JuliaLang / julia / #37547
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Merge pull request #41931 from JuliaLang/avi/noinfer

* introduce `@nospecializeinfer` macro to tell the compiler to avoid excess inference

This commit introduces a new compiler annotation called `@nospecializeinfer`,
which allows us to request the compiler to avoid excessive inference.

\## `@nospecialize` mechanism

T discuss `@nospecializeinfer`, let's first understand the behavior of
`@nospecialize`.

Its docstring says that

> This is only a hint for the compiler to avoid excess code generation.

, and it works by suppressing dispatches with complex runtime
occurrences of the annotated arguments. This could be understood with
the example below:
```julia
julia> function call_func_itr(func, itr)
           local r = 0
           r += func(itr[1])
           r += func(itr[2])
           r += func(itr[3])
           r
       end;

julia> _isa = isa; # just for the sake of explanation, global variable to prevent inlining

julia> func_specialize(a) = _isa(a, Function);

julia> func_nospecialize(@nospecialize a) = _isa(a, Function);

julia> dispatchonly = Any[sin, muladd, nothing]; # untyped container can cause excessive runtime dispatch

julia> @code_typed call_func_itr(func_specialize, dispatchonly)
CodeInfo(
1 ─ %1  = π (0, Int64)
│   %2  = Base.arrayref(true, itr, 1)::Any
│   %3  = (func)(%2)::Any
│   %4  = (%1 + %3)::Any
│   %5  = Base.arrayref(true, itr, 2)::Any
│   %6  = (func)(%5)::Any
│   %7  = (%4 + %6)::Any
│   %8  = Base.arrayref(true, itr, 3)::Any
│   %9  = (func)(%8)::Any
│   %10 = (%7 + %9)::Any
└──       return %10
) => Any

julia> @code_typed call_func_itr(func_nospecialize, dispatchonly)
CodeInfo(
1 ─ %1  = π (0, Int64)
│   %2  = Base.arrayref(true, itr, 1)::Any
│   %3  = invoke func(%2::Any)::Any
│   %4  = (%1 + %3)::Any
│   %5  = Base.arrayref(true, itr, 2)::Any
│   %6  = invoke func(%5::Any)::Any
│   %7  = (%4 + %6)::Any
│   %8  = Base.arrayref(true, itr, 3)::Any
│   %9  = ... (continued)

73640 of 83858 relevant lines covered (87.82%)

34383713.13 hits per line

Jobs
ID Job ID Ran Files Coverage
1 #37547.1 347
87.82
Source Files on build #37547