shift-count-overflow possible issue on 64bit type

[Jonny Grant]

On 25/11/2019 12:02, Cristiano Di Buduo wrote:
>>
>> On Sat, 23 Nov 2019 at 13:56, Jonny Grant <
>> jg@jguk.org
>>  <mailto:jg@jguk.org>
>> > wrote:
>>>
>>> I see on my 64bit Ubuntu PC that size_t is 8 bytes, that is 64bits,
>>> however I see a warning:
>>>
>>> $ g++-8 -Wall -Wextra -o size_t size_t.cpp
>>> size_t.cpp: In function ‘int main()’:
>>> size_t.cpp:11:21: warning: left shift count >= width of type
>>> [-Wshift-count-overflow]
>>>        size_t big = 1<<40;
>>>                        ^~
>>>
>>>
>>>
>>> Same on Godbolt trunk.
>>> Is this an issue?
>>
>> Why do you expect a different result for these?
>>
>> A small = 1 << 40;
>> B big = 1 << 40;
>>
>> In both cases the expression is 1 << 40, the type of A or B is irrelevant.
> 
> And the default type of a numeric constant is always int. (32 bits).
> To make the warning go away, typecast the '1' to a size_t first.

Thank you for your replies. I mistakenly expected it to use the size_t type.

I filed a ticket, for GCC to make a suggestion that was appropriate ie. 1UL
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92659

And some other related that I thought of:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92660
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92642

Jonny