Hi! In cp_parser_expression for comma operator I've used a short path where instead of calling build_x_compound_expr #embed number times it is called just 3 times, for the CPP_NUMBER added by the preprocessor at the start, last byte from CPP_EMBED and then CPP_NUMBER added by libcpp at the end, enough to make sure -Wunused-value reports something, but not bothering users with millions of -Wunused-value warnings and spending too much compile time on it when they use a very large #embed.
As the following testcases show, that is ok for C or for C++ if the expression before it is known not to have OVERLOAD_TYPE_P (common case is INTEGER_TYPE I guess), but doesn't work well in case one uses overloaded comma operator. In that case we just have to call build_x_compound_expr the right number of times, even if it is a lot. I think I don't need to test for !expression, because the preprocessor should guarantee that CPP_EMBED is preceded by CPP_NUMBER CPP_COMMA tokens. Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/15.3? 2026-01-21 Jakub Jelinek <[email protected]> PR c++/123737 * parser.cc (cp_parser_expression): Don't handle CPP_EMBED just as the last byte in it if expression has or might have overloaded type. In that case call build_x_compound_expr for each byte in CPP_EMBED separately. * g++.dg/cpp/embed-28.C: New test. * g++.dg/parse/comma3.C: New test. --- gcc/cp/parser.cc.jj 2026-01-20 01:13:20.324260446 +0100 +++ gcc/cp/parser.cc 2026-01-21 14:04:32.086336386 +0100 @@ -12132,10 +12132,24 @@ cp_parser_expression (cp_parser* parser, and one CPP_NUMBER plus CPP_COMMA before it and one CPP_COMMA plus CPP_NUMBER after it is guaranteed by the preprocessor. Thus, parse the whole CPP_EMBED just - as a single INTEGER_CST, the last byte in it. */ + as a single INTEGER_CST, the last byte in it. Though, + don't use that shortcut if the comma operator could be + overloaded. */ tree raw_data = cp_lexer_peek_token (parser->lexer)->u.value; location_t loc = cp_lexer_peek_token (parser->lexer)->location; cp_lexer_consume_token (parser->lexer); + if (OVERLOAD_TYPE_P (TREE_TYPE (expression)) + || type_dependent_expression_p (expression)) + for (unsigned i = 0; i < RAW_DATA_LENGTH (raw_data) - 1U; ++i) + { + assignment_expression + = *raw_data_iterator (raw_data, i); + assignment_expression.set_location (loc); + expression + = build_x_compound_expr (loc, expression, + assignment_expression, NULL_TREE, + complain_flags (decltype_p)); + } assignment_expression = *raw_data_iterator (raw_data, RAW_DATA_LENGTH (raw_data) - 1); assignment_expression.set_location (loc); --- gcc/testsuite/g++.dg/cpp/embed-28.C.jj 2026-01-21 14:11:14.617520864 +0100 +++ gcc/testsuite/g++.dg/cpp/embed-28.C 2026-01-21 14:11:01.121749695 +0100 @@ -0,0 +1,19 @@ +// PR c++/123737 +// { dg-do run } +// { dg-options "--embed-dir=${srcdir}/c-c++-common/cpp/embed-dir" } + +struct A { + A (int x) : a (0), e (x) {} + unsigned long a, e; + A &operator, (int) { ++a; return *this; } + ~A () { if (a != e) __builtin_abort (); } +}; + +int +main () +{ + A a = 231; + a, +#embed <magna-carta.txt> limit (231) + ; +} --- gcc/testsuite/g++.dg/parse/comma3.C.jj 2026-01-21 14:08:53.834908004 +0100 +++ gcc/testsuite/g++.dg/parse/comma3.C 2026-01-21 12:15:02.334948163 +0100 @@ -0,0 +1,22 @@ +// PR c++/123737 +// { dg-do run } + +struct A { + A (int x) : a (0), e (x) {} + unsigned long a, e; + A &operator, (int) { ++a; return *this; } + ~A () { if (a != e) __builtin_abort (); } +}; + +int +main () +{ + A a = 131; + a, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, + 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0; +} Jakub
