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select-keys uses not= to compare keywords. Instead, using keyword-identical? results in decent speedups (an average of 1.34 across benchmarks and engines). Note that using identical? and lookup-sentinel doesn't appear to improve perf.

Speedup Summary:

```
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```

```
V8: 1.15, 1.08, 1.08
SpiderMonkey: 1.71, 1.48, 1.67
JavaScriptCore: 1.33, 1.35, 1.25
Nashorn: 1.16, 1.04, 0.97
ChakraCore: 1.59, 1.66, 1.72
```

Before:

```
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```

```
Benchmarking with V8
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 179 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 121 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 183 msecs
Benchmarking with SpiderMonkey
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 251 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 201 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 290 msecs
Benchmarking with JavaScriptCore
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 112 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 73 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 119 msecs
Benchmarking with Nashorn
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 1277 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 524 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 635 msecs
Benchmarking with ChakraCore
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 463 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 268 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 414 msecs
```

After

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```

```
Benchmarking with V8
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 155 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 112 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 169 msecs
Benchmarking with SpiderMonkey
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 146 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 135 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 173 msecs
Benchmarking with JavaScriptCore
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 84 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 54 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 95 msecs
Benchmarking with Nashorn
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 1099 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 502 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 648 msecs
Benchmarking with ChakraCore
;;; select-keys
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c]), 200000 runs, 292 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :x]), 200000 runs, 151 msecs
[m {:a 1, :b 2, :c 3, :d 4}], (select-keys m [:a :b :c :x :y :z]), 200000 runs, 240 msecs
```

None

David Nolen

Mike Fikes

None

Code and Test

1.9.908

Minor