tier 3 target and broken

[stappersg]

This issue is for creating awareness for rust-lang/rust#126349

avr-unknown-gnu-atmega328 (ran out of registers during register allocation)

That rust lang request got my attention, but have no resources available for any follow-up. Hence this issue.

I hope some one accepts the challenge.

Any way: Happy Hacking

[adicarlo]

BTW, I'm still a bit newbie when it comes to rust-avr, but I found that core will build debug mode if you add to Cargo.toml:

[profile.dev]
opt-level = 1

Reviewing rust-lang/rust#126349 it seems like we might have a few ways to go here, maybe from easiest to hardest:

1. hack on rustc guts so raise opt-level 0 to 1 in all cases ?
2. track down what is causing the register allocation problem and fix it in the source
3. accelerate the shift away from GCC and towards LLVM

I'm happy to pitch in here but I would probably need a bit of guidance on which approach to take...

[Rahix]

Slightly off-topic for this issue, but @adicarlo, you should be setting even more compiler tunes to get AVR programs to build properly:

avr-hal/Cargo.toml

Lines 1 to 11 in 65b304e

	[profile.dev]
	panic = "abort"
	lto = true
	opt-level = "s"
	[profile.release]
	panic = "abort"
	codegen-units = 1
	debug = true
	lto = true
	opt-level = "s"

[adicarlo]

@Rahix i see that, from over at https://github.com/Rahix/avr-hal-template/blob/main/Cargo.toml#L55

You say "needed to build" but I'm able to build without all that -- I assume you're saying it wouldn't work (or work well) on actual hardware w/o those settings from the template?

[stappersg]

On Thu, Aug 15, 2024 at 04:08:14PM -0700, Adam Di Carlo wrote: you're saying it wouldn't work (or work well) on actual hardware

Yes. Experiment for those who don't want to get their feet wet on true hardware: - Build with recommend settings - Build with "Hey, it compiles" settings - Compare size of the executables

[aykevl]

I suspect this is the same register allocation bug: llvm/llvm-project#104032

[adicarlo]

@aykevl that's very promising! You boiled out a simple/general test case. Looks like its getting some action too...