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Revision a121721f975fc4105ed24ebd0ad1020d08d07a38 authored by Shuhei Kadowaki on 01 November 2021, 10:49:07 UTC, committed by GitHub on 01 November 2021, 10:49:07 UTC 
inference: form `PartialStruct` for extra type information propagation (#42831)
 
* inference: form `PartialStruct` for extra type information propagation

This commit forms `PartialStruct` whenever there is any type-level
refinement available about a field, even if it's not "constant" information.

In Julia "definitions" are allowed to be abstract whereas "usages"
(i.e. callsites) are often concrete. The basic idea is to allow inference
to make more use of such precise callsite type information by encoding it
as `PartialStruct`.

This may increase optimization possibilities of "unidiomatic" Julia code,
which may contain poorly-typed definitions, like this very contrived example:
```julia
struct Problem
    n; s; c; t
end

function main(args...)
    prob = Problem(args...)
    s = 0
    for i in 1:prob.n
        m = mod(i, 3)
        s += m == 0 ? sin(prob.s) : m == 1 ? cos(prob.c) : tan(prob.t)
    end
    return prob, s
end

main(10000, 1, 2, 3)
```

One of the obvious limitation is that this extra type information can be
propagated inter-procedurally only as a const-propagation.
I'm not sure this kind of "just a type-level" refinement can often make
constant-prop' successful (i.e. shape-up a method body and allow it to
be inlined, encoding the extra type information into the generated code),
thus I didn't not modify any part of const-prop' heuristics.

So the improvements from this change might not be very useful for general
inter-procedural analysis currently, but they should definitely improve the
accuracy of local analysis and very simple inter-procedural analysis.
1 parent 6c274ed
Raw File
refvalue.jl 
# This file is a part of Julia. License is MIT: https://julialang.org/license

### Methods for a Ref object that can store a single value of any type

mutable struct RefValue{T} <: Ref{T}
    x::T
    RefValue{T}() where {T} = new()
    RefValue{T}(x) where {T} = new(x)
end
RefValue(x::T) where {T} = RefValue{T}(x)
"""
    isassigned(ref::RefValue) -> Bool

Test whether the given [`Ref`](@ref) is associated with a value.
This is always true for a [`Ref`](@ref) of a bitstype object.
Return `false` if the reference is undefined.

# Examples
```jldoctest
julia> ref = Ref{Function}()
Base.RefValue{Function}(#undef)

julia> isassigned(ref)
false

julia> ref[] = (foobar(x) = x)
foobar (generic function with 1 method)

julia> isassigned(ref)
true

julia> isassigned(Ref{Int}())
true
```
"""
isassigned(x::RefValue) = isdefined(x, :x)

function unsafe_convert(P::Union{Type{Ptr{T}},Type{Ptr{Cvoid}}}, b::RefValue{T})::P where T
    if allocatedinline(T)
        p = pointer_from_objref(b)
    elseif isconcretetype(T) && ismutabletype(T)
        p = pointer_from_objref(b.x)
    else
        # If the slot is not leaf type, it could be either immutable or not.
        # If it is actually an immutable, then we can't take it's pointer directly
        # Instead, explicitly load the pointer from the `RefValue`,
        # which also ensures this returns same pointer as the one rooted in the `RefValue` object.
        p = pointerref(Ptr{Ptr{Cvoid}}(pointer_from_objref(b)), 1, Core.sizeof(Ptr{Cvoid}))
    end
    return p
end
function unsafe_convert(::Type{Ptr{Any}}, b::RefValue{Any})::Ptr{Any}
    return pointer_from_objref(b)
end

getindex(b::RefValue) = b.x
setindex!(b::RefValue, x) = (b.x = x; b)
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