Commits on Oct 11, 2024

1. optimizer: allow EA-powered finalizer inlining …

   E.g. this allows `finalizer` inlining in the following case:
   ```julia
   mutable struct ForeignBuffer{T}
       const ptr::Ptr{T}
   end
   const foreign_buffer_finalized = Ref(false)
   function foreign_alloc(::Type{T}, length) where T
       ptr = Libc.malloc(sizeof(T) * length)
       ptr = Base.unsafe_convert(Ptr{T}, ptr)
       obj = ForeignBuffer{T}(ptr)
       return finalizer(obj) do obj
           Base.@assume_effects :notaskstate :nothrow
           foreign_buffer_finalized[] = true
           Libc.free(obj.ptr)
       end
   end
   function f_EA_finalizer(N::Int)
       workspace = foreign_alloc(Float64, N)
       GC.@preserve workspace begin
           (;ptr) = workspace
           Base.@assume_effects :nothrow @noinline println(devnull, "ptr = ", ptr)
       end
   end
   ```
   ```julia
   julia> @code_typed f_EA_finalizer(42)
   CodeInfo(
   1 ── %1  = Base.mul_int(8, N)::Int64
   │    %2  = Core.lshr_int(%1, 63)::Int64
   │    %3  = Core.trunc_int(Core.UInt8, %2)::UInt8
   │    %4  = Core.eq_int(%3, 0x01)::Bool
   └───       goto #3 if not %4
   2 ──       invoke Core.throw_inexacterror(:convert::Symbol, UInt64::Type, %1::Int64)::Union{}
   └───       unreachable
   3 ──       goto #4
   4 ── %9  = Core.bitcast(Core.UInt64, %1)::UInt64
   └───       goto #5
   5 ──       goto #6
   6 ──       goto #7
   7 ──       goto #8
   8 ── %14 = $(Expr(:foreigncall, :(:malloc), Ptr{Nothing}, svec(UInt64), 0, :(:ccall), :(%9), :(%9)))::Ptr{Nothing}
   └───       goto #9
   9 ── %16 = Base.bitcast(Ptr{Float64}, %14)::Ptr{Float64}
   │    %17 = %new(ForeignBuffer{Float64}, %16)::ForeignBuffer{Float64}
   └───       goto #10
   10 ─ %19 = $(Expr(:gc_preserve_begin, :(%17)))
   │    %20 = Base.getfield(%17, :ptr)::Ptr{Float64}
   │          invoke Main.println(Main.devnull::Base.DevNull, "ptr = "::String, %20::Ptr{Float64})::Nothing
   │          $(Expr(:gc_preserve_end, :(%19)))
   │    %23 = Main.foreign_buffer_finalized::Base.RefValue{Bool}
   │          Base.setfield!(%23, :x, true)::Bool
   │    %25 = Base.getfield(%17, :ptr)::Ptr{Float64}
   │    %26 = Base.bitcast(Ptr{Nothing}, %25)::Ptr{Nothing}
   │          $(Expr(:foreigncall, :(:free), Nothing, svec(Ptr{Nothing}), 0, :(:ccall), :(%26), :(%25)))::Nothing
   └───       return nothing
   ) => Nothing
   ```
   
   However, this is still a WIP. Before merging, I want to improve EA's
   precision a bit and at least fix the test case that is currently marked as
   `broken`. I also need to check its impact on compiler performance.
   
   Additionally, I believe this feature is not yet practical.
   In particular, there is still significant room for improvement in the
   following areas:
   - EA's interprocedural capabilities: currently EA is performed ad-hoc
     for limited frames because of latency reasons, which significantly
     reduces its precision in the presence of interprocedural calls.
   - Relaxing the `:nothrow` check for finalizer inlining: the current
     algorithm requires `:nothrow`-ness on all paths from the allocation of
     the mutable struct to its last use, which is not practical for
     real-world cases. Even when `:nothrow` cannot be guaranteed, auxiliary
     optimizations such as inserting a `finalize` call after the last use
     might still be possible.

   

   aviatesk committed Oct 11, 2024
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2. fix EA regression

   

   aviatesk committed Oct 11, 2024
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3. better EAUtils.jl

   

   aviatesk committed Oct 11, 2024
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4. wip: fix EA regression, better approach

   

   aviatesk committed Oct 11, 2024
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