From: Josh Bleecher Snyder Date: Sun, 26 Mar 2017 22:16:11 +0000 (-0700) Subject: cmd/internal/dwarf: remove global encbuf X-Git-Tag: go1.9beta1~961 X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=f97830114497d88a980859440bea51b252d0601e;p=gostls13.git cmd/internal/dwarf: remove global encbuf The global encbuf helped avoid allocations. It is incompatible with a concurrent backend. To avoid a performance regression while removing it, introduce two optimizations. First, re-use a buffer in dwarf.PutFunc. Second, avoid a buffer entirely when the int being encoded fits in seven bits, which is about 75% of the time. Passes toolstash-check. Updates #15756 name old alloc/op new alloc/op delta Template 40.6MB ± 0% 40.6MB ± 0% -0.08% (p=0.001 n=8+9) Unicode 29.9MB ± 0% 29.9MB ± 0% ~ (p=0.068 n=8+10) GoTypes 116MB ± 0% 116MB ± 0% +0.05% (p=0.043 n=10+9) SSA 864MB ± 0% 864MB ± 0% +0.01% (p=0.010 n=10+9) Flate 25.8MB ± 0% 25.8MB ± 0% ~ (p=0.353 n=10+10) GoParser 32.2MB ± 0% 32.2MB ± 0% ~ (p=0.353 n=10+10) Reflect 80.2MB ± 0% 80.2MB ± 0% ~ (p=0.165 n=10+10) Tar 27.0MB ± 0% 26.9MB ± 0% ~ (p=0.143 n=10+10) XML 42.8MB ± 0% 42.8MB ± 0% ~ (p=0.400 n=10+9) name old allocs/op new allocs/op delta Template 398k ± 0% 397k ± 0% -0.20% (p=0.002 n=8+9) Unicode 320k ± 0% 321k ± 1% ~ (p=0.122 n=8+10) GoTypes 1.16M ± 0% 1.17M ± 0% ~ (p=0.053 n=10+9) SSA 7.65M ± 0% 7.65M ± 0% ~ (p=0.122 n=10+8) Flate 240k ± 1% 240k ± 1% ~ (p=0.243 n=10+9) GoParser 322k ± 1% 322k ± 1% ~ (p=0.481 n=10+10) Reflect 1.00M ± 0% 1.00M ± 0% ~ (p=0.211 n=9+10) Tar 256k ± 0% 255k ± 1% ~ (p=0.052 n=10+10) XML 400k ± 1% 400k ± 0% ~ (p=0.631 n=10+10) Change-Id: Ia39d9de09232fdbfc9c9cec14587bbf6939c9492 Reviewed-on: https://go-review.googlesource.com/38713 Run-TryBot: Josh Bleecher Snyder Reviewed-by: Brad Fitzpatrick --- diff --git a/src/cmd/internal/dwarf/dwarf.go b/src/cmd/internal/dwarf/dwarf.go index 99cb2d53ce..7625149914 100644 --- a/src/cmd/internal/dwarf/dwarf.go +++ b/src/cmd/internal/dwarf/dwarf.go @@ -7,7 +7,9 @@ // this package contains the shared code. package dwarf -import "fmt" +import ( + "fmt" +) // InfoPrefix is the prefix for all the symbols containing DWARF info entries. const InfoPrefix = "go.info." @@ -68,17 +70,56 @@ func AppendSleb128(b []byte, v int64) []byte { return b } -var encbuf [20]byte +// sevenbits contains all unsigned seven bit numbers, indexed by their value. +var sevenbits = [...]byte{ + 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f, + 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f, + 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f, + 0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f, + 0x40, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4c, 0x4d, 0x4e, 0x4f, + 0x50, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5b, 0x5c, 0x5d, 0x5e, 0x5f, + 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, + 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, +} + +// sevenBitU returns the unsigned LEB128 encoding of v if v is seven bits and nil otherwise. +// The contents of the returned slice must not be modified. +func sevenBitU(v int64) []byte { + if uint64(v) < uint64(len(sevenbits)) { + return sevenbits[v : v+1] + } + return nil +} -// AppendUleb128 appends v to s using DWARF's unsigned LEB128 encoding. +// sevenBitS returns the signed LEB128 encoding of v if v is seven bits and nil otherwise. +// The contents of the returned slice must not be modified. +func sevenBitS(v int64) []byte { + if uint64(v) <= 63 { + return sevenbits[v : v+1] + } + if uint64(-v) <= 64 { + return sevenbits[128+v : 128+v+1] + } + return nil +} + +// Uleb128put appends v to s using DWARF's unsigned LEB128 encoding. func Uleb128put(ctxt Context, s Sym, v int64) { - b := AppendUleb128(encbuf[:0], uint64(v)) + b := sevenBitU(v) + if b == nil { + var encbuf [20]byte + b = AppendUleb128(encbuf[:0], uint64(v)) + } ctxt.AddBytes(s, b) } -// AppendUleb128 appends v to s using DWARF's signed LEB128 encoding. +// Sleb128put appends v to s using DWARF's signed LEB128 encoding. func Sleb128put(ctxt Context, s Sym, v int64) { - b := AppendSleb128(encbuf[:0], v) + b := sevenBitS(v) + if b == nil { + var encbuf [20]byte + b = AppendSleb128(encbuf[:0], v) + } ctxt.AddBytes(s, b) } @@ -396,7 +437,6 @@ func GetAbbrev() []byte { for i := 1; i < DW_NABRV; i++ { // See section 7.5.3 buf = AppendUleb128(buf, uint64(i)) - buf = AppendUleb128(buf, uint64(abbrevs[i].tag)) buf = append(buf, byte(abbrevs[i].children)) for _, f := range abbrevs[i].attr { @@ -572,6 +612,7 @@ func PutFunc(ctxt Context, s Sym, name string, external bool, startPC Sym, size } putattr(ctxt, s, DW_ABRV_FUNCTION, DW_FORM_flag, DW_CLS_FLAG, ev, 0) names := make(map[string]bool) + var encbuf [20]byte for _, v := range vars { var n string if names[v.Name] { @@ -591,7 +632,6 @@ func PutFunc(ctxt Context, s Sym, name string, external bool, startPC Sym, size } putattr(ctxt, s, v.Abbrev, DW_FORM_block1, DW_CLS_BLOCK, int64(len(loc)), loc) putattr(ctxt, s, v.Abbrev, DW_FORM_ref_addr, DW_CLS_REFERENCE, 0, v.Type) - } Uleb128put(ctxt, s, 0) } diff --git a/src/cmd/internal/dwarf/dwarf_test.go b/src/cmd/internal/dwarf/dwarf_test.go new file mode 100644 index 0000000000..248a39b54e --- /dev/null +++ b/src/cmd/internal/dwarf/dwarf_test.go @@ -0,0 +1,38 @@ +// Copyright 2017 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package dwarf + +import ( + "reflect" + "testing" +) + +func TestSevenBitEnc128(t *testing.T) { + t.Run("unsigned", func(t *testing.T) { + for v := int64(-255); v < 255; v++ { + s := sevenBitU(v) + if s == nil { + continue + } + b := AppendUleb128(nil, uint64(v)) + if !reflect.DeepEqual(b, s) { + t.Errorf("sevenBitU(%d) = %v but AppendUleb128(%d) = %v", v, s, v, b) + } + } + }) + + t.Run("signed", func(t *testing.T) { + for v := int64(-255); v < 255; v++ { + s := sevenBitS(v) + if s == nil { + continue + } + b := AppendSleb128(nil, v) + if !reflect.DeepEqual(b, s) { + t.Errorf("sevenBitS(%d) = %v but AppendSleb128(%d) = %v", v, s, v, b) + } + } + }) +}