julia> @trace_compile rand(2,2) * rand(2,2)
#=   13.6 ms =# precompile(Tuple{Core.GeneratedFunctionStub, UInt64, Method, Any, Vararg{Any}}) # recompile
#=   56.2 ms =# precompile(Tuple{typeof(Base.rand), Int64, Int64})
#=    2.9 ms =# precompile(Tuple{typeof(Base.:(*)), Array{Float64, 2}, Array{Float64, 2}})
2×2 Matrix{Float64}:
 0.740604  0.959697
 0.938691  0.937117

julia> @trace_compile rand(2,2) * rand(2,2)
2×2 Matrix{Float64}:
 0.1135    0.162588
 0.463798  0.891144

julia> @time rand(2,2) * rand(2,2)
  0.090083 seconds (174.88 k allocations: 7.729 MiB, 99.95% compilation time)
2×2 Matrix{Float64}:
 0.402414  0.39624
 0.287094  0.210326

julia> @time rand(2,2) * rand(2,2)
  0.000014 seconds (13 allocations: 528 bytes)
2×2 Matrix{Float64}:
 0.1135    0.162588
 0.463798  0.891144

julia> @trace_compile rand(2,2) * rand(2,2)
2×2 Matrix{Float64}:
 0.686422  0.833379
 1.08226   1.23549

julia> @time rand(2,2) * rand(2,2)
  0.000005 seconds (6 allocations: 336 bytes)
2×2 Matrix{Float64}:
 0.183913  0.224988
 0.362542  0.366543

julia> @trace_compile rand(2,2) * rand(2,2);

julia>