Replace by a left shift and an addition. Generated code for 64 bits
version already map to the even most adequate `LEA`.
On a mid-2012 MBA,
benchmark old MB/s new MB/s speedup
Benchmark32_1-4 90.18 91.08 1.01x
Benchmark32_2-4 168.26 168.55 1.00x
Benchmark32_4-4 342.13 338.26 0.99x
Benchmark32_8-4 587.46 584.68 1.00x
Benchmark32_16-4 981.80 990.72 1.01x
Benchmark32_32-4 1349.67 1370.62 1.02x
Benchmark32_64-4 1684.94 1696.83 1.01x
Benchmark32_128-4 1748.24 1746.80 1.00x
Benchmark32_256-4 1805.96 1933.24 1.07x
Benchmark32_512-4 1845.56 2019.75 1.09x
Benchmark32_1024-4 1856.36 2031.61 1.09x
Benchmark32_2048-4 1890.43 2032.47 1.08x
Benchmark32_4096-4 1881.13 2085.36 1.11x
Benchmark32_8192-4 1889.83 2103.02 1.11x