Update the spelling of the return register and the return length in the compiler for asm blocks

[mohammadfawaz]

Simply changing rv to ret and rl to retl as per the specs

This:

script;

pub fn return_value() -> u64 {
    asm() {
       ret
    }
}

pub fn return_length() -> u64 {
    asm() {
       retl
    }
}

fn main() {
    let x = return_value();
    let y = return_length();
}

now compiles to:

.program:
ji   i4
noop
DATA_SECTION_OFFSET[0..32]
DATA_SECTION_OFFSET[32..64]
lw   $ds $is 1
add  $$ds $$ds $is
move $r0 $ret                 ; return value from inline asm
move $r0 $retl                ; return value from inline asm
ret  $zero                    ; fn main returns unit
.data:

as expected.

[mohammadfawaz]

@nfurfaro should I add tests for these in the sway/test directory, or will your tests in FuelLabs/sway-lib-std#61 have enough coverage?

[mohammadfawaz]

Also I noticed that, unless the asm block is exercised from main(), syntax errors do not matter. I assume this is due to the fact that we only check asm blocks in codegen.
Looks like @otrho already has an issue on this: #801

[nfurfaro]

@mohammadfawaz I think if the other reserved registers are tested in the sway repo we should test these there as well, butmy guess is they're not. I will definitely test the wrapper functions I'm adding which use ret and retl.

[nfurfaro]

looks good.

[nfurfaro]

LG.