[Bug c/97748] Preincrement of _Complex gives bogus warning = "value computed is not used"
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97748 Jakub Jelinek changed: What|Removed |Added Resolution|--- |FIXED Status|UNCONFIRMED |RESOLVED --- Comment #5 from Jakub Jelinek --- Fixed for 10.3+.
[Bug c/97748] Preincrement of _Complex gives bogus warning = "value computed is not used"
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97748 --- Comment #4 from CVS Commits --- The releases/gcc-10 branch has been updated by Jakub Jelinek : https://gcc.gnu.org/g:9d488c191c62cb114fa40239c495ac773ff76751 commit r10-9011-g9d488c191c62cb114fa40239c495ac773ff76751 Author: Jakub Jelinek Date: Tue Nov 10 15:56:20 2020 +0100 c, c++: Fix up -Wunused-value on COMPLEX_EXPRs [PR97748] The -Wunused-value warning in both C and C++ FEs (implemented significantly differently between the two) sees the COMPLEX_EXPRs created e.g. for complex pre/post increment and many other expressions as useless and warns about it. For the C warning implementation, on e.g. COMPLEX_EXPR < ++REALPART_EXPR , IMAGPART_EXPR >; would warn even on the IMAGPART_EXPR there alone etc., so what works is check if we'd warn about both operands of COMPLEX_EXPR and if yes, warn on the whole COMPLEX_EXPR, otherwise don't warn. The C++ warning implementation is significantly different and for that one the only warn if both would be warned about doesn't really work, we then miss warnings e.g. about COMPLEX_EXPR > + 1.0e+0, IMAGPART_EXPR >> > The patch replaces the warning_at call with call to the c-family warn_if_unused_value function. On the testcase which after the initial new tests contains pretty much everything from gcc.dg/Wunused-value-1.c both approaches seem to work nicely. 2020-11-10 Jakub Jelinek PR c/97748 gcc/c-family/ * c-common.h (warn_if_unused_value): Add quiet argument defaulted to false. * c-warn.c (warn_if_unused_value): Likewise. Pass it down recursively and just return true instead of warning if it is true. Handle COMPLEX_EXPR. gcc/cp/ * cvt.c (convert_to_void): Check (complain & tf_warning) in the outer if rather than twice times in the inner one. Use warn_if_unused_value. Formatting fix. gcc/testsuite/ * c-c++-common/Wunused-value-1.c: New test. (cherry picked from commit ea4fb4eaacbd2c954d78d7f8e9f03c7be739)
[Bug c/97748] Preincrement of _Complex gives bogus warning = "value computed is not used"
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97748 --- Comment #3 from CVS Commits --- The master branch has been updated by Jakub Jelinek : https://gcc.gnu.org/g:ea4fb4eaacbd2c954d78d7f8e9f03c7be739 commit r11-4878-gea4fb4eaacbd2c954d78d7f8e9f03c7be739 Author: Jakub Jelinek Date: Tue Nov 10 15:56:20 2020 +0100 c, c++: Fix up -Wunused-value on COMPLEX_EXPRs [PR97748] The -Wunused-value warning in both C and C++ FEs (implemented significantly differently between the two) sees the COMPLEX_EXPRs created e.g. for complex pre/post increment and many other expressions as useless and warns about it. For the C warning implementation, on e.g. COMPLEX_EXPR < ++REALPART_EXPR , IMAGPART_EXPR >; would warn even on the IMAGPART_EXPR there alone etc., so what works is check if we'd warn about both operands of COMPLEX_EXPR and if yes, warn on the whole COMPLEX_EXPR, otherwise don't warn. The C++ warning implementation is significantly different and for that one the only warn if both would be warned about doesn't really work, we then miss warnings e.g. about COMPLEX_EXPR > + 1.0e+0, IMAGPART_EXPR >> > The patch replaces the warning_at call with call to the c-family warn_if_unused_value function. On the testcase which after the initial new tests contains pretty much everything from gcc.dg/Wunused-value-1.c both approaches seem to work nicely. 2020-11-10 Jakub Jelinek PR c/97748 gcc/c-family/ * c-common.h (warn_if_unused_value): Add quiet argument defaulted to false. * c-warn.c (warn_if_unused_value): Likewise. Pass it down recursively and just return true instead of warning if it is true. Handle COMPLEX_EXPR. gcc/cp/ * cvt.c (convert_to_void): Check (complain & tf_warning) in the outer if rather than twice times in the inner one. Use warn_if_unused_value. Formatting fix. gcc/testsuite/ * c-c++-common/Wunused-value-1.c: New test.
[Bug c/97748] Preincrement of _Complex gives bogus warning = "value computed is not used"
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97748
--- Comment #2 from Jakub Jelinek ---
Untested WIP patch, though C++ FE needs some extra work:
--- gcc/c-family/c-common.h.jj 2020-11-03 11:15:07.170681001 +0100
+++ gcc/c-family/c-common.h 2020-11-07 09:37:48.597233063 +0100
@@ -1362,7 +1362,7 @@ extern void warn_tautological_cmp (const
tree, tree);
extern void warn_logical_not_parentheses (location_t, enum tree_code, tree,
tree);
-extern bool warn_if_unused_value (const_tree, location_t);
+extern bool warn_if_unused_value (const_tree, location_t, bool = false);
extern bool strict_aliasing_warning (location_t, tree, tree);
extern void sizeof_pointer_memaccess_warning (location_t *, tree,
vec *, tree *,
--- gcc/c-family/c-warn.c.jj2020-10-26 10:53:56.533885147 +0100
+++ gcc/c-family/c-warn.c 2020-11-07 09:40:51.011170825 +0100
@@ -585,7 +585,7 @@ warn_logical_not_parentheses (location_t
(potential) location of the expression. */
bool
-warn_if_unused_value (const_tree exp, location_t locus)
+warn_if_unused_value (const_tree exp, location_t locus, bool quiet)
{
restart:
if (TREE_USED (exp) || TREE_NO_WARNING (exp))
@@ -633,7 +633,7 @@ warn_if_unused_value (const_tree exp, lo
goto restart;
case COMPOUND_EXPR:
- if (warn_if_unused_value (TREE_OPERAND (exp, 0), locus))
+ if (warn_if_unused_value (TREE_OPERAND (exp, 0), locus, quiet))
return true;
/* Let people do `(foo (), 0)' without a warning. */
if (TREE_CONSTANT (TREE_OPERAND (exp, 1)))
@@ -648,6 +648,13 @@ warn_if_unused_value (const_tree exp, lo
return false;
goto warn;
+case COMPLEX_EXPR:
+ /* Warn only if both operands are unused. */
+ if (warn_if_unused_value (TREE_OPERAND (exp, 0), locus, true)
+ && warn_if_unused_value (TREE_OPERAND (exp, 1), locus, true))
+ goto warn;
+ return false;
+
case INDIRECT_REF:
/* Don't warn about automatic dereferencing of references, since
the user cannot control it. */
@@ -671,6 +678,8 @@ warn_if_unused_value (const_tree exp, lo
return false;
warn:
+ if (quiet)
+ return true;
return warning_at (locus, OPT_Wunused_value, "value computed is not
used");
}
}
--- gcc/testsuite/c-c++-common/Wunused-value-1.c.jj 2020-11-07
09:51:46.407757100 +0100
+++ gcc/testsuite/c-c++-common/Wunused-value-1.c2020-11-07
10:15:34.295574782 +0100
@@ -0,0 +1,33 @@
+/* PR c/97748 */
+/* { dg-do compile } */
+/* { dg-options "-Wunused-value" } */
+
+double _Complex f ();
+double _Complex *p;
+
+double _Complex
+foo (double _Complex x)
+{
+ ++x; /* { dg-bogus "value computed is not used" } */
+ --x; /* { dg-bogus "value computed is not used" } */
+ x += 1; /* { dg-bogus "value computed is not used" } */
+ x += 1.0iF; /* { dg-bogus "value computed is not used" } */
+ x++; /* { dg-bogus "value computed is not used" } */
+ x--; /* { dg-bogus "value computed is not used" } */
+ x + 1; /* { dg-warning "value computed is not used" } */
+ (void) (x + 1); /* { dg-bogus "value computed is not used" } */
+ 1 + f ();/* { dg-warning "value computed is not used" } */
+ f () + f (); /* { dg-warning "value computed is not used" }
*/
+ f () + f (), f (); /* { dg-warning "value computed is not used" } */
+ f ();
+ (void) f ();
+ *p++;/* { dg-warning "value computed is not used" }
*/
+ ++*p;/* { dg-bogus "value computed is not used" } */
+ (*p ? f () : 0);
+ ({ f (); });
+ ({ f () + 1; });
+ ({ f (); 0; });
+ ({ f () + 1; 0; }); /* { dg-warning "value computed is not used" } */
+ 1 + ({ f (); }); /* { dg-warning "value computed is not used" } */
+ return x;
+}
[Bug c/97748] Preincrement of _Complex gives bogus warning = "value computed is not used"
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97748
Jakub Jelinek changed:
What|Removed |Added
CC||jakub at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek ---
Adjusted testcase:
/* PR c/97748 */
/* { dg-do compile } */
/* { dg-options "-Wunused-value" } */
double _Complex
foo (double _Complex x)
{
++x; /* { dg-bogus "value computed is not used" } */
return x;
}
double _Complex
bar (double _Complex x)
{
--x; /* { dg-bogus "value computed is not used" } */
return x;
}
The tree that is not used is a COMPLEX_EXPR:
(void) COMPLEX_EXPR < ++REALPART_EXPR , IMAGPART_EXPR >
which would be used only if the result of the post increment or decrement would
be actually used.
So, either we should mark the COMPLEX_EXPR created for the pre-increments
TREE_NO_WARNING, or the -Wunused-value would need to look through the
COMPLEX_EXPR.
