AllocCheck.jl is a Julia package that statically checks if a function call may allocate, analyzing the generated LLVM IR of it and it's callees using LLVM.jl and GPUCompiler.jl
AllocCheck operates on functions, trying to statically determine wether or not a function may allocate memory, and if so, where that allocation appears. This is different from measuring allocations using, e.g., @time or @allocated, which measures the allocations that did happen during the execution of a function.
The primary entry point to check allocations is the macro @check_allocs which is used to annotate a function definition that you'd like to enforce allocation checks for:
julia> using AllocCheck
julia> @check_allocs multiply(x,y) = x * y
multiply (generic function with 1 method)
julia> multiply(1.5, 2.5) # call automatically checked for allocations
3.75
julia> multiply(rand(3,3), rand(3,3)) # result matrix requires an allocation
ERROR: @check_alloc function encountered 1 errors (1 allocations / 0 dynamic dispatches).The multiply(::Float64, ::Float64) call happened without error, indicating that the function was proven not to allocate. On the other hand, the multiply(::Matrix{Float64}, ::Matrix{Float64}) call raised an AllocCheckFailure due to one internal allocation.
The errors field can be used to inspect the individual errors:
julia> try multiply(rand(3,3), rand(3,3)) catch err err.errors[1] end
Allocation of Matrix{Float64} in ./boot.jl:477
| Array{T,2}(::UndefInitializer, m::Int, n::Int) where {T} =
Stacktrace:
[1] Array
@ ./boot.jl:477 [inlined]
[2] Array
@ ./boot.jl:485 [inlined]
[3] similar
@ ./array.jl:418 [inlined]
[4] *(A::Matrix{Float64}, B::Matrix{Float64})
@ LinearAlgebra ~/.julia/juliaup/julia-1.10.0-rc1+0.x64.linux.gnu/share/julia/stdlib/v1.10/LinearAlgebra/src/matmul.jl:113
[5] var"##multiply#235"(x::Matrix{Float64}, y::Matrix{Float64})
@ Main ./REPL[13]:1Some functions that we do not expect may allocate memory, like sin, actually may:
julia> @allocated try sin(Inf) catch end
48The reason for this is that sin needs to allocate if it throws an error.
By default, @check_allocs ignores all such allocations and assumes that no exceptions are thrown. If you care about detecting these allocations anyway, you can use ignore_throw=false:
julia> @check_allocs mysin1(x) = sin(x)
julia> @check_allocs ignore_throw=false mysin2(x) = sin(x)
julia> mysin1(1.5)
0.9974949866040544
julia> mysin2(1.5)
ERROR: @check_alloc function encountered 2 errors (1 allocations / 1 dynamic dispatches).Every call into a @check_allocs function behaves like a dynamic dispatch. This means that it can trigger compilation dynamically (involving lots of allocation), and even when the function has already been compiled, a small amount of allocation is still expected on function entry.
For most applications, the solution is to use @check_allocs to wrap your top-level entry point or your main application loop, in which case those applications are only incurred once. @check_allocs will guarantee that no dynamic compilation or allocation occurs once your function has started running.