[lld] r233088 - [Mips] Suppress "right shift by too large amount" warning

[Simon Atanasyan]

On Tue, Mar 24, 2015 at 8:35 PM, David Blaikie <dblaikie at gmail.com> wrote:
>
> On Tue, Mar 24, 2015 at 10:28 AM, Simon Atanasyan <simon at atanasyan.com>
> wrote:
>>
>> On Tue, Mar 24, 2015 at 7:16 PM, David Blaikie <dblaikie at gmail.com> wrote:
>> >
>> > On Tue, Mar 24, 2015 at 8:49 AM, Simon Atanasyan <simon at atanasyan.com>
>> > wrote:
>> >>
>> >> Author: atanasyan
>> >> Date: Tue Mar 24 10:49:59 2015
>> >> New Revision: 233088
>> >>
>> >> URL: http://llvm.org/viewvc/llvm-project?rev=233088&view=rev
>> >> Log:
>> >> [Mips] Suppress "right shift by too large amount" warning
>> >>
>> >> Visual C++ shows the "right shift by too large amount" warning if
>> >> `MipsELFReference` is instantiated for 32-bit target and
>> >> `Elf_Rel_Impl::getType`
>> >> method has `unsigned char` return type. We can freely suppress the
>> >> warning
>> >> in
>> >> that case because MIPS 32-bit ABI does not pack multiple relocation
>> >> types
>> >> into
>> >> the single field `r_type` and the `MipsELFReference::_tag` should be
>> >> always
>> >> zero in that case.
>> >
>> >
>> > Can we just disable the MSVC warning if it's wrong, then?
>>
>> I thought about an alternative solution - fix Elf_Rel_Impl::getType()
>> method so all its variants have the same return type uint32_t. Any
>> objections against this idea?
>
> It still doesn't seem to improve anything - if getType() still only returns
> a number 0-255, the shift still is a zero-ing action. Hiding it from the
> compiler doesn't seem to change anything in the semantics of the operation &
> just obscures things further... seems to me, at least.

The getType() does not always return 0-255. In case of 32-bit variant
of Elf_Rel_Impl it does. In case of 64-bit variant it returns 32-bit
integer which can be split up to four parts. In my case I extract
lower 8 bits and high 24 bits.

-- 
Simon Atanasyan