go/printer: avoid allocating for every position printed
printer.print is an overloaded method for multiple purposes.
When fed a position, it updates the current position.
When fed a string, it prints the string.
When fed a token, it prints the token. And so on.
However, this overloading comes at a significant cost.
Because the parameters are a list of the `any` interface type,
any type which is not of pointer or interface kind will allocate when
passed as an argument, as interfaces can only contain pointers.
A large portion of the arguments passed to the print method are of type
token.Pos, whose underlying type is int - so it allocates.
Removing those allocations has a significant benefit,
at the cost of some verbosity in the code:
name old time/op new time/op delta
Print-16 6.10ms ± 2% 5.39ms ± 2% -11.72% (p=0.000 n=10+10)
name old speed new speed delta
Print-16 8.50MB/s ± 2% 9.63MB/s ± 2% +13.28% (p=0.000 n=10+10)
name old alloc/op new alloc/op delta
Print-16 443kB ± 0% 332kB ± 0% -25.10% (p=0.000 n=10+9)
name old allocs/op new allocs/op delta
Print-16 17.3k ± 0% 3.5k ± 0% -80.10% (p=0.000 n=10+10)
There should be more significant speed-ups left, particularly for the
token.Token, string, and whiteSpace types fed to the same method.
They are left for a future CL, in case this kind of optimization is not
a path we want to take.
Change-Id: I3ff8387242c5a935bb003e60e0813b7b9c65402e
Reviewed-on: https://go-review.googlesource.com/c/go/+/412557
Run-TryBot: Daniel Martí <mvdan@mvdan.cc> Reviewed-by: hopehook <hopehook@qq.com> Reviewed-by: Roland Shoemaker <roland@golang.org> Reviewed-by: Robert Griesemer <gri@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>