Can you change the base branch from which you made changes specific for this PR (for easier review)?

At a glance, it looks like you miss some cases when array allocations are "unsafe", e.g.:

function foo()
    a = Vector{Int}(undef, -10) # shouldn't be eliminated, otherwise it changes the error semantics
    nothing
end

Given that this essentially needs some shape information, I guess we can implement this at Julia level relatively easier?
But your work on LLVM level escape analysis (and shape analysis?) may enable further optimizations though.

Since my branches are part of a fork, I've created a PR comparing this one and the branch elimination PR immediately before it here: pchintalapudi#1

Converting to draft because #43487, #43547, and #43384 are still under review.