Improvement suggestions for Epiphany compiler

[mikebell]

[aolofsson]

mikebell,

I tend to agree with all three of your suggestions! If you want to go ahead and submit compiler issue request (one each) that would help out a lot!

https://github.com/adapteva/epiphany-sdk/issues

(if you don't have time, then I will grab the text out of this post and submit issues...)

Andreas

[mikebell]

I've raised issues for 2 and 3 (and given a proposed patch that works-for-me™ for issue 2).

It turns out raising that number of registers is harder than I expected, and is really a core gcc issue, not an epiphany specific one. So I haven't raised an issue for that right now.

Mike

[mikebell]

On further investigation I found it didn't seem too hard to get up to 60 registers in use in an asm block (which is really only a bit more than 30 because of the double counting for read/write regs).

I've raised an issue with a link to a commit that appears to work for me. Again, more testing by someone with more experience would be nice!

Mike

[Gravis]

Reduce the amount of instructions used for stack manipulation!

Upon analysis of disassembled object code I found that between 10% and 20% of instructions are just managing the stack when calling/leaving a function. There are multiple ways to do this, from changing register use rules to having dedicated functions to manage the stack.

[Gravis]

I'm not sure how to command GCC to do this but if you could mark functions or specific variables to use low index registers so that the 16-bit instructions could be used instead of 32-bit ones, that could save a lot of space.

better yet, having a gcc flag to aggressively try and save space by using 16-bit instructions as much as possible would be good.