Hi!
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.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2020-08-14 Jakub Jelinek <ja...@redhat.com>
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.jj 2020-07-28 15:39:09.672760847 +0200
+++ gcc/c/c-parser.c 2020-08-13 15:41:09.476861020 +0200
@@ -8686,7 +8686,7 @@ c_parser_generic_selection (c_parser *pa
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 *pa
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 *pa
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 *pa
c_parser_consume_token (parser);
}
+ unsigned int ix;
+ struct c_generic_association *iter;
+ FOR_EACH_VEC_ELT (associations, ix, iter)
+ if (ix != 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",
--- gcc/testsuite/gcc.dg/Wunused-var-4.c.jj 2020-08-13 18:36:35.608060608
+0200
+++ gcc/testsuite/gcc.dg/Wunused-var-4.c 2020-08-13 18:36:48.866880017
+0200
@@ -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);
+}
Jakub
