https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89107
Bug ID: 89107
Summary: -Wconversion warning is not appropriate since
conversion doesn't alter value, because of mask
entered before.
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: mareksz1958 at wp dot pl
Target Milestone: ---
Such code is failing to compile on 2):
union U {
unsigned int a:20;
};
int main() {
union U u;
unsigned int val = 0xaabbc000;
u.a = val & 0xfffff; // 1) works
u.a = (val >> 12) & 0xfffff; // 2) doesn't
}
Because of the shift the compiler refuses to accept the conversion. And
complains in the following way:
$ gcc wconv.c -Wconversion -Werror
wconv.c: In function ‘main’:
wconv.c:10:11: error: conversion to ‘unsigned int:20’ from ‘unsigned int’ may
alter its value [-Werror=conversion]
u.a = (val >> 12) & 0xfffff; /* 2) doesn't */
^
cc1: all warnings being treated as errors
Clang is compiling following code successfully. Seems like there is some
off-by-one bug; Mask 0x7ffff works without warnings/errors.
