1581bb9843
Using go/types to get rid of all unused variables in CL 189798 was a neat idea, but it was pretty expensive. go/types is a full typechecker, which does a lot more work than we actually need. Moreover, we had to run it multiple times, to catch variables that became unused after removing existing unused variables. Instead, write our own little detector for unused imports and variables. It doesn't use ast.Walk, as we need to know what fields we're inspecting. For example, in "foo := bar", "foo" is declared, and "bar" is used, yet they both appear as simple *ast.Ident cases under ast.Walk. The code is documented to explain how unused variables are detected in a single syntax tree pass. Since this happens after we've generated a complete go/ast.File, we don't need to worry about our own simplified node types. The generated code is the same, but rulegen is much faster and uses less memory at its peak, so it should scale better with time. With 'benchcmd Rulegen go run *.go' on perflock, we get: name old time/op new time/op delta Rulegen 4.00s ± 0% 3.41s ± 1% -14.70% (p=0.008 n=5+5) name old user-time/op new user-time/op delta Rulegen 14.1s ± 1% 10.6s ± 1% -24.62% (p=0.008 n=5+5) name old sys-time/op new sys-time/op delta Rulegen 318ms ±26% 263ms ± 9% ~ (p=0.056 n=5+5) name old peak-RSS-bytes new peak-RSS-bytes delta Rulegen 231MB ± 4% 181MB ± 3% -21.69% (p=0.008 n=5+5) Change-Id: I8387d52818f6131357868ad348dac8c96d926191 Reviewed-on: https://go-review.googlesource.com/c/go/+/191782 Run-TryBot: Daniel Martí <mvdan@mvdan.cc> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org> |
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