https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120359
Bug ID: 120359
Summary: -Wtype-limits misses a warning when comparing enums
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Keywords: diagnostic, testsuite-fail, xfail
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
CC: dnovillo at gcc dot gnu.org, gcc-bugs at gcc dot gnu.org,
manu at gcc dot gnu.org, pinskia at gcc dot gnu.org
Depends on: 33738
Blocks: 89129, 33702
Target Milestone: ---
+++ This bug was initially created as a clone of Bug #33738 +++
This testcase (g++.dg/warn/pr33738.C) was xfailed at r7-3163-g973625a04b3d93
and then the code which did the warning was removed at r13-4277-gca0be1bbedd637
.
The original bug report follows:
This was found on GCC 4.2.1. In this test case, VRP quietly folds a comparison
between an enum type and a constant value that the enum type can never take.
With -Wtype-limits, this should give the warning:
comparison always false due to limited range of data type
extern void link_error (void);
enum Alpha {
ZERO = 0, ONE, TWO, THREE
};
Alpha a2;
int m1 = -1;
int GetM1() {
return m1;
}
int main() {
a2 = static_cast<Alpha>(GetM1());
if (a2 == -1) { <-- VRP should warn when folding this.
link_error ();
}
return 0;
}
This is not warned by the front end because we promote -1 to the same type as
a2. But during VRP, we *do* fold the predicate, so warning when -Wtype-limits
is given in this case would be a good QOI feature.
I have a patch in the works to make VRP warn when it linearizes this predicate.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=33702
[Bug 33702] [meta-bug] GCC 4.4 pending patches
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=33738
[Bug 33738] -Wtype-limits misses a warning when comparing enums
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89129
[Bug 89129] [meta-bug] bogus/missing -Wtype-limits warnings
