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cmd/compile: de-virtualize interface calls

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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: I57d4dc21ef40a05ec0fbd55a9bb0eb74cdc67a3d
Reviewed-on: https://go-review.googlesource.com/38139
Run-TryBot: Philip Hofer <phofer@umich.edu>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
This commit is contained in:
philhofer 2017-03-13 15:03:17 -07:00 • committed by David Chase
parent 691755304c
commit 295307ae78
10 changed files with 234 additions and 17 deletions
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31
src/cmd/compile/internal/ssa/export_test.go
View file

@ -97,21 +97,22 @@ func (d DummyFrontend) Warnl(_ src.XPos, msg string, args ...interface{}) { d.t
func (d DummyFrontend) Debug_checknil() bool { return false }
func (d DummyFrontend) Debug_wb() bool { return false }
func (d DummyFrontend) TypeBool() Type { return TypeBool }
func (d DummyFrontend) TypeInt8() Type { return TypeInt8 }
func (d DummyFrontend) TypeInt16() Type { return TypeInt16 }
func (d DummyFrontend) TypeInt32() Type { return TypeInt32 }
func (d DummyFrontend) TypeInt64() Type { return TypeInt64 }
func (d DummyFrontend) TypeUInt8() Type { return TypeUInt8 }
func (d DummyFrontend) TypeUInt16() Type { return TypeUInt16 }
func (d DummyFrontend) TypeUInt32() Type { return TypeUInt32 }
func (d DummyFrontend) TypeUInt64() Type { return TypeUInt64 }
func (d DummyFrontend) TypeFloat32() Type { return TypeFloat32 }
func (d DummyFrontend) TypeFloat64() Type { return TypeFloat64 }
func (d DummyFrontend) TypeInt() Type { return TypeInt64 }
func (d DummyFrontend) TypeUintptr() Type { return TypeUInt64 }
func (d DummyFrontend) TypeString() Type { panic("unimplemented") }
func (d DummyFrontend) TypeBytePtr() Type { return TypeBytePtr }
func (d DummyFrontend) TypeBool() Type { return TypeBool }
func (d DummyFrontend) TypeInt8() Type { return TypeInt8 }
func (d DummyFrontend) TypeInt16() Type { return TypeInt16 }
func (d DummyFrontend) TypeInt32() Type { return TypeInt32 }
func (d DummyFrontend) TypeInt64() Type { return TypeInt64 }
func (d DummyFrontend) TypeUInt8() Type { return TypeUInt8 }
func (d DummyFrontend) TypeUInt16() Type { return TypeUInt16 }
func (d DummyFrontend) TypeUInt32() Type { return TypeUInt32 }
func (d DummyFrontend) TypeUInt64() Type { return TypeUInt64 }
func (d DummyFrontend) TypeFloat32() Type { return TypeFloat32 }
func (d DummyFrontend) TypeFloat64() Type { return TypeFloat64 }
func (d DummyFrontend) TypeInt() Type { return TypeInt64 }
func (d DummyFrontend) TypeUintptr() Type { return TypeUInt64 }
func (d DummyFrontend) TypeString() Type { panic("unimplemented") }
func (d DummyFrontend) TypeBytePtr() Type { return TypeBytePtr }
func (d DummyFrontend) DerefItab(sym *obj.LSym, off int64) *obj.LSym { return nil }
func (d DummyFrontend) CanSSA(t Type) bool {
// There are no un-SSAable types in dummy land.