476 lines
12 KiB
Go
476 lines
12 KiB
Go
// Copyright 2013 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build go1.5
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package ssa
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// Helpers for emitting SSA instructions.
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import (
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"fmt"
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"go/ast"
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"go/token"
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"go/types"
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)
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// emitNew emits to f a new (heap Alloc) instruction allocating an
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// object of type typ. pos is the optional source location.
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//
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func emitNew(f *Function, typ types.Type, pos token.Pos) *Alloc {
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v := &Alloc{Heap: true}
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v.setType(types.NewPointer(typ))
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v.setPos(pos)
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f.emit(v)
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return v
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}
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// emitLoad emits to f an instruction to load the address addr into a
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// new temporary, and returns the value so defined.
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//
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func emitLoad(f *Function, addr Value) *UnOp {
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v := &UnOp{Op: token.MUL, X: addr}
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v.setType(deref(addr.Type()))
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f.emit(v)
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return v
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}
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// emitDebugRef emits to f a DebugRef pseudo-instruction associating
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// expression e with value v.
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//
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func emitDebugRef(f *Function, e ast.Expr, v Value, isAddr bool) {
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if !f.debugInfo() {
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return // debugging not enabled
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}
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if v == nil || e == nil {
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panic("nil")
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}
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var obj types.Object
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e = unparen(e)
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if id, ok := e.(*ast.Ident); ok {
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if isBlankIdent(id) {
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return
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}
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obj = f.Pkg.objectOf(id)
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switch obj.(type) {
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case *types.Nil, *types.Const, *types.Builtin:
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return
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}
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}
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f.emit(&DebugRef{
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X: v,
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Expr: e,
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IsAddr: isAddr,
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object: obj,
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})
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}
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// emitArith emits to f code to compute the binary operation op(x, y)
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// where op is an eager shift, logical or arithmetic operation.
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// (Use emitCompare() for comparisons and Builder.logicalBinop() for
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// non-eager operations.)
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//
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func emitArith(f *Function, op token.Token, x, y Value, t types.Type, pos token.Pos) Value {
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switch op {
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case token.SHL, token.SHR:
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x = emitConv(f, x, t)
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// y may be signed or an 'untyped' constant.
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// TODO(adonovan): whence signed values?
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if b, ok := y.Type().Underlying().(*types.Basic); ok && b.Info()&types.IsUnsigned == 0 {
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y = emitConv(f, y, types.Typ[types.Uint64])
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}
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case token.ADD, token.SUB, token.MUL, token.QUO, token.REM, token.AND, token.OR, token.XOR, token.AND_NOT:
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x = emitConv(f, x, t)
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y = emitConv(f, y, t)
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default:
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panic("illegal op in emitArith: " + op.String())
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}
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v := &BinOp{
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Op: op,
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X: x,
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Y: y,
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}
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v.setPos(pos)
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v.setType(t)
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return f.emit(v)
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}
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// emitCompare emits to f code compute the boolean result of
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// comparison comparison 'x op y'.
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//
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func emitCompare(f *Function, op token.Token, x, y Value, pos token.Pos) Value {
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xt := x.Type().Underlying()
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yt := y.Type().Underlying()
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// Special case to optimise a tagless SwitchStmt so that
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// these are equivalent
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// switch { case e: ...}
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// switch true { case e: ... }
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// if e==true { ... }
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// even in the case when e's type is an interface.
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// TODO(adonovan): opt: generalise to x==true, false!=y, etc.
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if x == vTrue && op == token.EQL {
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if yt, ok := yt.(*types.Basic); ok && yt.Info()&types.IsBoolean != 0 {
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return y
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}
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}
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if types.Identical(xt, yt) {
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// no conversion necessary
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} else if _, ok := xt.(*types.Interface); ok {
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y = emitConv(f, y, x.Type())
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} else if _, ok := yt.(*types.Interface); ok {
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x = emitConv(f, x, y.Type())
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} else if _, ok := x.(*Const); ok {
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x = emitConv(f, x, y.Type())
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} else if _, ok := y.(*Const); ok {
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y = emitConv(f, y, x.Type())
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} else {
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// other cases, e.g. channels. No-op.
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}
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v := &BinOp{
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Op: op,
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X: x,
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Y: y,
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}
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v.setPos(pos)
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v.setType(tBool)
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return f.emit(v)
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}
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// isValuePreserving returns true if a conversion from ut_src to
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// ut_dst is value-preserving, i.e. just a change of type.
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// Precondition: neither argument is a named type.
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//
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func isValuePreserving(ut_src, ut_dst types.Type) bool {
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// Identical underlying types?
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if structTypesIdentical(ut_dst, ut_src) {
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return true
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}
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switch ut_dst.(type) {
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case *types.Chan:
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// Conversion between channel types?
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_, ok := ut_src.(*types.Chan)
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return ok
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case *types.Pointer:
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// Conversion between pointers with identical base types?
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_, ok := ut_src.(*types.Pointer)
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return ok
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}
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return false
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}
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// emitConv emits to f code to convert Value val to exactly type typ,
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// and returns the converted value. Implicit conversions are required
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// by language assignability rules in assignments, parameter passing,
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// etc. Conversions cannot fail dynamically.
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//
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func emitConv(f *Function, val Value, typ types.Type) Value {
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t_src := val.Type()
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// Identical types? Conversion is a no-op.
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if types.Identical(t_src, typ) {
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return val
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}
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ut_dst := typ.Underlying()
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ut_src := t_src.Underlying()
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// Just a change of type, but not value or representation?
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if isValuePreserving(ut_src, ut_dst) {
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c := &ChangeType{X: val}
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c.setType(typ)
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return f.emit(c)
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}
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// Conversion to, or construction of a value of, an interface type?
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if _, ok := ut_dst.(*types.Interface); ok {
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// Assignment from one interface type to another?
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if _, ok := ut_src.(*types.Interface); ok {
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c := &ChangeInterface{X: val}
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c.setType(typ)
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return f.emit(c)
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}
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// Untyped nil constant? Return interface-typed nil constant.
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if ut_src == tUntypedNil {
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return nilConst(typ)
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}
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// Convert (non-nil) "untyped" literals to their default type.
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if t, ok := ut_src.(*types.Basic); ok && t.Info()&types.IsUntyped != 0 {
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val = emitConv(f, val, DefaultType(ut_src))
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}
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f.Pkg.Prog.needMethodsOf(val.Type())
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mi := &MakeInterface{X: val}
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mi.setType(typ)
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return f.emit(mi)
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}
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// Conversion of a compile-time constant value?
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if c, ok := val.(*Const); ok {
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if _, ok := ut_dst.(*types.Basic); ok || c.IsNil() {
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// Conversion of a compile-time constant to
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// another constant type results in a new
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// constant of the destination type and
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// (initially) the same abstract value.
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// We don't truncate the value yet.
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return NewConst(c.Value, typ)
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}
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// We're converting from constant to non-constant type,
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// e.g. string -> []byte/[]rune.
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}
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// A representation-changing conversion?
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// At least one of {ut_src,ut_dst} must be *Basic.
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// (The other may be []byte or []rune.)
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_, ok1 := ut_src.(*types.Basic)
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_, ok2 := ut_dst.(*types.Basic)
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if ok1 || ok2 {
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c := &Convert{X: val}
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c.setType(typ)
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return f.emit(c)
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}
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panic(fmt.Sprintf("in %s: cannot convert %s (%s) to %s", f, val, val.Type(), typ))
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}
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// emitStore emits to f an instruction to store value val at location
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// addr, applying implicit conversions as required by assignability rules.
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//
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func emitStore(f *Function, addr, val Value, pos token.Pos) *Store {
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s := &Store{
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Addr: addr,
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Val: emitConv(f, val, deref(addr.Type())),
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pos: pos,
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}
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f.emit(s)
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return s
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}
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// emitJump emits to f a jump to target, and updates the control-flow graph.
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// Postcondition: f.currentBlock is nil.
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//
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func emitJump(f *Function, target *BasicBlock) {
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b := f.currentBlock
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b.emit(new(Jump))
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addEdge(b, target)
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f.currentBlock = nil
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}
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func (b *BasicBlock) emitJump(target *BasicBlock) {
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b.emit(new(Jump))
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addEdge(b, target)
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}
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// emitIf emits to f a conditional jump to tblock or fblock based on
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// cond, and updates the control-flow graph.
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// Postcondition: f.currentBlock is nil.
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//
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func emitIf(f *Function, cond Value, tblock, fblock *BasicBlock) {
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b := f.currentBlock
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b.emit(&If{Cond: cond})
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addEdge(b, tblock)
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addEdge(b, fblock)
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f.currentBlock = nil
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}
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// emitExtract emits to f an instruction to extract the index'th
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// component of tuple. It returns the extracted value.
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//
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func emitExtract(f *Function, tuple Value, index int) Value {
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e := &Extract{Tuple: tuple, Index: index}
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e.setType(tuple.Type().(*types.Tuple).At(index).Type())
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return f.emit(e)
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}
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// emitTypeAssert emits to f a type assertion value := x.(t) and
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// returns the value. x.Type() must be an interface.
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//
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func emitTypeAssert(f *Function, x Value, t types.Type, pos token.Pos) Value {
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a := &TypeAssert{X: x, AssertedType: t}
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a.setPos(pos)
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a.setType(t)
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return f.emit(a)
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}
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// emitTypeTest emits to f a type test value,ok := x.(t) and returns
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// a (value, ok) tuple. x.Type() must be an interface.
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//
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func emitTypeTest(f *Function, x Value, t types.Type, pos token.Pos) Value {
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a := &TypeAssert{
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X: x,
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AssertedType: t,
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CommaOk: true,
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}
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a.setPos(pos)
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a.setType(types.NewTuple(
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newVar("value", t),
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varOk,
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))
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return f.emit(a)
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}
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// emitTailCall emits to f a function call in tail position. The
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// caller is responsible for all fields of 'call' except its type.
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// Intended for wrapper methods.
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// Precondition: f does/will not use deferred procedure calls.
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// Postcondition: f.currentBlock is nil.
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//
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func emitTailCall(f *Function, call *Call) {
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tresults := f.Signature.Results()
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nr := tresults.Len()
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if nr == 1 {
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call.typ = tresults.At(0).Type()
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} else {
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call.typ = tresults
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}
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tuple := f.emit(call)
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var ret Return
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switch nr {
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case 0:
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// no-op
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case 1:
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ret.Results = []Value{tuple}
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default:
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for i := 0; i < nr; i++ {
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v := emitExtract(f, tuple, i)
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// TODO(adonovan): in principle, this is required:
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// v = emitConv(f, o.Type, f.Signature.Results[i].Type)
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// but in practice emitTailCall is only used when
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// the types exactly match.
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ret.Results = append(ret.Results, v)
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}
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}
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f.emit(&ret)
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f.currentBlock = nil
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}
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// emitImplicitSelections emits to f code to apply the sequence of
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// implicit field selections specified by indices to base value v, and
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// returns the selected value.
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//
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// If v is the address of a struct, the result will be the address of
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// a field; if it is the value of a struct, the result will be the
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// value of a field.
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//
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func emitImplicitSelections(f *Function, v Value, indices []int) Value {
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for _, index := range indices {
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fld := deref(v.Type()).Underlying().(*types.Struct).Field(index)
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if isPointer(v.Type()) {
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instr := &FieldAddr{
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X: v,
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Field: index,
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}
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instr.setType(types.NewPointer(fld.Type()))
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v = f.emit(instr)
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// Load the field's value iff indirectly embedded.
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if isPointer(fld.Type()) {
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v = emitLoad(f, v)
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}
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} else {
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instr := &Field{
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X: v,
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Field: index,
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}
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instr.setType(fld.Type())
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v = f.emit(instr)
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}
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}
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return v
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}
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// emitFieldSelection emits to f code to select the index'th field of v.
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//
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// If wantAddr, the input must be a pointer-to-struct and the result
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// will be the field's address; otherwise the result will be the
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// field's value.
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// Ident id is used for position and debug info.
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//
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func emitFieldSelection(f *Function, v Value, index int, wantAddr bool, id *ast.Ident) Value {
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fld := deref(v.Type()).Underlying().(*types.Struct).Field(index)
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if isPointer(v.Type()) {
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instr := &FieldAddr{
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X: v,
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Field: index,
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}
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instr.setPos(id.Pos())
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instr.setType(types.NewPointer(fld.Type()))
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v = f.emit(instr)
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// Load the field's value iff we don't want its address.
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if !wantAddr {
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v = emitLoad(f, v)
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}
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} else {
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instr := &Field{
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X: v,
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Field: index,
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}
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instr.setPos(id.Pos())
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instr.setType(fld.Type())
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v = f.emit(instr)
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}
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emitDebugRef(f, id, v, wantAddr)
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return v
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}
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// zeroValue emits to f code to produce a zero value of type t,
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// and returns it.
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//
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func zeroValue(f *Function, t types.Type) Value {
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switch t.Underlying().(type) {
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case *types.Struct, *types.Array:
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return emitLoad(f, f.addLocal(t, token.NoPos))
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default:
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return zeroConst(t)
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}
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}
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// createRecoverBlock emits to f a block of code to return after a
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// recovered panic, and sets f.Recover to it.
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//
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// If f's result parameters are named, the code loads and returns
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// their current values, otherwise it returns the zero values of their
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// type.
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//
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// Idempotent.
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//
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func createRecoverBlock(f *Function) {
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if f.Recover != nil {
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return // already created
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}
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saved := f.currentBlock
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f.Recover = f.newBasicBlock("recover")
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f.currentBlock = f.Recover
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var results []Value
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if f.namedResults != nil {
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// Reload NRPs to form value tuple.
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for _, r := range f.namedResults {
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results = append(results, emitLoad(f, r))
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}
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} else {
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R := f.Signature.Results()
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for i, n := 0, R.Len(); i < n; i++ {
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T := R.At(i).Type()
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// Return zero value of each result type.
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results = append(results, zeroValue(f, T))
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}
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}
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f.emit(&Return{Results: results})
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f.currentBlock = saved
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}
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