Thumb2 code size improvements

[Yao Qi]

Andrew Stubbs wrote:
> On 06/09/10 07:16, Yao Qi wrote:
>> I've put some ideas in this wiki page,
>> https://wiki.linaro.org/Internal/People/YaoQi/Thumb2Optimize
> 
> We probably shouldn't post Internal links to this public list. Is there 
> any reason this can't be done in the open?
I've moved this page to a public place
https://wiki.linaro.org/YaoQi/Sandbox/Thumb2SizeOptimize

> Now for the page content ....
> 
> I think you should make clear that we're after _size_ optimizations in 
> this case, if just for readability's sake.
> 
> 1. This example (regardless of correctness) gains no size improvement.
> 
OK, I should remove this one.

> 2. This code is clearly an inlined memset. It might be that a branch 
> instruction with constants and such is not (much) smaller. We should 
> investigate what GCC does for different size writes.
> 
Yeah, I agree that we should investigate how gcc does for different size.

> 3. This sounds like a nightmare for register allocation, but if you 
> could make it happen then great :)
> 
> ....
> 
> 6. Is that an EEMBC function? We can't change those in the source. Are 
> you proposing a -fwhole-program optimization? (Of course, enabling 
> inlining at -Os for trivial functions like this might work without 
> -fwhole-program or LTO, if it's in the same TU.)
> 
Yes, that is an EEMBC function.  Of course, we can't change source code.
   It is not related to thumb2 code size optimization.  I've moved it to
another section.

> Other ideas:
> 
> * https://bugs.launchpad.net/gcc-linaro/+bug/625233

Add it in this wiki page.

> * Investigate reduced alignment constraints?

Any details on this?