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interesting list, I might add a few (minor) info

- favor 8 bit variables/constants over 16 bit (or larger!) ones
- unsigned are faster than signed
- use == , != , < , >= wherever possible, as <= and > are slower

when needing to if/else if/else among = or < or > do this:

if (a==SOMEVAL) {
// code to run when EQUAL
} else if (a<SOMEVAL) {
// code to run when LESS THAN
} else {
// code to run when MORE THAN
}

(if the a<SOMEVAL case is the more frequent outcome you can put that first and leave the a==SOMEVAL as second)

Thanks for making this!

What about bitshift rather than multplication/division?

I've read in various places the compiler will optimise this itself in certain circumstances but haven't actually checked, I just do bitshift whenever I can.

[del]

badcomputer wrote

What about bitshift rather than multplication/division?

as toxa said, multiplications/divisions will likely be automatically optimized as long as it's by/divided by a constant so if you write

a=b*4;

it's fine - but if you instead write

a=b*c;

even if c is 4, there won't be any optimization.

(it might have been obvious but once I had a similar discussion with a game developer about the fact he was multiplying with a variable map_width whose value could be either 32 or 64 and was suggesting that the compiler would optimize that... no, it doesn't).

Is it worth using --opt-code-speed with SDCC? Or any other compiler options that might help?

badcomputer wrote

Is it worth using --opt-code-speed with SDCC? Or any other compiler options that might help?

I always turn that on.
I keep meaning to do the experiment of what differences it made. I thought it caused more inlining (including of functions) but Toxa said at some point that functions are never automatically inlined, so not sure.

[del]

toxa wrote

badcomputer wrote

Is it worth using --opt-code-speed with SDCC? Or any other compiler options that might help?

I never use that, --max-allocs-per-node with some large value produce better results.

I haven't tried this, any advice about which value to use?

[del]

toxa wrote

kusfo wrote

I haven't tried this, any advice about which value to use?

50000 and above. but that may slow down the compiling process.

Thanks! I'll test it, I can have it enabled only for the release process

I compile SMSlib for release using

--max-allocs-per-node 100000

but it really takes *a lot* of time and it hardly is much different from what I would get without it. But I thought it's worth for a release build.

[del]

toxa wrote

sverx wrote

I compile SMSlib for release using

SMSlib has very little and very specific C code and thus not much opportunities to optimize anything

True, and that's why I said
>> it hardly is much different from what I would get without it

still, I don't get exactly the same output without it, since there are still parts which aren't written in inline asm.

Author	Message
toxa Joined: 09 Aug 2021 Posts: 139	SDCC: best practices for designing the game in C Posted: Wed Apr 17, 2024 11:48 am Last edited by toxa on Yesterday at 7:14 pm; edited 1 time in total
toxa Joined: 09 Aug 2021 Posts: 139	[del]

sverx Joined: 05 Sep 2013 Posts: 3855 Location: Stockholm, Sweden	Posted: Wed Apr 17, 2024 1:54 pm
	interesting list, I might add a few (minor) info - favor 8 bit variables/constants over 16 bit (or larger!) ones - unsigned are faster than signed - use == , != , < , >= wherever possible, as <= and > are slower when needing to if/else if/else among = or < or > do this: if (a==SOMEVAL) { // code to run when EQUAL } else if (a<SOMEVAL) { // code to run when LESS THAN } else { // code to run when MORE THAN } (if the a<SOMEVAL case is the more frequent outcome you can put that first and leave the a==SOMEVAL as second)

badcomputer Joined: 19 Oct 2023 Posts: 160	Posted: Wed Apr 17, 2024 3:18 pm
badcomputer Joined: 19 Oct 2023 Posts: 160	Thanks for making this! What about bitshift rather than multplication/division? I've read in various places the compiler will optimise this itself in certain circumstances but haven't actually checked, I just do bitshift whenever I can.

toxa Joined: 09 Aug 2021 Posts: 139	Posted: Wed Apr 17, 2024 3:36 pm Last edited by toxa on Yesterday at 7:14 pm; edited 1 time in total
toxa Joined: 09 Aug 2021 Posts: 139	[del]

sverx Joined: 05 Sep 2013 Posts: 3855 Location: Stockholm, Sweden	Posted: Wed Apr 17, 2024 4:36 pm
	badcomputer wrote What about bitshift rather than multplication/division? as toxa said, multiplications/divisions will likely be automatically optimized as long as it's by/divided by a constant so if you write a=b4; it's fine - but if you instead write a=bc; even if c is 4, there won't be any optimization. (it might have been obvious but once I had a similar discussion with a game developer about the fact he was multiplying with a variable map_width whose value could be either 32 or 64 and was suggesting that the compiler would optimize that... no, it doesn't).

badcomputer Joined: 19 Oct 2023 Posts: 160	Posted: Wed Apr 17, 2024 6:32 pm
badcomputer Joined: 19 Oct 2023 Posts: 160	Is it worth using --opt-code-speed with SDCC? Or any other compiler options that might help?

willbritton Joined: 06 Mar 2022 Posts: 679 Location: London, UK	Posted: Wed Apr 17, 2024 6:49 pm
	badcomputer wrote Is it worth using --opt-code-speed with SDCC? Or any other compiler options that might help? I always turn that on. I keep meaning to do the experiment of what differences it made. I thought it caused more inlining (including of functions) but Toxa said at some point that functions are never automatically inlined, so not sure.

toxa Joined: 09 Aug 2021 Posts: 139	Posted: Wed Apr 17, 2024 7:06 pm Last edited by toxa on Yesterday at 7:15 pm; edited 1 time in total
toxa Joined: 09 Aug 2021 Posts: 139	[del]

kusfo Joined: 29 Mar 2012 Posts: 888 Location: Spain	Posted: Thu Apr 18, 2024 7:44 am
kusfo Joined: 29 Mar 2012 Posts: 888 Location: Spain	toxa wrote badcomputer wrote Is it worth using --opt-code-speed with SDCC? Or any other compiler options that might help? I never use that, --max-allocs-per-node with some large value produce better results. I haven't tried this, any advice about which value to use?

toxa Joined: 09 Aug 2021 Posts: 139	Posted: Thu Apr 18, 2024 8:01 am Last edited by toxa on Yesterday at 7:15 pm; edited 1 time in total
toxa Joined: 09 Aug 2021 Posts: 139	[del]

kusfo Joined: 29 Mar 2012 Posts: 888 Location: Spain	Posted: Thu Apr 18, 2024 8:19 am
kusfo Joined: 29 Mar 2012 Posts: 888 Location: Spain	toxa wrote kusfo wrote I haven't tried this, any advice about which value to use? 50000 and above. but that may slow down the compiling process. Thanks! I'll test it, I can have it enabled only for the release process

sverx Joined: 05 Sep 2013 Posts: 3855 Location: Stockholm, Sweden	Posted: Thu Apr 18, 2024 9:42 am
	I compile SMSlib for release using --max-allocs-per-node 100000 but it really takes a lot of time and it hardly is much different from what I would get without it. But I thought it's worth for a release build.

toxa Joined: 09 Aug 2021 Posts: 139	Posted: Thu Apr 18, 2024 9:43 pm Last edited by toxa on Yesterday at 7:15 pm; edited 1 time in total
toxa Joined: 09 Aug 2021 Posts: 139	[del]

sverx Joined: 05 Sep 2013 Posts: 3855 Location: Stockholm, Sweden	Posted: Fri Apr 19, 2024 7:43 am
	toxa wrote sverx wrote I compile SMSlib for release using SMSlib has very little and very specific C code and thus not much opportunities to optimize anything True, and that's why I said >> it hardly is much different from what I would get without it still, I don't get exactly the same output without it, since there are still parts which aren't written in inline asm.

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