https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90052
Bug ID: 90052
Summary: No -Wtautological-compare warning for (x == 1 && x ==
2)
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: redi at gcc dot gnu.org
Target Milestone: ---
G++ doesn't warn about:
int f(int x)
{
if (x == 1 && x == 2)
return x;
if (x != 1 || x != 2)
return x;
return 0;
}
Clang warns with -Wtautological-compare (but not -Wall -Wextra):
taut.cc:5:14: warning: overlapping comparisons always evaluate to true
[-Wtautological-overlap-compare]
if (x != 1 || x != 2)
~~~~~~~^~~~~~~~~
taut.cc:3:14: warning: overlapping comparisons always evaluate to false
[-Wtautological-overlap-compare]
if (x == 1 && x == 2)
~~~~~~~^~~~~~~~~
2 warnings generated.
It's easy to accidentally write && when you mean || or vice versa, so the
warning is useful.
