help bounds checking to be eliminated for getindex(::Memory, ::Int)

[nsajko]

Second try for PR #58741.

This moves the getindex(::Memory, ::Int) bounds check to Julia, which is how it's already done for getindex(::Array, ::Int), so I guess it's correct.

Also deduplicate the bounds checking code while at it.

[nsajko]

Reproducer:

function g(a::AbstractArray{Float32}, i::Int)
    @inline let
        if checkbounds(Bool, a, i)
            a[i]
        else
            Float32(0)
        end
    end
end

code_llvm(g, Tuple{Memory{Float32}, Int}; debuginfo=:none)  # there should be no more bounds checking after this PR

[gbaraldi]

@nanosoldier runbenchmarks(ALL, vs=":master")

[giordano]

At a quick glance, this seems to help quite a bit for JuliaArrays/FixedSizeArrays.jl#142, but not fully close the gap.

[oscardssmith]

#58768 should also hopefully help with this (once the codegen gets updated to work with this)

[nanosoldier]

Your benchmark job has completed - possible performance regressions were detected. A full report can be found here.

[oscardssmith]

benchmarks look totally meaningless (we seem to be missing any Memory benchmarks). That said, lgtm.

[nsajko]

I tried to reproduce one regression and one perf improvement locally, both turned out to be noise.

[nsajko]

Merge? I'd like to rebase #58755 on top of this.