RFA: Darwin x86 alignment

[Dale Johannesen]

On Jul 21, 2005, at 5:00 PM, Richard Henderson wrote:

> On Thu, Jul 21, 2005 at 04:56:01PM -0700, Dale Johannesen wrote:
>> - Have flags work as now:  -malign-double makes both 8,
>> -mno-align-double
>>   makes both 4.  Problem with that is the default is neither of these,
>> and
>>   this doesn't fit neatly into gcc's model of two-valued flags; it's
>> also a bit
>>   tricky to implement for the same reason.
>
> Nah, you just remove it from target_flags, and control the two
> new variables from ix86_handle_option.

OK.  Think that's the better approach?

> Why do you want to make these sort of arbitrary changes to your
> ABI?  I can't see what you win...

The compiler people are not driving this.

Of course, 4-byte alignment subjects you to a penalty for misaligned
loads and stores, and 8-byte alignment subjects you to a size penalty
for extra holes.   People have been making measurements about the
issue and this is what they've come up with; I don't know details.
What I wrote isn't necessarily the final change, either.