Add Base.isprecompilable (JuliaLang#58805) (#246)

Alternative to JuliaLang#58146.

We want to compile a subset of the possible specializations of a
function. To this end, we have a number of manually written `precompile`
statements. Creating this list is, unfortunately, error-prone, and the
list is also liable to going stale. Thus we'd like to validate each
`precompile` statement in the list.

The simple answer is, of course, to actually run the `precompile`s, and
we naturally do so, but this takes time.

We would like a relatively quick way to check the validity of a
`precompile` statement.
This is a dev-loop optimization, to allow us to check "is-precompilable"
in unit tests.

We can't use `hasmethod` as it has both false positives (too loose):
```julia
julia> hasmethod(sum, (AbstractVector,))
true

julia> precompile(sum, (AbstractVector,))
false

julia> Base.isprecompilable(sum, (AbstractVector,)) # <- this PR
false
```
and also false negatives (too strict):
```julia
julia> bar(@nospecialize(x::AbstractVector{Int})) = 42
bar (generic function with 1 method)

julia> hasmethod(bar, (AbstractVector,))
false

julia> precompile(bar, (AbstractVector,))
true

julia> Base.isprecompilable(bar, (AbstractVector,)) # <- this PR
true
```
We can't use `hasmethod && isconcretetype` as it has false negatives
(too strict):
```julia
julia> has_concrete_method(f, argtypes) = all(isconcretetype, argtypes) && hasmethod(f, argtypes)
has_concrete_method (generic function with 1 method)

julia> has_concrete_method(bar, (AbstractVector,))
false

julia> has_concrete_method(convert, (Type{Int}, Int32))
false

julia> precompile(convert, (Type{Int}, Int32))
true

julia> Base.isprecompilable(convert, (Type{Int}, Int32))  # <- this PR
true
```
`Base.isprecompilable` is essentially `precompile` without the actual
compilation.

Co-authored-by: Kiran Pamnany <[email protected]>

Author: NHDaly

base/loading.jl

@@ -3209,6 +3209,20 @@ macro __DIR__()
     return isempty(_dirname) ? pwd() : abspath(_dirname)
 end
 
+"""
+    isprecompilable(f, argtypes::Tuple{Vararg{Any}})
+
+Check, as far as is possible without actually compiling, if the given
+function `f` can be compiled for the argument tuple (of types) `argtypes`.
+"""
+function isprecompilable(@nospecialize(f), @nospecialize(argtypes::Tuple))
+    isprecompilable(Tuple{Core.Typeof(f), argtypes...})
+end
+
+function isprecompilable(@nospecialize(argt::Type))
+    ccall(:jl_is_compilable, Int32, (Any,), argt) != 0
+end
+
 """
     precompile(f, argtypes::Tuple{Vararg{Any}})
 

src/gf.c

@@ -2929,6 +2929,15 @@ JL_DLLEXPORT void jl_compile_method_instance(jl_method_instance_t *mi, jl_tuplet
     }
 }
 
+JL_DLLEXPORT int jl_is_compilable(jl_tupletype_t *types)
+{
+    size_t world = jl_atomic_load_acquire(&jl_world_counter);
+    size_t min_valid = 0;
+    size_t max_valid = ~(size_t)0;
+    jl_method_instance_t *mi = jl_get_compile_hint_specialization(types, world, &min_valid, &max_valid, 1);
+    return mi == NULL ? 0 : 1;
+}
+
 JL_DLLEXPORT int jl_compile_hint(jl_tupletype_t *types)
 {
     size_t world = jl_atomic_load_acquire(&jl_world_counter);

src/jl_exported_funcs.inc

@@ -286,6 +286,7 @@
     XX(jl_istopmod) \
     XX(jl_is_binding_deprecated) \
     XX(jl_is_char_signed) \
+    XX(jl_is_compilable) \
     XX(jl_is_const) \
     XX(jl_is_debugbuild) \
     XX(jl_is_foreign_type) \