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4e0c7c3f61
With this change, code like
h := sha1.New()
h.Write(buf)
sum := h.Sum()
gets compiled into static calls rather than
interface calls, because the compiler is able
to prove that 'h' is really a *sha1.digest.
The InterCall re-write rule hits a few dozen times
during make.bash, and hundreds of times during all.bash.
The most common pattern identified by the compiler
is a constructor like
func New() Interface { return &impl{...} }
where the constructor gets inlined into the caller,
and the result is used immediately. Examples include
{sha1,md5,crc32,crc64,...}.New, base64.NewEncoder,
base64.NewDecoder, errors.New, net.Pipe, and so on.
Some existing benchmarks that change on darwin/amd64:
Crc64/ISO4KB-8 2.67µs ± 1% 2.66µs ± 0% -0.36% (p=0.015 n=10+10)
Crc64/ISO1KB-8 694ns ± 0% 690ns ± 1% -0.59% (p=0.001 n=10+10)
Adler32KB-8 473ns ± 1% 471ns ± 0% -0.39% (p=0.010 n=10+9)
On architectures like amd64, the reduction in code size
appears to contribute more to benchmark improvements than just
removing the indirect call, since that branch gets predicted
accurately when called in a loop.
Updates #19361
Change-Id: Ia9d30afdd5f6b4d38d38b14b88f308acae8ce7ed
Reviewed-on: https://go-review.googlesource.com/37751
Run-TryBot: Philip Hofer <phofer@umich.edu>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
64 lines
1.2 KiB
Go
64 lines
1.2 KiB
Go
// errorcheck -0 -d=ssa/opt/debug=3
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package main
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import (
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"crypto/sha1"
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"errors"
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"fmt"
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"sync"
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)
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func f0() {
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v := errors.New("error string")
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_ = v.Error() // ERROR "de-virtualizing call$"
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}
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func f1() {
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h := sha1.New()
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buf := make([]byte, 4)
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h.Write(buf) // ERROR "de-virtualizing call$"
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_ = h.Sum(nil) // ERROR "de-virtualizing call$"
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}
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func f2() {
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// trickier case: make sure we see this is *sync.rlocker
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// instead of *sync.RWMutex,
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// even though they are the same pointers
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var m sync.RWMutex
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r := m.RLocker()
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// deadlock if the type of 'r' is improperly interpreted
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// as *sync.RWMutex
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r.Lock() // ERROR "de-virtualizing call$"
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m.RLock()
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r.Unlock() // ERROR "de-virtualizing call$"
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m.RUnlock()
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}
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type multiword struct{ a, b, c int }
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func (m multiword) Error() string { return fmt.Sprintf("%d, %d, %d", m.a, m.b, m.c) }
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func f3() {
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// can't de-virtualize this one yet;
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// it passes through a call to iconvT2I
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var err error
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err = multiword{1, 2, 3}
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if err.Error() != "1, 2, 3" {
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panic("bad call")
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}
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// ... but we can do this one
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err = &multiword{1, 2, 3}
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if err.Error() != "1, 2, 3" { // ERROR "de-virtualizing call$"
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panic("bad call")
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}
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}
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func main() {
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f0()
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f1()
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f2()
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f3()
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}
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