https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77292
Bug ID: 77292
Summary: Spurious "warning: logical not is only applied to the
left hand side of comparison"
Product: gcc
Version: 5.4.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: terra at gnome dot org
Target Milestone: ---
The warning introduced in bug 62183 is trigger-happy.
int
foo (int a, int b)
{
// Make it obvious that these are booleans.
a = !!a;
b = !!b;
return !a == b;
}
# gcc --version
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.2) 5.4.0 20160609
Copyright (C) 2015 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
# gcc -c -Wall -O2 bbb.c
bbb.c: In function ‘foo’:
bbb.c:8:13: warning: logical not is only applied to the left hand side of
comparison [-Wlogical-not-parentheses]
return !a == b;
^
This is silly and out-right illogical when "a" and "b" are booleans.
"!a == b" means the same as "!(a == b)", so the warning is pointing out
that I might have meant something else that, upon inspection, is seen
to be the same thing.
Note: by "boolean" I mean an integer with value 0 or 1.
