From 6d42cbe5ad7a7b46437f2576c9920e44dc14b386 Mon Sep 17 00:00:00 2001 From: Jakub Jelinek Date: Tue, 18 Aug 2020 07:51:58 +0200 Subject: [PATCH] c: Fix -Wunused-but-set-* warning with _Generic [PR96571] The following testcase shows various problems with -Wunused-but-set* warnings and _Generic construct. I think it is best to treat the selector and the ignored expressions as (potentially) read, because when they are parsed, the vars in there are already marked as TREE_USED. 2020-08-18 Jakub Jelinek PR c/96571 * c-parser.c (c_parser_generic_selection): Change match_found from bool to int, holding index of the match. Call mark_exp_read on the selector expression and on expressions other than the selected one. * gcc.dg/Wunused-var-4.c: New test. --- gcc/c/c-parser.c | 19 +++++++++++----- gcc/testsuite/gcc.dg/Wunused-var-4.c | 33 ++++++++++++++++++++++++++++ 2 files changed, 46 insertions(+), 6 deletions(-) create mode 100644 gcc/testsuite/gcc.dg/Wunused-var-4.c diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c index 7961cbc98bb..a8bc301ffad 100644 --- a/gcc/c/c-parser.c +++ b/gcc/c/c-parser.c @@ -8686,7 +8686,7 @@ c_parser_generic_selection (c_parser *parser) struct c_expr selector, error_expr; tree selector_type; struct c_generic_association matched_assoc; - bool match_found = false; + int match_found = -1; location_t generic_loc, selector_loc; error_expr.original_code = ERROR_MARK; @@ -8721,6 +8721,7 @@ c_parser_generic_selection (c_parser *parser) c_parser_skip_until_found (parser, CPP_CLOSE_PAREN, NULL); return selector; } + mark_exp_read (selector.value); selector_type = TREE_TYPE (selector.value); /* In ISO C terms, rvalues (including the controlling expression of _Generic) do not have qualified types. */ @@ -8820,18 +8821,18 @@ c_parser_generic_selection (c_parser *parser) if (assoc.type == NULL_TREE) { - if (!match_found) + if (match_found < 0) { matched_assoc = assoc; - match_found = true; + match_found = associations.length (); } } else if (comptypes (assoc.type, selector_type)) { - if (!match_found || matched_assoc.type == NULL_TREE) + if (match_found < 0 || matched_assoc.type == NULL_TREE) { matched_assoc = assoc; - match_found = true; + match_found = associations.length (); } else { @@ -8849,13 +8850,19 @@ c_parser_generic_selection (c_parser *parser) c_parser_consume_token (parser); } + unsigned int ix; + struct c_generic_association *iter; + FOR_EACH_VEC_ELT (associations, ix, iter) + if (ix != (unsigned) match_found) + mark_exp_read (iter->expression.value); + if (!parens.require_close (parser)) { c_parser_skip_until_found (parser, CPP_CLOSE_PAREN, NULL); return error_expr; } - if (!match_found) + if (match_found < 0) { error_at (selector_loc, "%<_Generic%> selector of type %qT is not " "compatible with any association", diff --git a/gcc/testsuite/gcc.dg/Wunused-var-4.c b/gcc/testsuite/gcc.dg/Wunused-var-4.c new file mode 100644 index 00000000000..08ddcf4407e --- /dev/null +++ b/gcc/testsuite/gcc.dg/Wunused-var-4.c @@ -0,0 +1,33 @@ +/* PR c/96571 */ +/* { dg-do compile } */ +/* { dg-options "-std=c99 -O2 -Wunused-but-set-variable" } */ + +enum E { V }; + +int +foo (void) +{ + enum E v; /* { dg-bogus "set but not used" } */ + return _Generic (v, enum E : 0); +} + +int +bar (void) +{ + int a = 0; /* { dg-bogus "set but not used" } */ + return _Generic (0, int : a); +} + +int +baz (void) +{ + int a; /* { dg-bogus "set but not used" } */ + return _Generic (0, long long : a, int : 0); +} + +int +qux (void) +{ + int a; /* { dg-bogus "set but not used" } */ + return _Generic (0, long long : a, default: 0); +} -- 2.30.2