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* [gcc(refs/vendors/redhat/heads/gcc-8-branch)] c: Fix -Wunused-but-set-* warning with _Generic [PR96571]
@ 2020-09-17 17:24 Jakub Jelinek
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From: Jakub Jelinek @ 2020-09-17 17:24 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:b87e46bffda7134586ff93e5f7709a5c9a1a0eae
commit b87e46bffda7134586ff93e5f7709a5c9a1a0eae
Author: Jakub Jelinek <jakub@redhat.com>
Date: Tue Aug 18 07:51:58 2020 +0200
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 <jakub@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.
(cherry picked from commit 6d42cbe5ad7a7b46437f2576c9920e44dc14b386)
Diff:
---
gcc/c/c-parser.c | 19 +++++++++++++------
gcc/testsuite/gcc.dg/Wunused-var-4.c | 33 +++++++++++++++++++++++++++++++++
2 files changed, 46 insertions(+), 6 deletions(-)
diff --git a/gcc/c/c-parser.c b/gcc/c/c-parser.c
index 75ef0a437a7..bea4dd2a779 100644
--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -7585,7 +7585,7 @@ 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;
@@ -7620,6 +7620,7 @@ 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. */
@@ -7719,18 +7720,18 @@ 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
{
@@ -7748,13 +7749,19 @@ 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);
+}
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