internal/fuzz: limit number of consecutive mutations
This makes two changes: (1) mutator.mutate now only applies a single
mutation to the input, and (2) in workerServer.fuzz if, after five
mutations are applied to the input, no new coverage is found the input
is reset to its initial state. This process is repeated until new
coverage is found, or the fuzz call times out.
This results in finding new coverage expanding inputs which have less
divergence from the initial input they were mutated from, which makes
traversing certain types of call graphs significantly more efficient.
Fixes #49601
Fixes #48179
Fixes #47090
Change-Id: I74d18a56ca2669f20192951090b281f58ee0b5dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/364214
Trust: Roland Shoemaker <roland@golang.org>
Trust: Katie Hockman <katie@golang.org>
Run-TryBot: Roland Shoemaker <roland@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Katie Hockman <katie@golang.org>