Combine four insns

[Steven Bosscher]

On Tue, Aug 10, 2010 at 6:13 PM, Andi Kleen <andi@firstfloor.org> wrote:
> Steven Bosscher <stevenb.gcc@gmail.com> writes:
>
>> On Tue, Aug 10, 2010 at 4:39 PM, Richard Guenther
>> <richard.guenther@gmail.com> wrote:
>>> You could enable the heuristic with optimize < 3 && !optimize_size
>>> (thus keep combining everything at -O3 and -Os).
>>
>> Better s/optimize_size/optimize_bb_for_size(BLOCK_FOR_INSN (i0))/
>
> That would mean that a -O2 build where all BBs are cold for some
> reason would be 1% slower, right?

It's not 1% anymore with the heuristic to only do leaves with 4 insns.
Before that (from Bernd's numbers):

$ grep Trying.four log |wc -l
307743

and after:

$ grep Trying.four log2 |wc -l
187120

So only ~60% of the attempts and probably also less time simplifying.
Slowdown should be less than 0.5% after that.


> To be honest I didn't fully understand why it's ok for -Os
> to be 1% slower. A lot of people use -Os.

Yes, and they expect the smallest code possible. This patch does seem
to help for that.

Ciao!
Steven