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c20e819e8b
The following code previously caused a crash:
```ruby
h = {}
1000000.times{|i| h[i.to_s.to_sym] = i}
def f(kw: 1, **kws) end
f(**h)
```
Inside a thread or fiber, the size of the keyword splat could be much smaller
and still cause a crash.
I found this issue while optimizing method calling by reducing implicit
allocations. Given the following code:
```ruby
def f(kw: , **kws) end
kw = {kw: 1}
f(**kw)
```
The `f(**kw)` call previously allocated two hashes callee side instead of a
single hash. This is because `setup_parameters_complex` would extract the
keywords from the keyword splat hash to the C stack, to attempt to mirror
the case when literal keywords are passed without a keyword splat. Then,
`make_rest_kw_hash` would build a new hash based on the extracted keywords
that weren't used for literal keywords.
Switch the implementation so that if a keyword splat is passed, literal keywords
are deleted from the keyword splat hash (or a copy of the hash if the hash is
not mutable).
In addition to avoiding the crash, this new approach is much more
efficient in all cases. With the included benchmark:
```
1
miniruby: 5247879.9 i/s
miniruby-before: 2474050.2 i/s - 2.12x slower
1_mutable
miniruby: 1797036.5 i/s
miniruby-before: 1239543.3 i/s - 1.45x slower
10
miniruby: 1094750.1 i/s
miniruby-before: 365529.6 i/s - 2.99x slower
10_mutable
miniruby: 407781.7 i/s
miniruby-before: 225364.0 i/s - 1.81x slower
100
miniruby: 100992.3 i/s
miniruby-before: 32703.6 i/s - 3.09x slower
100_mutable
miniruby: 40092.3 i/s
miniruby-before: 21266.9 i/s - 1.89x slower
1000
miniruby: 21694.2 i/s
miniruby-before: 4949.8 i/s - 4.38x slower
1000_mutable
miniruby: 5819.5 i/s
miniruby-before: 2995.0 i/s - 1.94x slower
```