inlining: optimize and_int(x, true) and or_int(x, false)

[aviatesk]

We need an additional inlining pass to optimize cases like and_int(x, true) and or_int(x, false) to x.

[vtjnash]

It is not entirely true, since it actually is equivalent to the type-assert call x::Bool. Is there a reason we need this in Julia, rather than letting it occur in LLVM after the IR simplifications?

[aviatesk]

LLVM does not seem to optimize these intrinsic patterns:

julia> code_llvm((Bool,)) do x
           x & true
       end
; Function Signature: var"#10"(Bool)
;  @ REPL[1]:2 within `#10`
define i8 @"julia_#10_2272"(i8 zeroext %"x::Bool") #0 {
top:
; ┌ @ bool.jl:38 within `&`
   %0 = and i8 %"x::Bool", 1
   ret i8 %0
; └
}

And I think simplifications for such low-level intrinsics should be done early on?

[vchuravy]

That's because LLVM doesn't know that the upper seven bits are ignored...

We used to represent bool as i1, but that caused other problems #17225

[vchuravy]

Clang btw still uses i1 for Bool, so it might be worthwhile trying to switch the implementation back.

[oscardssmith]

I think our medium term goal is to switch it back. We just have to first make sure that bools on construction always have valid bit-patterns. I believe the plan for how to do this is to always zero initialize bytes that have store bools.

[giordano]

Relevant issue about switching to i1: #21712