From: "tenderlovemaking (Aaron Patterson)" <noreply@...>
Date: 2022-06-13T16:49:06+00:00
Subject: [ruby-core:108877] [Ruby master Feature#18825] Specialized instruction for "array literal + `.hash`"

Issue #18825 has been reported by tenderlovemaking (Aaron Patterson).

----------------------------------------
Feature #18825: Specialized instruction for "array literal + `.hash`"
https://bugs.ruby-lang.org/issues/18825

* Author: tenderlovemaking (Aaron Patterson)
* Status: Open
* Priority: Normal
----------------------------------------
Feature #18611 is merged.  That feature encourages people to write hash methods like this:

```
def hash
  [@a, @b, @c].hash
end
```

I would like to add a specialized instruction for this case `opt_newarray_hash`.  It's similar to `opt_newarray_max` and `opt_newarray_min` but for the hash method.

ISeqs before the optimization:

```
== disasm: #<ISeq:hash@test.rb:1 (1,0)-(3,3)> (catch: FALSE)
0000 getinstancevariable          :@a, <is:0>                         (   2)[LiCa]
0003 getinstancevariable          :@b, <is:1>
0006 getinstancevariable          :@c, <is:2>
0009 newarray                     3
0011 opt_send_without_block       <callinfo!mid:hash, argc:0, ARGS_SIMPLE>, <callcache>
0014 leave  
```

ISeqs after the optimization:

```
== disasm: #<ISeq:hash@test.rb:1 (1,0)-(3,3)> (catch: FALSE)
0000 getinstancevariable                    :@a, <is:0>               (   2)[LiCa]
0003 getinstancevariable                    :@b, <is:1>
0006 getinstancevariable                    :@c, <is:2>
0009 opt_newarray_hash                      3
0011 leave  
```

The new instruction allows us to avoid allocating a new array and also avoid pushing a stack frame.

The implementation is [here](https://github.com/ruby/ruby/pull/5980), and I've also attached a patch.

---Files--------------------------------
0001-Emit-special-instruction-for-array-literal-.hash.patch (4.91 KB)


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