[llvm] r300171 - [APInt] Reorder fields to avoid a hole in the middle of the class

[Craig Topper via llvm-commits]

Would it be sufficient to add a static_assert to APSInt.h?  Can't do it in
APInt.h because the padding is counted in sizeof whether its in the middle
or at the end.

~Craig

On Wed, Apr 12, 2017 at 11:36 PM, Davide Italiano <davide at freebsd.org>
wrote:

> On Wed, Apr 12, 2017 at 9:59 PM, Craig Topper via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
> > Author: ctopper
> > Date: Wed Apr 12 23:59:11 2017
> > New Revision: 300171
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=300171&view=rev
> > Log:
> > [APInt] Reorder fields to avoid a hole in the middle of the class
> >
> > Summary:
> > APInt is currently implemented with an unsigned BitWidth field first and
> then a uint_64/pointer union. Due to the 64-bit size of the union there is
> a hole after the bitwidth.
> >
> > Putting the union first allows the class to be packed. Making it 12
> bytes instead of 16 bytes. An APSInt goes from 20 bytes to 16 bytes.
> >
> > This shows a 4k reduction on the size of the opt binary on my local
> x86-64 build. So this enables some other improvement to the code as well.
> >
>
> As mentioned in the review, can you please try to write an unittest to
> make sure this doesn't break in future?
>
> Thanks,
>
> --
> Davide
>
> "There are no solved problems; there are only problems that are more
> or less solved" -- Henri Poincare
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170413/658202ad/attachment.html>