cmd/gc: optimize memclr of slices and arrays
Recognize loops of the form for i := range a { a[i] = zero } in which the evaluation of a is free from side effects. Replace these loops with calls to memclr. This occurs in the stdlib in 18 places. The motivating example is clearing a byte slice: benchmark old ns/op new ns/op delta BenchmarkGoMemclr5 3.31 3.26 -1.51% BenchmarkGoMemclr16 13.7 3.28 -76.06% BenchmarkGoMemclr64 50.8 4.14 -91.85% BenchmarkGoMemclr256 157 6.02 -96.17% Update #5373. Change-Id: I99d3e6f5f268e8c6499b7e661df46403e5eb83e4 Reviewed-on: https://go-review.googlesource.com/2520Reviewed-by:Keith Randall <khr@golang.org>
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test/fixedbugs/issue5373.go
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