https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70389
Bug ID: 70389
Summary: uint_16t left shift with -Wconversion produces
incorrect warning
Product: gcc
Version: 4.8.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: bobgmeyers at muchomail dot com
Target Milestone: ---
This code:
int
main(void){
uint16_t x;
x=5;
do{
x<<=1U;
x++;
}while(1);
}
The code obviously outputs nothing, but this is just an example of this bug
which happens in every case as described below.
with -Wconversion it produces:
warning: conversion to ‘uint16_t’ from ‘int’ may alter its value [-Wconversion]
x<<=1U;
How on earth could x<<1U end up being an int? x isn't signed and 1U isn't
signed (and according to the spec, the type of 1U is not relevant to the type
of x<<1U). I tried uint32_t and the error went away, so it looks like a problem
with uint16_t. Right shift is also OK.
Might relate to:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59840
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=34389
