_template_decl and restoring it when done. */ diff --git a/gcc/cp/decl2.c b/gcc/cp/decl2.c index a0375ad..435f51f 100644 --- a/gcc/cp/decl2.c +++ b/gcc/cp/decl2.c @@ -5112,7 +5112,7 @@ mark_used (tree decl, tsubst_flags_t complain) } /* If we don't need a value, then we don't need to synthesize DECL. */ - if (cp_unevaluated_operand != 0) + if (cp_unevaluated_operand || in_discarded_stmt) return true; DECL_ODR_USED (decl) = 1; diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c index 57ae064..e8c0642 100644 --- a/gcc/cp/parser.c +++ b/gcc/cp/parser.c @@ -11147,12 +11147,12 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p, /* Outside a template, the non-selected branch of a constexpr if is a 'discarded statement', i.e. unevaluated. */ - bool was_discarded = parser->in_discarded_stmt; + bool was_discarded = in_discarded_stmt; bool discard_then = (cx && !processing_template_decl && integer_zerop (condition)); if (discard_then) { - parser->in_discarded_stmt = true; + in_discarded_stmt = true; ++c_inhibit_evaluation_warnings; } @@ -11166,7 +11166,7 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p, if (discard_then) { THEN_CLAUSE (statement) = NULL_TREE; - parser->in_discarded_stmt = was_discarded; + in_discarded_stmt = was_discarded; --c_inhibit_evaluation_warnings; } @@ -11178,7 +11178,7 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p, && integer_nonzerop (condition)); if (discard_else) { - parser->in_discarded_stmt = true; + in_discarded_stmt = true; ++c_inhibit_evaluation_warnings; } @@ -11235,7 +11235,7 @@ cp_parser_selection_statement (cp_parser* parser, bool *if_p, if (discard_else) { ELSE_CLAUSE (statement) = NULL_TREE; - parser->in_discarded_stmt = was_discarded; + in_discarded_stmt = was_discarded; --c_inhibit_evaluation_warnings; } } @@ -12143,7 +12143,7 @@ cp_parser_jump_statement (cp_parser* parser) expression. */ expr = NULL_TREE; /* Build the return-statement. */ - if (current_function_auto_return_pattern && parser->in_discarded_stmt) + if (current_function_auto_return_pattern && in_discarded_stmt) /* Don't deduce from a discarded return statement. */; else statement = finish_return_stmt (expr); diff --git a/gcc/cp/parser.h b/gcc/cp/parser.h index f242f4c..0994e1e 100644 --- a/gcc/cp/parser.h +++ b/gcc/cp/parser.h @@ -336,10 +336,6 @@ struct GTY(()) cp_parser { a local class. */ bool in_function_body; - /* TRUE if we are parsing a C++17 discarded statement (the non-taken branch - of an if constexpr). */ - bool in_discarded_stmt; - /* Nonzero if we're processing a __transaction_atomic or __transaction_relaxed statement. */ unsigned char in_transaction; diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if10.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if10.C new file mode 100644 index 0000000..64de53f --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if10.C @@ -0,0 +1,16 @@ +// PR c++/79848 +// { dg-options -std=c++1z } + +template <int T> +void sizeof_mismatch() +{ + static_assert(T == 0, "sizeof mismatch"); +} + +int main() +{ + if constexpr(sizeof(long long) == sizeof(char*)) + ; + else + sizeof_mismatch<sizeof(long long)>(); +} diff --git a/gcc/testsuite/g++.dg/cpp1z/constexpr-if11.C b/gcc/testsuite/g++.dg/cpp1z/constexpr-if11.C new file mode 100644 index 0000000..1c6247e --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp1z/constexpr-if11.C @@ -0,0 +1,16 @@ +// Test that discarded statements differ from unevaluated operands in some +// ways. +// { dg-options -std=c++1z } + +struct A { int i; }; + +int main() +{ + if constexpr(true) + ; + else + { + []{}(); + A::i; // { dg-error "non-static" } + } +}
P0292 defines the notion of "discarded statement" which is almost but not quite the same as "unevaluated operand". This PR shows a case where we need to be able to tell that we're in a discarded statement at a lower level than in the parser, so this patch moves the information about being in a discarded statement from the parser into saved_scope. I've also added a test for a couple of cases that demonstrate why we can't just use cp_unevaluated_context. Tested x86_64-pc-linux-gnu, applying to trunk. commit 4d3de5520010cda3bdb47c8a6532e734f09cfc3e Author: Jason Merrill <jason@redhat.com> Date: Fri Jan 6 09:45:02 2017 -0500 PR c++/78948 - instantiation from discarded statement * parser.h (struct cp_parser): Remove in_discarded_stmt field. * cp-tree.h (in_discarded_stmt): Declare it. (struct saved_scope): Add discarded_stmt bitfield. (in_discarded_stmt): New macro. * decl2.c (mark_used): Check it. * parser.c (cp_parser_selection_statement): Adjust. (cp_parser_jump_statement): Adjust.