[PATCH] Make -Wint-in-bool-context warn on suspicious shift ops

[Bernd Edlinger]

On 09/27/16 16:42, Jason Merrill wrote:
> On Tue, Sep 27, 2016 at 10:28 AM, Bernd Edlinger
> <bernd.edlinger@hotmail.de> wrote:
>> On 09/27/16 16:10, Florian Weimer wrote:
>>> * Bernd Edlinger:
>>>
>>>>> “0 << 0” is used in a similar context, to create a zero constant for a
>>>>> multi-bit subfield of an integer.
>>>>>
>>>>> This example comes from GDB, in bfd/elf64-alpha.c:
>>>>>
>>>>> |   insn = INSN_ADDQ | (16 << 21) | (0 << 16) | (0 << 0);
>>>>>
>>>>
>>>> Of course that is not a boolean context, and will not get a warning.
>>>>
>>>> Question is if "if (1 << 0)" is possibly a miss-spelled "if (1 < 0)".
>>>>
>>>> Maybe 1 and 0 come from macro expansion....
>>>
>>> But what's the intent of treating 1 << 0 and 0 << 0 differently in the
>>> patch, then?
>>
>> I am not sure if it was a good idea.
>>
>> I saw, we had code of the form
>> bool flag = 1 << 2;
>>
>> another value LOOKUP_PROTECT is  1 << 0, and
>> bool flag = 1 << 0;
>>
>> would at least not overflow the allowed value range of a boolean.
>
> Assigning a bit mask to a bool variable is still probably not what was
> intended, even if it doesn't change the value.
>

That works for me too.
I can simply remove that exception.


Bernd.