Make opt_eq and opt_neq insns leaf

# Benchmark zero?

```
require 'benchmark/ips'

Numeric.class_eval do
  def ruby_zero?
    self == 0
  end
end

Benchmark.ips do |x|
  x.report('0.zero?') { 0.ruby_zero? }
  x.report('1.zero?') { 1.ruby_zero? }
  x.compare!
end
```

## VM
No significant impact for VM.

### before
ruby 2.7.0dev (2019-08-04T02:56:02Z master 2d8c037e97) [x86_64-linux]

  0.zero?: 21855445.5 i/s
  1.zero?: 21770817.3 i/s - same-ish: difference falls within error

### after
ruby 2.7.0dev (2019-08-04T11:17:10Z opt-eq-leaf 6404bebd6a) [x86_64-linux]

  1.zero?: 21958912.3 i/s
  0.zero?: 21881625.9 i/s - same-ish: difference falls within error

## JIT
The performance improves about 1.23x.

### before
ruby 2.7.0dev (2019-08-04T02:56:02Z master 2d8c037e97) +JIT [x86_64-linux]

  0.zero?: 36343111.6 i/s
  1.zero?: 36295153.3 i/s - same-ish: difference falls within error

### after
ruby 2.7.0dev (2019-08-04T11:17:10Z opt-eq-leaf 6404bebd6a) +JIT [x86_64-linux]

  0.zero?: 44740467.2 i/s
  1.zero?: 44363616.1 i/s - same-ish: difference falls within error

# Benchmark str == str / str != str

```
# frozen_string_literal: true
require 'benchmark/ips'

Benchmark.ips do |x|
  x.report('a == a') { 'a' == 'a' }
  x.report('a == b') { 'a' == 'b' }
  x.report('a != a') { 'a' != 'a' }
  x.report('a != b') { 'a' != 'b' }
  x.compare!
end
```

## VM
No significant impact for VM.

### before
ruby 2.7.0dev (2019-08-04T02:56:02Z master 2d8c037e97) [x86_64-linux]

  a == a: 27286219.0 i/s
  a != a: 24892389.5 i/s - 1.10x  slower
  a == b: 23623635.8 i/s - 1.16x  slower
  a != b: 21800958.0 i/s - 1.25x  slower

### after
ruby 2.7.0dev (2019-08-04T11:17:10Z opt-eq-leaf 6404bebd6a) [x86_64-linux]

  a == a: 27224016.2 i/s
  a != a: 24490109.5 i/s - 1.11x  slower
  a == b: 23391052.4 i/s - 1.16x  slower
  a != b: 21811321.7 i/s - 1.25x  slower

## JIT
The performance improves on JIT a little.

### before
ruby 2.7.0dev (2019-08-04T02:56:02Z master 2d8c037e97) +JIT [x86_64-linux]

  a == a: 42010674.7 i/s
  a != a: 38920311.2 i/s - same-ish: difference falls within error
  a == b: 32574262.2 i/s - 1.29x  slower
  a != b: 32099790.3 i/s - 1.31x  slower

### after
ruby 2.7.0dev (2019-08-04T11:17:10Z opt-eq-leaf 6404bebd6a) +JIT [x86_64-linux]

  a == a: 46902738.8 i/s
  a != a: 43097258.6 i/s - 1.09x  slower
  a == b: 35822018.4 i/s - 1.31x  slower
  a != b: 33377257.8 i/s - 1.41x  slower

This is needed towards Bug#15589.
Closes: https://github.com/ruby/ruby/pull/2318

1 files changed, 5 insertions, 4 deletions

diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 1875d35de1..e68ded7d15 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -1506,10 +1506,11 @@ opt_eq_func(VALUE recv, VALUE obj, CALL_INFO ci, CALL_CACHE cc)
 	    return rb_float_equal(recv, obj);
 	}
     }
-    else if (BUILTIN_CLASS_P(recv, rb_cString)) {
-	if (EQ_UNREDEFINED_P(STRING)) {
-	    return rb_str_equal(recv, obj);
-	}
+    else if (BUILTIN_CLASS_P(recv, rb_cString) && EQ_UNREDEFINED_P(STRING)) {
+        if (recv == obj) return Qtrue;
+        if (RB_TYPE_P(obj, T_STRING)) {
+            return rb_str_eql_internal(recv, obj);
+        }
     }
 
   fallback: