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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
ntuple.jl 
# This file is a part of Julia. License is MIT: https://julialang.org/license

# `ntuple`, for constructing tuples of a given length

"""
    ntuple(f::Function, n::Integer)

Create a tuple of length `n`, computing each element as `f(i)`,
where `i` is the index of the element.

# Examples
```jldoctest
julia> ntuple(i -> 2*i, 4)
(2, 4, 6, 8)
```
"""
@inline function ntuple(f::F, n::Integer) where F
    # marked inline since this benefits from constant propagation of `n`
    t = n == 0  ? () :
        n == 1  ? (f(1),) :
        n == 2  ? (f(1), f(2)) :
        n == 3  ? (f(1), f(2), f(3)) :
        n == 4  ? (f(1), f(2), f(3), f(4)) :
        n == 5  ? (f(1), f(2), f(3), f(4), f(5)) :
        n == 6  ? (f(1), f(2), f(3), f(4), f(5), f(6)) :
        n == 7  ? (f(1), f(2), f(3), f(4), f(5), f(6), f(7)) :
        n == 8  ? (f(1), f(2), f(3), f(4), f(5), f(6), f(7), f(8)) :
        n == 9  ? (f(1), f(2), f(3), f(4), f(5), f(6), f(7), f(8), f(9)) :
        n == 10 ? (f(1), f(2), f(3), f(4), f(5), f(6), f(7), f(8), f(9), f(10)) :
        _ntuple(f, n)
    return t
end

function _ntuple(f::F, n) where F
    @noinline
    (n >= 0) || throw(ArgumentError(string("tuple length should be ≥ 0, got ", n)))
    ([f(i) for i = 1:n]...,)
end

function ntupleany(f, n)
    @noinline
    (n >= 0) || throw(ArgumentError(string("tuple length should be ≥ 0, got ", n)))
    (Any[f(i) for i = 1:n]...,)
end

# inferrable ntuple (enough for bootstrapping)
ntuple(f, ::Val{0}) = ()
ntuple(f, ::Val{1}) = (@inline; (f(1),))
ntuple(f, ::Val{2}) = (@inline; (f(1), f(2)))
ntuple(f, ::Val{3}) = (@inline; (f(1), f(2), f(3)))

"""
    ntuple(f, ::Val{N})

Create a tuple of length `N`, computing each element as `f(i)`,
where `i` is the index of the element. By taking a `Val(N)`
argument, it is possible that this version of ntuple may
generate more efficient code than the version taking the
length as an integer. But `ntuple(f, N)` is preferable to
`ntuple(f, Val(N))` in cases where `N` cannot be determined
at compile time.

# Examples
```jldoctest
julia> ntuple(i -> 2*i, Val(4))
(2, 4, 6, 8)
```
"""
@inline function ntuple(f::F, ::Val{N}) where {F,N}
    N::Int
    (N >= 0) || throw(ArgumentError(string("tuple length should be ≥ 0, got ", N)))
    if @generated
        quote
            @nexprs $N i -> t_i = f(i)
            @ncall $N tuple t
        end
    else
        Tuple(f(i) for i = 1:N)
    end
end

@inline function fill_to_length(t::Tuple, val, ::Val{_N}) where {_N}
    M = length(t)
    N = _N::Int
    M > N && throw(ArgumentError("input tuple of length $M, requested $N"))
    if @generated
        quote
            (t..., $(fill(:val, (_N::Int) - length(t.parameters))...))
        end
    else
        (t..., fill(val, N-M)...)
    end
end
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