/
alg.go
562 lines (472 loc) · 12.2 KB
/
alg.go
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// Copyright 2016 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 gc
import (
"cmd/compile/internal/types"
"fmt"
)
// AlgKind describes the kind of algorithms used for comparing and
// hashing a Type.
type AlgKind int
const (
// These values are known by runtime.
ANOEQ AlgKind = iota
AMEM0
AMEM8
AMEM16
AMEM32
AMEM64
AMEM128
ASTRING
AINTER
ANILINTER
AFLOAT32
AFLOAT64
ACPLX64
ACPLX128
// Type can be compared/hashed as regular memory.
AMEM AlgKind = 100
// Type needs special comparison/hashing functions.
ASPECIAL AlgKind = -1
)
// IsComparable reports whether t is a comparable type.
func IsComparable(t *types.Type) bool {
a, _ := algtype1(t)
return a != ANOEQ
}
// IsRegularMemory reports whether t can be compared/hashed as regular memory.
func IsRegularMemory(t *types.Type) bool {
a, _ := algtype1(t)
return a == AMEM
}
// IncomparableField returns an incomparable Field of struct Type t, if any.
func IncomparableField(t *types.Type) *types.Field {
for _, f := range t.FieldSlice() {
if !IsComparable(f.Type) {
return f
}
}
return nil
}
// algtype is like algtype1, except it returns the fixed-width AMEMxx variants
// instead of the general AMEM kind when possible.
func algtype(t *types.Type) AlgKind {
a, _ := algtype1(t)
if a == AMEM {
switch t.Width {
case 0:
return AMEM0
case 1:
return AMEM8
case 2:
return AMEM16
case 4:
return AMEM32
case 8:
return AMEM64
case 16:
return AMEM128
}
}
return a
}
// algtype1 returns the AlgKind used for comparing and hashing Type t.
// If it returns ANOEQ, it also returns the component type of t that
// makes it incomparable.
func algtype1(t *types.Type) (AlgKind, *types.Type) {
if t.Broke() {
return AMEM, nil
}
if t.Noalg() {
return ANOEQ, t
}
switch t.Etype {
case TANY, TFORW:
// will be defined later.
return ANOEQ, t
case TINT8, TUINT8, TINT16, TUINT16,
TINT32, TUINT32, TINT64, TUINT64,
TINT, TUINT, TUINTPTR,
TBOOL, TPTR,
TCHAN, TUNSAFEPTR:
return AMEM, nil
case TFUNC, TMAP:
return ANOEQ, t
case TFLOAT32:
return AFLOAT32, nil
case TFLOAT64:
return AFLOAT64, nil
case TCOMPLEX64:
return ACPLX64, nil
case TCOMPLEX128:
return ACPLX128, nil
case TSTRING:
return ASTRING, nil
case TINTER:
if t.IsEmptyInterface() {
return ANILINTER, nil
}
return AINTER, nil
case TSLICE:
return ANOEQ, t
case TARRAY:
a, bad := algtype1(t.Elem())
switch a {
case AMEM:
return AMEM, nil
case ANOEQ:
return ANOEQ, bad
}
switch t.NumElem() {
case 0:
// We checked above that the element type is comparable.
return AMEM, nil
case 1:
// Single-element array is same as its lone element.
return a, nil
}
return ASPECIAL, nil
case TSTRUCT:
fields := t.FieldSlice()
// One-field struct is same as that one field alone.
if len(fields) == 1 && !fields[0].Sym.IsBlank() {
return algtype1(fields[0].Type)
}
ret := AMEM
for i, f := range fields {
// All fields must be comparable.
a, bad := algtype1(f.Type)
if a == ANOEQ {
return ANOEQ, bad
}
// Blank fields, padded fields, fields with non-memory
// equality need special compare.
if a != AMEM || f.Sym.IsBlank() || ispaddedfield(t, i) {
ret = ASPECIAL
}
}
return ret, nil
}
Fatalf("algtype1: unexpected type %v", t)
return 0, nil
}
// Generate a helper function to compute the hash of a value of type t.
func genhash(sym *types.Sym, t *types.Type) {
if Debug['r'] != 0 {
fmt.Printf("genhash %v %v\n", sym, t)
}
lineno = autogeneratedPos // less confusing than end of input
dclcontext = PEXTERN
// func sym(p *T, h uintptr) uintptr
tfn := nod(OTFUNC, nil, nil)
tfn.List.Set2(
namedfield("p", types.NewPtr(t)),
namedfield("h", types.Types[TUINTPTR]),
)
tfn.Rlist.Set1(anonfield(types.Types[TUINTPTR]))
fn := dclfunc(sym, tfn)
np := asNode(tfn.Type.Params().Field(0).Nname)
nh := asNode(tfn.Type.Params().Field(1).Nname)
// genhash is only called for types that have equality but
// cannot be handled by the standard algorithms,
// so t must be either an array or a struct.
switch t.Etype {
default:
Fatalf("genhash %v", t)
case types.TARRAY:
// An array of pure memory would be handled by the
// standard algorithm, so the element type must not be
// pure memory.
hashel := hashfor(t.Elem())
n := nod(ORANGE, nil, nod(ODEREF, np, nil))
ni := newname(lookup("i"))
ni.Type = types.Types[TINT]
n.List.Set1(ni)
n.SetColas(true)
colasdefn(n.List.Slice(), n)
ni = n.List.First()
// h = hashel(&p[i], h)
call := nod(OCALL, hashel, nil)
nx := nod(OINDEX, np, ni)
nx.SetBounded(true)
na := nod(OADDR, nx, nil)
call.List.Append(na)
call.List.Append(nh)
n.Nbody.Append(nod(OAS, nh, call))
fn.Nbody.Append(n)
case types.TSTRUCT:
// Walk the struct using memhash for runs of AMEM
// and calling specific hash functions for the others.
for i, fields := 0, t.FieldSlice(); i < len(fields); {
f := fields[i]
// Skip blank fields.
if f.Sym.IsBlank() {
i++
continue
}
// Hash non-memory fields with appropriate hash function.
if !IsRegularMemory(f.Type) {
hashel := hashfor(f.Type)
call := nod(OCALL, hashel, nil)
nx := nodSym(OXDOT, np, f.Sym) // TODO: fields from other packages?
na := nod(OADDR, nx, nil)
call.List.Append(na)
call.List.Append(nh)
fn.Nbody.Append(nod(OAS, nh, call))
i++
continue
}
// Otherwise, hash a maximal length run of raw memory.
size, next := memrun(t, i)
// h = hashel(&p.first, size, h)
hashel := hashmem(f.Type)
call := nod(OCALL, hashel, nil)
nx := nodSym(OXDOT, np, f.Sym) // TODO: fields from other packages?
na := nod(OADDR, nx, nil)
call.List.Append(na)
call.List.Append(nh)
call.List.Append(nodintconst(size))
fn.Nbody.Append(nod(OAS, nh, call))
i = next
}
}
r := nod(ORETURN, nil, nil)
r.List.Append(nh)
fn.Nbody.Append(r)
if Debug['r'] != 0 {
dumplist("genhash body", fn.Nbody)
}
funcbody()
fn.Func.SetDupok(true)
fn = typecheck(fn, ctxStmt)
Curfn = fn
typecheckslice(fn.Nbody.Slice(), ctxStmt)
Curfn = nil
if debug_dclstack != 0 {
testdclstack()
}
fn.Func.SetNilCheckDisabled(true)
funccompile(fn)
}
func hashfor(t *types.Type) *Node {
var sym *types.Sym
switch a, _ := algtype1(t); a {
case AMEM:
Fatalf("hashfor with AMEM type")
case AINTER:
sym = Runtimepkg.Lookup("interhash")
case ANILINTER:
sym = Runtimepkg.Lookup("nilinterhash")
case ASTRING:
sym = Runtimepkg.Lookup("strhash")
case AFLOAT32:
sym = Runtimepkg.Lookup("f32hash")
case AFLOAT64:
sym = Runtimepkg.Lookup("f64hash")
case ACPLX64:
sym = Runtimepkg.Lookup("c64hash")
case ACPLX128:
sym = Runtimepkg.Lookup("c128hash")
default:
sym = typesymprefix(".hash", t)
}
n := newname(sym)
n.SetClass(PFUNC)
n.Sym.SetFunc(true)
n.Type = functype(nil, []*Node{
anonfield(types.NewPtr(t)),
anonfield(types.Types[TUINTPTR]),
}, []*Node{
anonfield(types.Types[TUINTPTR]),
})
return n
}
// geneq generates a helper function to
// check equality of two values of type t.
func geneq(sym *types.Sym, t *types.Type) {
if Debug['r'] != 0 {
fmt.Printf("geneq %v %v\n", sym, t)
}
lineno = autogeneratedPos // less confusing than end of input
dclcontext = PEXTERN
// func sym(p, q *T) bool
tfn := nod(OTFUNC, nil, nil)
tfn.List.Set2(
namedfield("p", types.NewPtr(t)),
namedfield("q", types.NewPtr(t)),
)
tfn.Rlist.Set1(anonfield(types.Types[TBOOL]))
fn := dclfunc(sym, tfn)
np := asNode(tfn.Type.Params().Field(0).Nname)
nq := asNode(tfn.Type.Params().Field(1).Nname)
// geneq is only called for types that have equality but
// cannot be handled by the standard algorithms,
// so t must be either an array or a struct.
switch t.Etype {
default:
Fatalf("geneq %v", t)
case TARRAY:
// An array of pure memory would be handled by the
// standard memequal, so the element type must not be
// pure memory. Even if we unrolled the range loop,
// each iteration would be a function call, so don't bother
// unrolling.
nrange := nod(ORANGE, nil, nod(ODEREF, np, nil))
ni := newname(lookup("i"))
ni.Type = types.Types[TINT]
nrange.List.Set1(ni)
nrange.SetColas(true)
colasdefn(nrange.List.Slice(), nrange)
ni = nrange.List.First()
// if p[i] != q[i] { return false }
nx := nod(OINDEX, np, ni)
nx.SetBounded(true)
ny := nod(OINDEX, nq, ni)
ny.SetBounded(true)
nif := nod(OIF, nil, nil)
nif.Left = nod(ONE, nx, ny)
r := nod(ORETURN, nil, nil)
r.List.Append(nodbool(false))
nif.Nbody.Append(r)
nrange.Nbody.Append(nif)
fn.Nbody.Append(nrange)
// return true
ret := nod(ORETURN, nil, nil)
ret.List.Append(nodbool(true))
fn.Nbody.Append(ret)
case TSTRUCT:
var cond *Node
and := func(n *Node) {
if cond == nil {
cond = n
return
}
cond = nod(OANDAND, cond, n)
}
// Walk the struct using memequal for runs of AMEM
// and calling specific equality tests for the others.
for i, fields := 0, t.FieldSlice(); i < len(fields); {
f := fields[i]
// Skip blank-named fields.
if f.Sym.IsBlank() {
i++
continue
}
// Compare non-memory fields with field equality.
if !IsRegularMemory(f.Type) {
and(eqfield(np, nq, f.Sym))
i++
continue
}
// Find maximal length run of memory-only fields.
size, next := memrun(t, i)
// TODO(rsc): All the calls to newname are wrong for
// cross-package unexported fields.
if s := fields[i:next]; len(s) <= 2 {
// Two or fewer fields: use plain field equality.
for _, f := range s {
and(eqfield(np, nq, f.Sym))
}
} else {
// More than two fields: use memequal.
and(eqmem(np, nq, f.Sym, size))
}
i = next
}
if cond == nil {
cond = nodbool(true)
}
ret := nod(ORETURN, nil, nil)
ret.List.Append(cond)
fn.Nbody.Append(ret)
}
if Debug['r'] != 0 {
dumplist("geneq body", fn.Nbody)
}
funcbody()
fn.Func.SetDupok(true)
fn = typecheck(fn, ctxStmt)
Curfn = fn
typecheckslice(fn.Nbody.Slice(), ctxStmt)
Curfn = nil
if debug_dclstack != 0 {
testdclstack()
}
// Disable checknils while compiling this code.
// We are comparing a struct or an array,
// neither of which can be nil, and our comparisons
// are shallow.
fn.Func.SetNilCheckDisabled(true)
funccompile(fn)
}
// eqfield returns the node
// p.field == q.field
func eqfield(p *Node, q *Node, field *types.Sym) *Node {
nx := nodSym(OXDOT, p, field)
ny := nodSym(OXDOT, q, field)
ne := nod(OEQ, nx, ny)
return ne
}
// eqmem returns the node
// memequal(&p.field, &q.field [, size])
func eqmem(p *Node, q *Node, field *types.Sym, size int64) *Node {
nx := nod(OADDR, nodSym(OXDOT, p, field), nil)
ny := nod(OADDR, nodSym(OXDOT, q, field), nil)
nx = typecheck(nx, ctxExpr)
ny = typecheck(ny, ctxExpr)
fn, needsize := eqmemfunc(size, nx.Type.Elem())
call := nod(OCALL, fn, nil)
call.List.Append(nx)
call.List.Append(ny)
if needsize {
call.List.Append(nodintconst(size))
}
return call
}
func eqmemfunc(size int64, t *types.Type) (fn *Node, needsize bool) {
switch size {
default:
fn = syslook("memequal")
needsize = true
case 1, 2, 4, 8, 16:
buf := fmt.Sprintf("memequal%d", int(size)*8)
fn = syslook(buf)
}
fn = substArgTypes(fn, t, t)
return fn, needsize
}
// memrun finds runs of struct fields for which memory-only algs are appropriate.
// t is the parent struct type, and start is the field index at which to start the run.
// size is the length in bytes of the memory included in the run.
// next is the index just after the end of the memory run.
func memrun(t *types.Type, start int) (size int64, next int) {
next = start
for {
next++
if next == t.NumFields() {
break
}
// Stop run after a padded field.
if ispaddedfield(t, next-1) {
break
}
// Also, stop before a blank or non-memory field.
if f := t.Field(next); f.Sym.IsBlank() || !IsRegularMemory(f.Type) {
break
}
}
return t.Field(next-1).End() - t.Field(start).Offset, next
}
// ispaddedfield reports whether the i'th field of struct type t is followed
// by padding.
func ispaddedfield(t *types.Type, i int) bool {
if !t.IsStruct() {
Fatalf("ispaddedfield called non-struct %v", t)
}
end := t.Width
if i+1 < t.NumFields() {
end = t.Field(i + 1).Offset
}
return t.Field(i).End() != end
}