[PATCH] Pack MCSymbol flags and common alignment

[Pete Cooper]

> On Jun 29, 2015, at 12:38 PM, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
> 
> LGTM
Thanks!  r241115.

Pete
> 
> On 26 June 2015 at 16:02, Pete Cooper <peter_cooper at apple.com> wrote:
>> 
>>> On Jun 22, 2015, at 10:24 PM, Pete Cooper <peter_cooper at apple.com> wrote:
>>> 
>>> 
>>>> On Jun 22, 2015, at 9:35 PM, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
>>>> 
>>>> Or use one fewer bit for ELF. Nothing is going to align a common to 4 GB :-)
>>> If only that were true, but i’m sure someone will be crazy enough to write an asm test doing just that :)
>>> 
>>> ...
>>>> 
>>>> On 23 June 2015 at 00:23, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
>>>>> Another option would be to use one of the low bits it SectionOrFragment.
>>> I like this solution.  Will get a patch ready tomorrow.
>> Sorry, tomorrow ended up being a few days.
>> 
>> How does this look for the packing a bit in to SectionOrFragment?
>> 
>> 
>> 
>>> 
>>> Pete
>>>>> 
>>>>> With that you could keep 5 bits in the base for common.
>>>>> 
>>>>> 
>>>>> 
>>>>> On 22 June 2015 at 19:19, Pete Cooper <peter_cooper at apple.com> wrote:
>>>>>> I should say, i forgot to clang-format this.  I’ll of course do that before commit as there’s a bunch of 80-cols violations right now.
>>>>>> 
>>>>>> Pete
>>>>>>> On Jun 22, 2015, at 4:05 PM, Pete Cooper <peter_cooper at apple.com> wrote:
>>>>>>> 
>>>>>>> Hi Rafael
>>>>>>> 
>>>>>>> MCSymbol has 32-bits of flags and 32-bits of common alignment.
>>>>>>> 
>>>>>>> However, we only need to represent power of 2 alignments, and no subclasses need more than 16 bits of flags.  We also have 20 bits of bitfields remaining unused.
>>>>>>> 
>>>>>>> This patch takes those 20-bits and exposes them as SubclassData.
>>>>>>> 
>>>>>>> On COFF, we used 16-bits for flags and the remainder are unused.
>>>>>>> On ELF, we used 5 bits to store the log2(align) which allows alignments up to 2^31, i.e., any power of 2 which fits in an unsigned.  The remaining 15 are enough for the ELF flags.
>>>>>>> On MachO, we need 16-bits for flags, and the remaining 4-bits are enough for 2^15 which MCSymbolMachO::getEncodedFlags() already asserted we didn’t exceed.
>>>>>>> 
>>>>>>> This ultimately gets MCSymbol down to 24-bits for the base class.  I don’t think its possible to pack the data in any better at this point.
>>>>>>> 
>>>>>>> Cheers,
>>>>>>> Pete
>>>>>>> 
>>>>>>> <mcsymbol-packing.patch>
>>>>>> 
>>> 
>>> 
>>> _______________________________________________
>>> llvm-commits mailing list
>>> llvm-commits at cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>> 
>>