From 39dde09126be02f5f8c38ddf7590ae8f9825fcaa Mon Sep 17 00:00:00 2001 From: Cherry Zhang Date: Mon, 21 Sep 2020 20:44:53 -0400 Subject: [PATCH] cmd/link: retain only used interface methods Currently, in the linker's deadcode pass, when an interface type is live, the linker thinks all its methods are live, and uses them to match methods on concrete types. The interface method may never be used, though. This CL changes it to only keep used interface methods, for matching concrete type methods. To do that, when an interface method is used, the compiler generates a mark relocation. The linker uses the marker relocations to mark used interface methods, and only the used ones. binary size before after cmd/compile 18887400 18812200 cmd/go 13470652 13470492 Change-Id: I3cfd9df4a53783330ba87735853f2a0ec3c42802 Reviewed-on: https://go-review.googlesource.com/c/go/+/256798 Trust: Cherry Zhang Reviewed-by: Than McIntosh Reviewed-by: Jeremy Faller --- src/cmd/compile/internal/gc/reflect.go | 19 +++++- src/cmd/compile/internal/gc/walk.go | 15 +++++ src/cmd/internal/objabi/reloctype.go | 6 ++ src/cmd/internal/objabi/reloctype_string.go | 67 ++++++++++--------- src/cmd/link/internal/ld/deadcode.go | 53 +++++++-------- src/cmd/link/internal/ld/deadcode_test.go | 1 + .../ld/testdata/deadcode/ifacemethod4.go | 23 +++++++ 7 files changed, 120 insertions(+), 64 deletions(-) create mode 100644 src/cmd/link/internal/ld/testdata/deadcode/ifacemethod4.go diff --git a/src/cmd/compile/internal/gc/reflect.go b/src/cmd/compile/internal/gc/reflect.go index 49b2a0ed49a..ae3e2f8e658 100644 --- a/src/cmd/compile/internal/gc/reflect.go +++ b/src/cmd/compile/internal/gc/reflect.go @@ -61,8 +61,9 @@ const ( MAXELEMSIZE = 128 ) -func structfieldSize() int { return 3 * Widthptr } // Sizeof(runtime.structfield{}) -func imethodSize() int { return 4 + 4 } // Sizeof(runtime.imethod{}) +func structfieldSize() int { return 3 * Widthptr } // Sizeof(runtime.structfield{}) +func imethodSize() int { return 4 + 4 } // Sizeof(runtime.imethod{}) +func commonSize() int { return 4*Widthptr + 8 + 8 } // Sizeof(runtime._type{}) func uncommonSize(t *types.Type) int { // Sizeof(runtime.uncommontype{}) if t.Sym == nil && len(methods(t)) == 0 { @@ -1422,6 +1423,20 @@ func dtypesym(t *types.Type) *obj.LSym { return lsym } +// ifaceMethodOffset returns the offset of the i-th method in the interface +// type descriptor, ityp. +func ifaceMethodOffset(ityp *types.Type, i int64) int64 { + // interface type descriptor layout is struct { + // _type // commonSize + // pkgpath // 1 word + // []imethod // 3 words (pointing to [...]imethod below) + // uncommontype // uncommonSize + // [...]imethod + // } + // The size of imethod is 8. + return int64(commonSize()+4*Widthptr+uncommonSize(ityp)) + i*8 +} + // for each itabEntry, gather the methods on // the concrete type that implement the interface func peekitabs() { diff --git a/src/cmd/compile/internal/gc/walk.go b/src/cmd/compile/internal/gc/walk.go index d238cc2f45f..8e45059eab1 100644 --- a/src/cmd/compile/internal/gc/walk.go +++ b/src/cmd/compile/internal/gc/walk.go @@ -565,6 +565,7 @@ opswitch: case OCALLINTER, OCALLFUNC, OCALLMETH: if n.Op == OCALLINTER { usemethod(n) + markUsedIfaceMethod(n) } if n.Op == OCALLFUNC && n.Left.Op == OCLOSURE { @@ -1630,6 +1631,20 @@ func markTypeUsedInInterface(t *types.Type, from *obj.LSym) { r.Type = objabi.R_USEIFACE } +// markUsedIfaceMethod marks that an interface method is used in the current +// function. n is OCALLINTER node. +func markUsedIfaceMethod(n *Node) { + ityp := n.Left.Left.Type + tsym := typenamesym(ityp).Linksym() + r := obj.Addrel(Curfn.Func.lsym) + r.Sym = tsym + // n.Left.Xoffset is the method index * Widthptr (the offset of code pointer + // in itab). + midx := n.Left.Xoffset / int64(Widthptr) + r.Add = ifaceMethodOffset(ityp, midx) + r.Type = objabi.R_USEIFACEMETHOD +} + // rtconvfn returns the parameter and result types that will be used by a // runtime function to convert from type src to type dst. The runtime function // name can be derived from the names of the returned types. diff --git a/src/cmd/internal/objabi/reloctype.go b/src/cmd/internal/objabi/reloctype.go index 1e328d659f6..9e2e4a150ac 100644 --- a/src/cmd/internal/objabi/reloctype.go +++ b/src/cmd/internal/objabi/reloctype.go @@ -94,6 +94,12 @@ const ( // This is a marker relocation (0-sized), for the linker's reachabililty // analysis. R_USEIFACE + // R_USEIFACEMETHOD marks an interface method that is used in the function + // this relocation is applied to. The target is an interface type descriptor. + // The addend is the offset of the method in the type descriptor. + // This is a marker relocation (0-sized), for the linker's reachabililty + // analysis. + R_USEIFACEMETHOD // R_METHODOFF resolves to a 32-bit offset from the beginning of the section // holding the data being relocated to the referenced symbol. // It is a variant of R_ADDROFF used when linking from the uncommonType of a diff --git a/src/cmd/internal/objabi/reloctype_string.go b/src/cmd/internal/objabi/reloctype_string.go index caf24eea58d..01df4cce624 100644 --- a/src/cmd/internal/objabi/reloctype_string.go +++ b/src/cmd/internal/objabi/reloctype_string.go @@ -33,42 +33,43 @@ func _() { _ = x[R_USEFIELD-23] _ = x[R_USETYPE-24] _ = x[R_USEIFACE-25] - _ = x[R_METHODOFF-26] - _ = x[R_POWER_TOC-27] - _ = x[R_GOTPCREL-28] - _ = x[R_JMPMIPS-29] - _ = x[R_DWARFSECREF-30] - _ = x[R_DWARFFILEREF-31] - _ = x[R_ARM64_TLS_LE-32] - _ = x[R_ARM64_TLS_IE-33] - _ = x[R_ARM64_GOTPCREL-34] - _ = x[R_ARM64_GOT-35] - _ = x[R_ARM64_PCREL-36] - _ = x[R_ARM64_LDST8-37] - _ = x[R_ARM64_LDST32-38] - _ = x[R_ARM64_LDST64-39] - _ = x[R_ARM64_LDST128-40] - _ = x[R_POWER_TLS_LE-41] - _ = x[R_POWER_TLS_IE-42] - _ = x[R_POWER_TLS-43] - _ = x[R_ADDRPOWER_DS-44] - _ = x[R_ADDRPOWER_GOT-45] - _ = x[R_ADDRPOWER_PCREL-46] - _ = x[R_ADDRPOWER_TOCREL-47] - _ = x[R_ADDRPOWER_TOCREL_DS-48] - _ = x[R_RISCV_PCREL_ITYPE-49] - _ = x[R_RISCV_PCREL_STYPE-50] - _ = x[R_PCRELDBL-51] - _ = x[R_ADDRMIPSU-52] - _ = x[R_ADDRMIPSTLS-53] - _ = x[R_ADDRCUOFF-54] - _ = x[R_WASMIMPORT-55] - _ = x[R_XCOFFREF-56] + _ = x[R_USEIFACEMETHOD-26] + _ = x[R_METHODOFF-27] + _ = x[R_POWER_TOC-28] + _ = x[R_GOTPCREL-29] + _ = x[R_JMPMIPS-30] + _ = x[R_DWARFSECREF-31] + _ = x[R_DWARFFILEREF-32] + _ = x[R_ARM64_TLS_LE-33] + _ = x[R_ARM64_TLS_IE-34] + _ = x[R_ARM64_GOTPCREL-35] + _ = x[R_ARM64_GOT-36] + _ = x[R_ARM64_PCREL-37] + _ = x[R_ARM64_LDST8-38] + _ = x[R_ARM64_LDST32-39] + _ = x[R_ARM64_LDST64-40] + _ = x[R_ARM64_LDST128-41] + _ = x[R_POWER_TLS_LE-42] + _ = x[R_POWER_TLS_IE-43] + _ = x[R_POWER_TLS-44] + _ = x[R_ADDRPOWER_DS-45] + _ = x[R_ADDRPOWER_GOT-46] + _ = x[R_ADDRPOWER_PCREL-47] + _ = x[R_ADDRPOWER_TOCREL-48] + _ = x[R_ADDRPOWER_TOCREL_DS-49] + _ = x[R_RISCV_PCREL_ITYPE-50] + _ = x[R_RISCV_PCREL_STYPE-51] + _ = x[R_PCRELDBL-52] + _ = x[R_ADDRMIPSU-53] + _ = x[R_ADDRMIPSTLS-54] + _ = x[R_ADDRCUOFF-55] + _ = x[R_WASMIMPORT-56] + _ = x[R_XCOFFREF-57] } -const _RelocType_name = "R_ADDRR_ADDRPOWERR_ADDRARM64R_ADDRMIPSR_ADDROFFR_WEAKADDROFFR_SIZER_CALLR_CALLARMR_CALLARM64R_CALLINDR_CALLPOWERR_CALLMIPSR_CALLRISCVR_CONSTR_PCRELR_TLS_LER_TLS_IER_GOTOFFR_PLT0R_PLT1R_PLT2R_USEFIELDR_USETYPER_USEIFACER_METHODOFFR_POWER_TOCR_GOTPCRELR_JMPMIPSR_DWARFSECREFR_DWARFFILEREFR_ARM64_TLS_LER_ARM64_TLS_IER_ARM64_GOTPCRELR_ARM64_GOTR_ARM64_PCRELR_ARM64_LDST8R_ARM64_LDST32R_ARM64_LDST64R_ARM64_LDST128R_POWER_TLS_LER_POWER_TLS_IER_POWER_TLSR_ADDRPOWER_DSR_ADDRPOWER_GOTR_ADDRPOWER_PCRELR_ADDRPOWER_TOCRELR_ADDRPOWER_TOCREL_DSR_RISCV_PCREL_ITYPER_RISCV_PCREL_STYPER_PCRELDBLR_ADDRMIPSUR_ADDRMIPSTLSR_ADDRCUOFFR_WASMIMPORTR_XCOFFREF" +const _RelocType_name = "R_ADDRR_ADDRPOWERR_ADDRARM64R_ADDRMIPSR_ADDROFFR_WEAKADDROFFR_SIZER_CALLR_CALLARMR_CALLARM64R_CALLINDR_CALLPOWERR_CALLMIPSR_CALLRISCVR_CONSTR_PCRELR_TLS_LER_TLS_IER_GOTOFFR_PLT0R_PLT1R_PLT2R_USEFIELDR_USETYPER_USEIFACER_USEIFACEMETHODR_METHODOFFR_POWER_TOCR_GOTPCRELR_JMPMIPSR_DWARFSECREFR_DWARFFILEREFR_ARM64_TLS_LER_ARM64_TLS_IER_ARM64_GOTPCRELR_ARM64_GOTR_ARM64_PCRELR_ARM64_LDST8R_ARM64_LDST32R_ARM64_LDST64R_ARM64_LDST128R_POWER_TLS_LER_POWER_TLS_IER_POWER_TLSR_ADDRPOWER_DSR_ADDRPOWER_GOTR_ADDRPOWER_PCRELR_ADDRPOWER_TOCRELR_ADDRPOWER_TOCREL_DSR_RISCV_PCREL_ITYPER_RISCV_PCREL_STYPER_PCRELDBLR_ADDRMIPSUR_ADDRMIPSTLSR_ADDRCUOFFR_WASMIMPORTR_XCOFFREF" -var _RelocType_index = [...]uint16{0, 6, 17, 28, 38, 47, 60, 66, 72, 81, 92, 101, 112, 122, 133, 140, 147, 155, 163, 171, 177, 183, 189, 199, 208, 218, 229, 240, 250, 259, 272, 286, 300, 314, 330, 341, 354, 367, 381, 395, 410, 424, 438, 449, 463, 478, 495, 513, 534, 553, 572, 582, 593, 606, 617, 629, 639} +var _RelocType_index = [...]uint16{0, 6, 17, 28, 38, 47, 60, 66, 72, 81, 92, 101, 112, 122, 133, 140, 147, 155, 163, 171, 177, 183, 189, 199, 208, 218, 234, 245, 256, 266, 275, 288, 302, 316, 330, 346, 357, 370, 383, 397, 411, 426, 440, 454, 465, 479, 494, 511, 529, 550, 569, 588, 598, 609, 622, 633, 645, 655} func (i RelocType) String() string { i -= 1 diff --git a/src/cmd/link/internal/ld/deadcode.go b/src/cmd/link/internal/ld/deadcode.go index 816a23b9a71..74d61fa4951 100644 --- a/src/cmd/link/internal/ld/deadcode.go +++ b/src/cmd/link/internal/ld/deadcode.go @@ -106,25 +106,16 @@ func (d *deadcodePass) flood() { if isgotype { usedInIface = d.ldr.AttrUsedInIface(symIdx) - p := d.ldr.Data(symIdx) - if len(p) != 0 && decodetypeKind(d.ctxt.Arch, p)&kindMask == kindInterface { - for _, sig := range d.decodeIfaceMethods(d.ldr, d.ctxt.Arch, symIdx, &relocs) { - if d.ctxt.Debugvlog > 1 { - d.ctxt.Logf("reached iface method: %v\n", sig) - } - d.ifaceMethod[sig] = true - } - } } methods = methods[:0] for i := 0; i < relocs.Count(); i++ { r := relocs.At(i) t := r.Type() - if t == objabi.R_WEAKADDROFF { + switch t { + case objabi.R_WEAKADDROFF: continue - } - if t == objabi.R_METHODOFF { + case objabi.R_METHODOFF: if i+2 >= relocs.Count() { panic("expect three consecutive R_METHODOFF relocs") } @@ -146,14 +137,12 @@ func (d *deadcodePass) flood() { } i += 2 continue - } - if t == objabi.R_USETYPE { + case objabi.R_USETYPE: // type symbol used for DWARF. we need to load the symbol but it may not // be otherwise reachable in the program. // do nothing for now as we still load all type symbols. continue - } - if t == objabi.R_USEIFACE { + case objabi.R_USEIFACE: // R_USEIFACE is a marker relocation that tells the linker the type is // converted to an interface, i.e. should have UsedInIface set. See the // comment below for why we need to unset the Reachable bit and re-mark it. @@ -166,6 +155,18 @@ func (d *deadcodePass) flood() { } } continue + case objabi.R_USEIFACEMETHOD: + // R_USEIFACEMETHOD is a marker relocation that marks an interface + // method as used. + rs := r.Sym() + if d.ldr.SymType(rs) != sym.SDYNIMPORT { // don't decode DYNIMPORT symbol (we'll mark all exported methods anyway) + m := d.decodeIfaceMethod(d.ldr, d.ctxt.Arch, rs, r.Add()) + if d.ctxt.Debugvlog > 1 { + d.ctxt.Logf("reached iface method: %v\n", m) + } + d.ifaceMethod[m] = true + } + continue } rs := r.Sym() if isgotype && usedInIface && d.ldr.IsGoType(rs) && !d.ldr.AttrUsedInIface(rs) { @@ -378,23 +379,17 @@ func (d *deadcodePass) decodeMethodSig(ldr *loader.Loader, arch *sys.Arch, symId return methods } -func (d *deadcodePass) decodeIfaceMethods(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, relocs *loader.Relocs) []methodsig { +// Decode the method of interface type symbol symIdx at offset off. +func (d *deadcodePass) decodeIfaceMethod(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, off int64) methodsig { p := ldr.Data(symIdx) if decodetypeKind(arch, p)&kindMask != kindInterface { panic(fmt.Sprintf("symbol %q is not an interface", ldr.SymName(symIdx))) } - rel := decodeReloc(ldr, symIdx, relocs, int32(commonsize(arch)+arch.PtrSize)) - s := rel.Sym() - if s == 0 { - return nil - } - if s != symIdx { - panic(fmt.Sprintf("imethod slice pointer in %q leads to a different symbol", ldr.SymName(symIdx))) - } - off := int(rel.Add()) // array of reflect.imethod values - numMethods := int(decodetypeIfaceMethodCount(arch, p)) - sizeofIMethod := 4 + 4 - return d.decodeMethodSig(ldr, arch, symIdx, relocs, off, sizeofIMethod, numMethods) + relocs := ldr.Relocs(symIdx) + var m methodsig + m.name = decodetypeName(ldr, symIdx, &relocs, int(off)) + m.typ = decodeRelocSym(ldr, symIdx, &relocs, int32(off+4)) + return m } func (d *deadcodePass) decodetypeMethods(ldr *loader.Loader, arch *sys.Arch, symIdx loader.Sym, relocs *loader.Relocs) []methodsig { diff --git a/src/cmd/link/internal/ld/deadcode_test.go b/src/cmd/link/internal/ld/deadcode_test.go index ab836dc8f89..b756091613c 100644 --- a/src/cmd/link/internal/ld/deadcode_test.go +++ b/src/cmd/link/internal/ld/deadcode_test.go @@ -33,6 +33,7 @@ func TestDeadcode(t *testing.T) { {"ifacemethod", "", "main.T.M"}, {"ifacemethod2", "main.T.M", ""}, {"ifacemethod3", "main.S.M", ""}, + {"ifacemethod4", "", "main.T.M"}, } for _, test := range tests { test := test diff --git a/src/cmd/link/internal/ld/testdata/deadcode/ifacemethod4.go b/src/cmd/link/internal/ld/testdata/deadcode/ifacemethod4.go new file mode 100644 index 00000000000..52ee2e3d860 --- /dev/null +++ b/src/cmd/link/internal/ld/testdata/deadcode/ifacemethod4.go @@ -0,0 +1,23 @@ +// Copyright 2020 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. + +// Test that a live type's method is not live even if +// it matches an interface method, as long as the interface +// method is not used. + +package main + +type T int + +func (T) M() {} + +type I interface{ M() } + +var p *T +var pp *I + +func main() { + p = new(T) // use type T + pp = new(I) // use type I +}