https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89131
Bug ID: 89131
Summary: redundant -Wabsolute-value when -Wconversion is used
and vice versa
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
The newly introduced -Wabsolute-value warning (also by -Wextra) partly
duplicates the functionality of the -Wconversion warning (disabled by default).
Enabling both options leads to duplicate diagnostics for the same problem, as
the example below shows.
Normally, to avoid drowning users in excessive complaints GCC tries to avoid
issuing multiple warnings for the same construct, even if the warnings are
slightly different (e.g., -Warray-bounds, -Wrestrict, and -Wstringop-overflow
for basically the same bug).
In this case, either this particular instance of -Wabsolute-value should be
disabled when -Wconversion is enabled or (perhaps preferably), the other way
around.
$ cat u.c && gcc -S -Wall -Wextra -Wconversion u.c
int f (long x)
{
return __builtin_abs (x);
}
u.c: In function ‘f’:
u.c:3:10: warning: absolute value function ‘__builtin_abs’ given an argument of
type ‘long int’ but has parameter of type ‘int’ which may cause truncation of
value [-Wabsolute-value]
3 | return __builtin_abs (x);
| ^~~~~~~~~~~~~
u.c:3:25: warning: conversion from ‘long int’ to ‘int’ may change value
[-Wconversion]
3 | return __builtin_abs (x);
| ^
