Optimize global identifier access a bit and reduce allocations

[lahma]

Paying some debt from let/const, let see what low-hanging fruit we can find.

[lahma]

Esprima.Benchmark.SunSpiderBenchmark

Diff	Method	FileName	Mean	Error	Gen 0	Gen 1	Gen 2	Allocated
Old	Run	3d-cube	636.8 ms	1.82 ms	12000.0000	1000.0000	0.0000	52.64 MB
New			658.7 ms (+3%)	3.14 ms	12000.0000 (0%)	1000.0000 (0%)	0.0000	52.59 MB (0%)
Old	Run	3d-morph	518.2 ms	1.85 ms	12000.0000	2000.0000	0.0000	78.1 MB
New			474.4 ms (-8%)	2.12 ms	12000.0000 (0%)	2000.0000 (0%)	0.0000	75.12 MB (-4%)
Old	Run	3d-raytrace	440.2 ms	1.07 ms	23000.0000	3000.0000	0.0000	96.09 MB
New			439.4 ms (0%)	1.00 ms	23000.0000 (0%)	3000.0000 (0%)	0.0000	96 MB (0%)
Old	Run	access-binary-trees	215.0 ms	0.35 ms	20000.0000	1000.0000	0.0000	83.13 MB
New			212.3 ms (-1%)	1.13 ms	20000.0000 (0%)	2000.0000 (+100%)	0.0000	83.01 MB (0%)
Old	Run	access-fannkuch	1,561.0 ms	5.38 ms	9000.0000	0.0000	0.0000	37.95 MB
New			1,560.9 ms (0%)	5.01 ms	9000.0000 (0%)	0.0000	0.0000	37.94 MB (0%)
Old	Run	access-nbody	538.5 ms	1.59 ms	15000.0000	0.0000	0.0000	62.82 MB
New			517.3 ms (-4%)	2.83 ms	15000.0000 (0%)	0.0000	0.0000	62.81 MB (0%)
Old	Run	access-nsieve	589.1 ms	1.61 ms	17000.0000	5000.0000	1000.0000	85.24 MB
New			592.4 ms (+1%)	3.62 ms	17000.0000 (0%)	5000.0000 (0%)	1000.0000 (0%)	85.24 MB (0%)
Old	Run	bitop(...)-byte [24]	395.1 ms	1.00 ms	18000.0000	0.0000	0.0000	75.18 MB
New			407.1 ms (+3%)	1.16 ms	18000.0000 (0%)	0.0000	0.0000	75.18 MB (0%)
Old	Run	bitops-bits-in-byte	643.8 ms	2.47 ms	12000.0000	0.0000	0.0000	49.87 MB
New			668.9 ms (+4%)	2.89 ms	12000.0000 (0%)	0.0000	0.0000	49.87 MB (0%)
Old	Run	bitops-bitwise-and	651.0 ms	1.91 ms	18000.0000	0.0000	0.0000	77.53 MB
New			287.0 ms (-56%)	1.84 ms	13000.0000 (-28%)	0.0000	0.0000	54.64 MB (-30%)
Old	Run	bitops-nsieve-bits	600.4 ms	2.25 ms	24000.0000	1000.0000	0.0000	99.28 MB
New			595.4 ms (-1%)	1.95 ms	24000.0000 (0%)	1000.0000 (0%)	0.0000	98.44 MB (-1%)
Old	Run	contr(...)rsive [21]	307.9 ms	1.19 ms	32000.0000	0.0000	0.0000	128.3 MB
New			299.5 ms (-3%)	0.87 ms	32000.0000 (0%)	0.0000	0.0000	128.3 MB (0%)
Old	Run	crypto-aes	417.4 ms	0.91 ms	6000.0000	1000.0000	0.0000	28.21 MB
New			401.8 ms (-4%)	0.49 ms	6000.0000 (0%)	1000.0000 (0%)	0.0000	28.21 MB (0%)
Old	Run	crypto-md5	268.8 ms	1.98 ms	24000.0000	2000.0000	0.0000	99.17 MB
New			258.0 ms (-4%)	0.79 ms	24000.0000 (0%)	2000.0000 (0%)	0.0000	99.15 MB (0%)
Old	Run	crypto-sha1	271.4 ms	0.48 ms	21000.0000	1000.0000	0.0000	86.89 MB
New			263.7 ms (-3%)	0.44 ms	21000.0000 (0%)	1000.0000 (0%)	0.0000	86.88 MB (0%)
Old	Run	date-format-tofte	310.9 ms	0.46 ms	17000.0000	1000.0000	0.0000	70.32 MB
New			317.5 ms (+2%)	0.67 ms	17000.0000 (0%)	0.0000 (-100%)	0.0000	69.69 MB (-1%)
Old	Run	date-format-xparb	154.2 ms	0.58 ms	7000.0000	1000.0000	0.0000	29.76 MB
New			141.4 ms (-8%)	0.43 ms	7000.0000 (0%)	1000.0000 (0%)	0.0000	29.49 MB (-1%)
Old	Run	math-cordic	972.7 ms	2.65 ms	31000.0000	0.0000	0.0000	126.66 MB
New			913.7 ms (-6%)	2.69 ms	31000.0000 (0%)	0.0000	0.0000	124.18 MB (-2%)
Old	Run	math-partial-sums	387.9 ms	0.47 ms	15000.0000	0.0000	0.0000	63.5 MB
New			331.0 ms (-15%)	1.42 ms	14000.0000 (-7%)	0.0000	0.0000	56.72 MB (-11%)
Old	Run	math-spectral-norm	304.3 ms	0.95 ms	18000.0000	0.0000	0.0000	72.29 MB
New			303.3 ms (0%)	0.83 ms	18000.0000 (0%)	0.0000	0.0000	72.28 MB (0%)
Old	Run	regexp-dna	450.8 ms	0.97 ms	0.0000	0.0000	0.0000	18.31 MB
New			436.4 ms (-3%)	1.46 ms	0.0000	0.0000	0.0000	18.3 MB (0%)
Old	Run	string-base64	239.3 ms	0.92 ms	3000.0000	1000.0000	0.0000	13.76 MB
New			227.5 ms (-5%)	0.64 ms	3000.0000 (0%)	1000.0000 (0%)	0.0000	12.38 MB (-10%)
Old	Run	string-fasta	558.6 ms	1.26 ms	41000.0000	0.0000	0.0000	165.85 MB
New			527.5 ms (-6%)	0.65 ms	40000.0000 (-2%)	0.0000	0.0000	161.73 MB (-2%)
Old	Run	string-tagcloud	200.3 ms	0.66 ms	11000.0000	1000.0000	0.0000	56 MB
New			198.3 ms (-1%)	0.59 ms	11000.0000 (0%)	1000.0000 (0%)	0.0000	56 MB (0%)
Old	Run	string-unpack-code	204.7 ms	0.54 ms	20000.0000	3000.0000	1000.0000	89.33 MB
New			209.5 ms (+2%)	2.43 ms	20000.0000 (0%)	3000.0000 (0%)	1000.0000 (0%)	89.33 MB (0%)
Old	Run	strin(...)input [21]	1,263.4 ms	16.24 ms	1161000.0000	1141000.0000	1140000.0000	6211.46 MB
New			1,286.7 ms (+2%)	14.41 ms	1160000.0000 (0%)	1140000.0000 (0%)	1139000.0000 (0%)	6211.18 MB (0%)

Jint.Benchmark.ArrayBenchmark

Diff	Method	N	Mean	Error	Gen 0	Gen 1	Gen 2	Allocated
Old	Slice	100	546.8 μs	1.03 μs	181.6406	0.0000	0.0000	742.19 KB
New			539.2 μs (-1%)	1.22 μs	180.6641 (-1%)	0.0000	0.0000	739.84 KB (0%)
Old	Concat	100	754.0 μs	1.85 μs	216.7969	0.0000	0.0000	886.72 KB
New			735.2 μs (-2%)	3.64 μs	215.8203 (0%)	0.0000	0.0000	884.38 KB (0%)
Old	Unshift	100	22,095.3 μs	156.94 μs	3875.0000	0.0000	0.0000	15831.25 KB
New			17,989.2 μs (-19%)	113.02 μs	3718.7500 (-4%)	0.0000	0.0000	15229.69 KB (-4%)
Old	Push	100	14,016.3 μs	51.30 μs	640.6250	0.0000	0.0000	2679.69 KB
New			9,806.0 μs (-30%)	40.84 μs	500.0000 (-22%)	0.0000	0.0000	2075.07 KB (-23%)
Old	Index	100	15,463.1 μs	32.26 μs	828.1250	0.0000	0.0000	3422.66 KB
New			10,485.9 μs (-32%)	12.05 μs	687.5000 (-17%)	0.0000	0.0000	2810.94 KB (-18%)
Old	Map	100	5,057.3 μs	23.63 μs	1156.2500	0.0000	0.0000	4726.58 KB
New			4,936.5 μs (-2%)	23.77 μs	1148.4375 (-1%)	0.0000	0.0000	4713.28 KB (0%)
Old	Apply	100	771.7 μs	2.63 μs	215.8203	0.0000	0.0000	884.38 KB
New			751.4 μs (-3%)	3.10 μs	213.8672 (-1%)	0.0000	0.0000	877.34 KB (-1%)
Old	JsonStringifyParse	100	4,797.2 μs	11.44 μs	1304.6875	0.0000	0.0000	5332.06 KB
New			5,032.1 μs (+5%)	18.13 μs	1296.8750 (-1%)	0.0000	0.0000	5325.03 KB (0%)
Old	FilterWithString	100	53,161.0 μs	556.09 μs	10700.0000	0.0000	0.0000	43885.16 KB
New			53,584.9 μs (+1%)	318.64 μs	10700.0000 (0%)	0.0000	0.0000	43880.47 KB (0%)

Jint.Benchmark.DromaeoBenchmark

Diff	Method	FileName	Mean	Error	Gen 0	Gen 1	Gen 2	Allocated
Old	Run	dromaeo-3d-cube	71.86 ms	0.169 ms	1571.4286	285.7143	0.0000	8614.83 KB
New			71.37 ms (-1%)	0.197 ms	1571.4286 (0%)	428.5714 (+50%)	0.0000	8591.82 KB (0%)
Old	Run	dromaeo-core-eval	19.94 ms	0.140 ms	125.0000	0.0000	0.0000	523.86 KB
New			20.62 ms (+3%)	0.079 ms	125.0000 (0%)	0.0000	0.0000	516.75 KB (-1%)
Old	Run	dromaeo-object-array	202.70 ms	0.766 ms	41000.0000	2000.0000	0.0000	175886.27 KB
New			173.02 ms (-15%)	0.299 ms	41000.0000 (0%)	2000.0000 (0%)	0.0000	174220.34 KB (-1%)
Old	Run	droma(...)egexp [21]	777.24 ms	8.664 ms	42000.0000	23000.0000	13000.0000	373138.83 KB
New			707.44 ms (-9%)	13.006 ms	44000.0000 (+5%)	27000.0000 (+17%)	18000.0000 (+38%)	373249.54 KB (0%)
Old	Run	droma(...)tring [21]	714.37 ms	4.881 ms	109000.0000	73000.0000	72000.0000	1349482.74 KB
New			597.43 ms (-16%)	7.110 ms	108000.0000 (-1%)	74000.0000 (+1%)	72000.0000 (0%)	1341766.19 KB (-1%)
Old	Run	droma(...)ase64 [21]	156.76 ms	0.772 ms	2000.0000	0.0000	0.0000	8961.59 KB
New			148.97 ms (-5%)	2.250 ms	2000.0000 (0%)	0.0000	0.0000	8672.23 KB (-3%)

Jint.Benchmark.UncacheableExpressionsBenchmark

Diff	Method	N	Mean	Error	Gen 0	Gen 1	Gen 2	Allocated
Old	Benchmark	500	310.2 ms	1.08 ms	49000.0000	2000.0000	0.0000	195.92 MB
New			320.9 ms (+3%)	2.42 ms	49000.0000 (0%)	2000.0000 (0%)	0.0000	195.92 MB (0%)
Old	Benchmark	500	235.5 ms	0.93 ms	43000.0000	11000.0000	0.0000	173.43 MB
New			245.0 ms (+4%)	0.97 ms	43000.0000 (0%)	11000.0000 (0%)	0.0000	173.43 MB (0%)