mirror of
https://github.com/golang/go
synced 2024-11-12 09:20:22 -07:00
exp/ssa: special-case 'range' loops based on type of range expression.
The lowering of ast.RangeStmt now has three distinct cases: 1) rangeIter for maps and strings; approximately: it = range x for { k, v, ok = next it if !ok { break } ... } The Range instruction and the interpreter's "iter" datatype are now restricted to these types. 2) rangeChan for channels; approximately: for { k, ok = <-x if !ok { break } ... } 3) rangeIndexed for slices, arrays, and *array; approximately: for k, l = 0, len(x); k < l; k++ { v = x[k] ... } In all cases we now evaluate the side effects of the range expression exactly once, per comments on http://code.google.com/p/go/issues/detail?id=4644. However the exact spec wording is still being discussed in https://golang.org/cl/7307083/. Further (small) changes may be required once the dust settles. R=iant CC=golang-dev https://golang.org/cl/7303074
This commit is contained in:
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1c1096ea31
commit
d8e3b16f8b
@ -1949,49 +1949,196 @@ func (b *Builder) forStmt(fn *Function, s *ast.ForStmt, label *lblock) {
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fn.currentBlock = done
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}
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// rangeIndexed emits to fn the header for an integer indexed loop
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// over array, *array or slice value x.
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// The v result is defined only if tv is non-nil.
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//
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func (b *Builder) rangeIndexed(fn *Function, x Value, tv types.Type) (k, v Value, loop, done *BasicBlock) {
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//
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// length = len(x)
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// index = -1
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// loop: (target of continue)
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// index++
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// if index < length goto body else done
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// body:
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// k = index
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// v = x[index]
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// ...body...
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// jump loop
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// done: (target of break)
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// Determine number of iterations.
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var length Value
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if arr, ok := deref(x.Type()).(*types.Array); ok {
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// For array or *array, the number of iterations is
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// known statically thanks to the type. We avoid a
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// data dependence upon x, permitting later dead-code
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// elimination if x is pure, static unrolling, etc.
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// Ranging over a nil *array may have >0 iterations.
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length = intLiteral(arr.Len)
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} else {
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// length = len(x).
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var call Call
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call.Func = b.globals[types.Universe.Lookup("len")]
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call.Args = []Value{x}
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call.setType(tInt)
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length = fn.emit(&call)
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}
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index := fn.addLocal(tInt)
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emitStore(fn, index, intLiteral(-1))
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loop = fn.newBasicBlock("rangeindex.loop")
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emitJump(fn, loop)
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fn.currentBlock = loop
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incr := &BinOp{
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Op: token.ADD,
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X: emitLoad(fn, index),
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Y: intLiteral(1),
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}
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incr.setType(tInt)
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emitStore(fn, index, fn.emit(incr))
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body := fn.newBasicBlock("rangeindex.body")
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done = fn.newBasicBlock("rangeindex.done")
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emitIf(fn, emitCompare(fn, token.LSS, incr, length), body, done)
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fn.currentBlock = body
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k = emitLoad(fn, index)
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if tv != nil {
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switch t := underlyingType(x.Type()).(type) {
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case *types.Array:
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instr := &Index{
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X: x,
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Index: k,
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}
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instr.setType(t.Elt)
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v = fn.emit(instr)
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case *types.Pointer: // *array
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instr := &IndexAddr{
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X: x,
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Index: k,
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}
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instr.setType(pointer(t.Base.(*types.Array).Elt))
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v = emitLoad(fn, fn.emit(instr))
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case *types.Slice:
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instr := &IndexAddr{
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X: x,
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Index: k,
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}
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instr.setType(pointer(t.Elt))
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v = emitLoad(fn, fn.emit(instr))
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default:
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panic("rangeIndexed x:" + t.String())
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}
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}
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return
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}
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// rangeIter emits to fn the header for a loop using
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// Range/Next/Extract to iterate over map or string value x.
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// tk and tv are the types of the key/value results k and v, or nil
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// if the respective component is not wanted.
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//
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func (b *Builder) rangeIter(fn *Function, x Value, tk, tv types.Type) (k, v Value, loop, done *BasicBlock) {
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//
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// it = range x
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// loop: (target of continue)
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// okv = next it (ok, key, value)
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// ok = extract okv #0
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// if ok goto body else done
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// body:
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// k = extract okv #1
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// v = extract okv #2
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// ...body...
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// jump loop
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// done: (target of break)
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//
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rng := &Range{X: x}
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rng.setType(tRangeIter)
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it := fn.emit(rng)
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loop = fn.newBasicBlock("rangeiter.loop")
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emitJump(fn, loop)
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fn.currentBlock = loop
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okv := &Next{Iter: it}
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okv.setType(&types.Result{Values: []*types.Var{
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varOk,
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{Name: "k", Type: tk},
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{Name: "v", Type: tv},
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}})
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fn.emit(okv)
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body := fn.newBasicBlock("rangeiter.body")
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done = fn.newBasicBlock("rangeiter.done")
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emitIf(fn, emitExtract(fn, okv, 0, tBool), body, done)
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fn.currentBlock = body
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if tk != nil {
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k = emitExtract(fn, okv, 1, tk)
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}
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if tv != nil {
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v = emitExtract(fn, okv, 2, tv)
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}
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return
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}
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// rangeChan emits to fn the header for a loop that receives from
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// channel x until it fails.
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// tk is the channel's element type, or nil if the k result is not
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// wanted
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//
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func (b *Builder) rangeChan(fn *Function, x Value, tk types.Type) (k Value, loop, done *BasicBlock) {
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//
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// loop: (target of continue)
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// ko = <-x (key, ok)
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// ok = extract ko #1
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// if ok goto body else done
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// body:
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// k = extract ko #0
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// ...
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// goto loop
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// done: (target of break)
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loop = fn.newBasicBlock("rangechan.loop")
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emitJump(fn, loop)
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fn.currentBlock = loop
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recv := &UnOp{
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Op: token.ARROW,
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X: x,
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CommaOk: true,
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}
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recv.setType(&types.Result{Values: []*types.Var{
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{Name: "k", Type: tk},
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varOk,
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}})
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ko := fn.emit(recv)
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body := fn.newBasicBlock("rangechan.body")
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done = fn.newBasicBlock("rangechan.done")
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emitIf(fn, emitExtract(fn, ko, 1, tBool), body, done)
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fn.currentBlock = body
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if tk != nil {
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k = emitExtract(fn, ko, 0, tk)
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}
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return
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}
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// rangeStmt emits to fn code for the range statement s, optionally
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// labelled by label.
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//
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func (b *Builder) rangeStmt(fn *Function, s *ast.RangeStmt, label *lblock) {
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// it := range x
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// jump loop
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// loop: (target of continue)
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// okv := next it (ok, key, value?)
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// ok = extract okv #0
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// if ok goto body else done
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// body:
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// t0 = extract okv #1
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// k = *t0
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// t1 = extract okv #2
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// v = *t1
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// ...body...
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// jump loop
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// done: (target of break)
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hasK := !isBlankIdent(s.Key)
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hasV := s.Value != nil && !isBlankIdent(s.Value)
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// Ranging over just the keys of a pointer to an array
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// doesn't (need to) evaluate the array:
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// for i := range (*[10]int)(nil) {...}
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// Instead it is transformed into a simple loop:
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// i = -1
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// jump loop
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// loop: (target of continue)
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// increment i
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// if i < 10 goto body else done
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// body:
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// k = i
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// ...body...
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// jump loop
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// done: (target of break)
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var arrayLen int64 = -1
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if !hasV {
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if ptr, ok := underlyingType(b.exprType(s.X)).(*types.Pointer); ok {
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if arr, ok := underlyingType(ptr.Base).(*types.Array); ok {
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arrayLen = arr.Len
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}
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}
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var tk, tv types.Type
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if !isBlankIdent(s.Key) {
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tk = b.exprType(s.Key)
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}
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if s.Value != nil && !isBlankIdent(s.Value) {
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tv = b.exprType(s.Value)
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}
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// If iteration variables are defined (:=), this
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@ -2001,91 +2148,52 @@ func (b *Builder) rangeStmt(fn *Function, s *ast.RangeStmt, label *lblock) {
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// using := never redeclares an existing variable; it
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// always creates a new one.
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if s.Tok == token.DEFINE {
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if hasK {
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if tk != nil {
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fn.addNamedLocal(b.obj(s.Key.(*ast.Ident)))
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}
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if hasV {
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if tv != nil {
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fn.addNamedLocal(b.obj(s.Value.(*ast.Ident)))
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}
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}
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var ok Value
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var okv *Next
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var okvVars []*types.Var
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var index *Alloc // *array index loops only
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loop := fn.newBasicBlock("range.loop")
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var body, done *BasicBlock
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if arrayLen == -1 {
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rng := &Range{X: b.expr(fn, s.X)}
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rng.setType(tRangeIter)
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it := fn.emit(rng)
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x := b.expr(fn, s.X)
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emitJump(fn, loop)
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fn.currentBlock = loop
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var k, v Value
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var loop, done *BasicBlock
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switch rt := underlyingType(x.Type()).(type) {
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case *types.Slice, *types.Array, *types.Pointer: // *array
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k, v, loop, done = b.rangeIndexed(fn, x, tv)
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okv = &Next{Iter: it}
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okvVars = []*types.Var{
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varOk,
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{Name: "k", Type: tInvalid}, // mutated below
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{Name: "v", Type: tInvalid}, // mutated below
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}
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okv.setType(&types.Result{Values: okvVars})
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fn.emit(okv)
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ok = emitExtract(fn, okv, 0, tBool)
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} else {
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index = fn.addLocal(tInt)
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emitStore(fn, index, intLiteral(-1))
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case *types.Chan:
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k, loop, done = b.rangeChan(fn, x, tk)
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emitJump(fn, loop)
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fn.currentBlock = loop
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case *types.Map, *types.Basic: // string
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k, v, loop, done = b.rangeIter(fn, x, tk, tv)
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// TODO use emitArith here and elsewhere?
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incr := &BinOp{
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Op: token.ADD,
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X: emitLoad(fn, index),
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Y: intLiteral(1),
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}
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incr.setType(tInt)
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emitStore(fn, index, fn.emit(incr))
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ok = emitCompare(fn, token.LSS, incr, intLiteral(arrayLen))
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default:
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panic("Cannot range over: " + rt.String())
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}
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body = fn.newBasicBlock("range.body")
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done = fn.newBasicBlock("range.done")
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emitIf(fn, ok, body, done)
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fn.currentBlock = body
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// Evaluate both LHS expressions before we update either.
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var kl, vl lvalue
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if tk != nil {
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kl = b.addr(fn, s.Key, false) // non-escaping
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}
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if tv != nil {
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vl = b.addr(fn, s.Value, false) // non-escaping
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}
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if tk != nil {
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kl.store(fn, k)
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}
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if tv != nil {
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vl.store(fn, v)
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}
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if label != nil {
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label._break = done
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label._continue = loop
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}
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if arrayLen == -1 {
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// Evaluate both LHS expressions before we update either.
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var k, v lvalue
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if hasK {
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k = b.addr(fn, s.Key, false) // non-escaping
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okvVars[1].Type = b.exprType(s.Key)
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}
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if hasV {
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v = b.addr(fn, s.Value, false) // non-escaping
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okvVars[2].Type = b.exprType(s.Value)
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}
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if hasK {
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k.store(fn, emitExtract(fn, okv, 1, okvVars[1].Type))
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}
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if hasV {
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v.store(fn, emitExtract(fn, okv, 2, okvVars[2].Type))
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}
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} else {
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// Store a copy of the index variable to k.
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if hasK {
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k := b.addr(fn, s.Key, false) // non-escaping
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k.store(fn, emitLoad(fn, index))
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}
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}
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fn.targets = &targets{
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tail: fn.targets,
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_break: done,
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@ -1009,8 +1009,6 @@ func callBuiltin(caller *frame, callpos token.Pos, fn *ssa.Builtin, args []value
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func rangeIter(x value, t types.Type) iter {
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switch x := x.(type) {
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case nil:
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panic("range of nil")
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case map[value]value:
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// TODO(adonovan): fix: leaks goroutines and channels
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// on each incomplete map iteration. We need to open
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@ -1040,16 +1038,8 @@ func rangeIter(x value, t types.Type) iter {
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close(it)
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}()
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return it
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case *value: // non-nil *array
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return &arrayIter{a: (*x).(array)}
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case array:
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return &arrayIter{a: x}
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case []value:
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return &arrayIter{a: array(x)}
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case string:
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return &stringIter{Reader: strings.NewReader(x)}
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case chan value:
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return chanIter(x)
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}
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panic(fmt.Sprintf("cannot range over %T", x))
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}
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@ -20,7 +20,7 @@ package interp
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// *ssa.Builtin } --- functions.
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// *closure /
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// - tuple --- as returned by Ret, Next, "value,ok" modes, etc.
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// - iter --- iterators from 'range'.
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// - iter --- iterators from 'range' over map or string.
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// - bad --- a poison pill for locals that have gone out of scope.
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// - rtype -- the interpreter's concrete implementation of reflect.Type
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//
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@ -441,31 +441,6 @@ func toString(v value) string {
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// ------------------------------------------------------------------------
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// Iterators
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type arrayIter struct {
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a array
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i int
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}
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func (it *arrayIter) next() tuple {
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okv := make(tuple, 3)
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ok := it.i < len(it.a)
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okv[0] = ok
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if ok {
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okv[1] = it.i
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okv[2] = copyVal(it.a[it.i])
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}
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it.i++
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return okv
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}
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type chanIter chan value
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func (it chanIter) next() tuple {
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okv := make(tuple, 3)
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okv[1], okv[0] = <-it
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return okv
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}
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type stringIter struct {
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*strings.Reader
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i int
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@ -675,7 +675,9 @@ type Select struct {
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Blocking bool
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}
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// Range yields an iterator over the domain and range of X.
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// Range yields an iterator over the domain and range of X,
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// which must be a string or map.
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//
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// Elements are accessed via Next.
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//
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// Type() returns a *types.Result (tuple type).
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@ -685,7 +687,7 @@ type Select struct {
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//
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type Range struct {
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Register
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X Value // array, *array, slice, string, map or chan
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X Value // string or map
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}
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// Next reads and advances the iterator Iter and returns a 3-tuple
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