https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70181
Bug ID: 70181
Summary: missing -Wtautological-compare for constant
expressions
Product: gcc
Version: 6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
According to the documentation for -Wtautological-compare:
Warn if a self-comparison always evaluates to true or false. This warning
detects various mistakes such as: ...
all three equality expressions in the program below should be diagnosed, yet
only the first on in function f() is. Clang diagnoses all three as expected.
Either the other expressions should be diagnosed or the documentation clarified
that the warning is deliberately not issued for constant expressions.
$ cat v.c && /home/msebor/build/gcc-trunk-svn/gcc/xgcc
-B/home/msebor/build/gcc-trunk-svn/gcc -S -Wall -Wextra -Wpedantic -o/dev/null
-xc++ v.c
int f (int i) { if (i == i) return 1; return 0; }
enum { i = 0 };
const bool b0 = i == i;
constexpr int j = 0;
constexpr bool b1 = j == j;
v.c: In function ‘int f(int)’:
v.c:1:23: warning: self-comparison always evaluates to true
[-Wtautological-compare]
int f (int i) { if (i == i) return 1; return 0; }
~~^~~~
