Codegen backend handles compare binops for the unit type

[bjorn3]

rust/src/librustc_codegen_ssa/mir/rvalue.rs

Lines 586 to 592 in c43d03a

	mir::BinOp::Ne | mir::BinOp::Lt | mir::BinOp::Gt |
	mir::BinOp::Eq | mir::BinOp::Le | mir::BinOp::Ge => if is_unit {
	bx.cx().const_bool(match op {
	mir::BinOp::Ne | mir::BinOp::Lt | mir::BinOp::Gt => false,
	mir::BinOp::Eq | mir::BinOp::Le | mir::BinOp::Ge => true,
	_ => unreachable!()
	})

libcore however doesn't use those for the implementations for PartialEq and PartialOrd for the unit type.

rust/src/libcore/cmp.rs

Lines 933 to 939 in c43d03a

	#[stable(feature = "rust1", since = "1.0.0")]
	impl PartialEq for () {
	#[inline]
	fn eq(&self, _other: &()) -> bool { true }
	#[inline]
	fn ne(&self, _other: &()) -> bool { false }
	}

rust/src/libcore/cmp.rs

Lines 980 to 985 in c43d03a

	impl PartialOrd for () {
	#[inline]
	fn partial_cmp(&self, _: &()) -> Option<Ordering> {
	Some(Equal)
	}
	}

This means that the special case in cg_ssa can be removed.

[punitkoura]

Hi @bjorn3 @Centril, I'd like to work on this. Would be a good initial contribution to Rust :)

[punitkoura]

I'm really new to the code base, though. Could you clarify what the cg_ssa means above?

[jonas-schievink]

Could you clarify what the cg_ssa means above?

That's librustc_codegen_ssa, a part of the code generation code in rustc. The code in the first snippet is located there.

[punitkoura]

Thanks for clarifying that! I'll go through the code and post any questions here.

[TheOregonTrail]

Would love to help but don't know where to start. If mentoring is still possible please ping me or send me in the right direction somehow 👍 . @bjorn3 @Centril

[TheOregonTrail]

or maybe @jonas-schievink if your up to the task :)

[jonas-schievink]

@luigisHat I think you just need to look at src/librustc_codegen_ssa/mir/rvalue.rs and remove the check for is_unit that was mentioned. You can check https://rust-lang.github.io/rustc-guide/ for an overview of the compiler and instruction on how to build it and run tests.

[TheOregonTrail]

@jonas-schievink Thanks seems to be a little simpler then I thought once I dug into the docs. Will do hope your having a good one 👍 .