The move to 64-bit ints in 6g made componentgen ineffective.
In componentgen, the code already selects which values it can handle.

On amd64:
benchmark                 old ns/op    new ns/op    delta
BenchmarkBinaryTree17    9477970000   9582314000   +1.10%
BenchmarkFannkuch11      5928750000   5255080000  -11.36%
BenchmarkGobDecode         37103040     31451120  -15.23%
BenchmarkGobEncode         16042490     16844730   +5.00%
BenchmarkGzip             811337400    741373600   -8.62%
BenchmarkGunzip           197928700    192844500   -2.57%
BenchmarkJSONEncode       224164100    140064200  -37.52%
BenchmarkJSONDecode       258346800    231829000  -10.26%
BenchmarkMandelbrot200      7561780      7601615   +0.53%
BenchmarkParse             12970340     11624360  -10.38%
BenchmarkRevcomp         1969917000   1699137000  -13.75%
BenchmarkTemplate         296182000    263117400  -11.16%

R=nigeltao, dave, daniel.morsing
CC=golang-dev
https://golang.org/cl/6821052