Hoist data pointer loads from array allocations

[pchintalapudi]

When arrays are indexed into, the data pointer is loaded at the indexing site. Typically GVN moves this data pointer load out of loops, but we can do this more eagerly for 2D/3D array allocations and 1D array allocations that do not escape, enabling more of the optimization pipeline to come into play (e.g. loop vectorization).

This PR depends on #43487 for the initial array identification routine as well as the ArrayOpt pass, and therefore #43057 for the escape analysis improvements.

Example:

function f(d1, d2, d3)
           s = 0
           a = zeros(Int, d1, d2, d3)
           for i in eachindex(a)
               s += a[i]
           end
           s
       end

#43487 :
Godbolt: https://godbolt.org/z/9sr36nsvq
Benchmark:

julia> @benchmark f(100,100,100)
BenchmarkTools.Trial: 3347 samples with 1 evaluation.
 Range (min … max):  975.691 μs …   7.981 ms  ┊ GC (min … max):  0.00% …  0.00%
 Time  (median):       1.015 ms               ┊ GC (median):     0.00%
 Time  (mean ± σ):     1.488 ms ± 836.460 μs  ┊ GC (mean ± σ):  10.71% ± 16.41%

  █▆▃                                 ▂▃▁         ▃▃         ▃▃ ▁
  ███▆▃█▄▄▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▄▄▁▁▃▁▁▁▁▃███▅▃▆▇▃▁▁▁▇██▆▅▃▇▇▃▁▁▄██ █
  976 μs        Histogram: log(frequency) by time       3.33 ms <

 Memory estimate: 7.63 MiB, allocs estimate: 2.

PR:
Godbolt: https://godbolt.org/z/8qr8rYv14
Benchmark:

julia> @benchmark f(100,100,100)
BenchmarkTools.Trial: 4292 samples with 1 evaluation.
 Range (min … max):  688.914 μs …   6.848 ms  ┊ GC (min … max):  0.00% … 63.87%
 Time  (median):     723.949 μs               ┊ GC (median):     0.00%
 Time  (mean ± σ):     1.159 ms ± 764.938 μs  ┊ GC (mean ± σ):  10.78% ± 17.55%

  █▆▄   ▁                          ▃▂                ▃▂    ▃▃▁  ▁
  ███▆▄▆█▆▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▄▄▄▁▄████▅▃▇█▇▄▃▁▄▁▁▃▁▃▇████▅▆████ █
  689 μs        Histogram: log(frequency) by time       2.86 ms <

 Memory estimate: 7.63 MiB, allocs estimate: 2.

[pchintalapudi]

Since my branches are part of a fork, I've created a PR comparing this one and the array length propagation PR immediately before it here: pchintalapudi#3

[vchuravy]

Can you add some unit-test specifically for the new llvm-array-opt pass?

[vchuravy]

I would prefer this MD to have a julia prefix.

[vchuravy]

Comment is outdated now? Should instead explain why metadata is used