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interpreter.go
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interpreter.go
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package ir
// This file provides functionality to interpret very basic Go SSA, for
// compile-time initialization of globals.
import (
"errors"
"fmt"
"go/constant"
"go/token"
"go/types"
"strings"
"golang.org/x/tools/go/ssa"
)
var ErrCGoWrapper = errors.New("tinygo internal: cgo wrapper") // a signal, not an error
// Ignore these calls (replace with a zero return value) when encountered during
// interpretation.
var ignoreInitCalls = map[string]struct{}{
"syscall.runtime_envs": struct{}{},
"syscall/js.predefValue": struct{}{},
"(syscall/js.Value).Get": struct{}{},
"(syscall/js.Value).New": struct{}{},
"(syscall/js.Value).Int": struct{}{},
"os.init$1": struct{}{},
}
// Interpret instructions as far as possible, and drop those instructions from
// the basic block.
func (p *Program) Interpret(block *ssa.BasicBlock, dumpSSA bool) error {
if dumpSSA {
fmt.Printf("\ninterpret: %s\n", block.Parent().Pkg.Pkg.Path())
}
for {
i, err := p.interpret(block.Instrs, nil, nil, nil, dumpSSA)
if err == ErrCGoWrapper {
// skip this instruction
block.Instrs = block.Instrs[i+1:]
continue
}
block.Instrs = block.Instrs[i:]
return err
}
}
// Interpret instructions as far as possible, and return the index of the first
// unknown instruction.
func (p *Program) interpret(instrs []ssa.Instruction, paramKeys []*ssa.Parameter, paramValues []Value, results []Value, dumpSSA bool) (int, error) {
locals := map[ssa.Value]Value{}
for i, key := range paramKeys {
locals[key] = paramValues[i]
}
for i, instr := range instrs {
if _, ok := instr.(*ssa.DebugRef); ok {
continue
}
if dumpSSA {
if val, ok := instr.(ssa.Value); ok && val.Name() != "" {
fmt.Printf("\t%s: %s = %s\n", instr.Parent().RelString(nil), val.Name(), val.String())
} else {
fmt.Printf("\t%s: %s\n", instr.Parent().RelString(nil), instr.String())
}
}
switch instr := instr.(type) {
case *ssa.Alloc:
alloc, err := p.getZeroValue(instr.Type().Underlying().(*types.Pointer).Elem())
if err != nil {
return i, err
}
locals[instr] = &PointerValue{nil, &alloc}
case *ssa.BinOp:
if typ, ok := instr.Type().(*types.Basic); ok && typ.Kind() == types.String {
// Concatenate two strings.
// This happens in the time package, for example.
x, err := p.getValue(instr.X, locals)
if err != nil {
return i, err
}
y, err := p.getValue(instr.Y, locals)
if err != nil {
return i, err
}
xstr := constant.StringVal(x.(*ConstValue).Expr.Value)
ystr := constant.StringVal(y.(*ConstValue).Expr.Value)
locals[instr] = &ConstValue{ssa.NewConst(constant.MakeString(xstr+ystr), types.Typ[types.String])}
} else {
return i, errors.New("init: unknown binop: " + instr.String())
}
case *ssa.Call:
common := instr.Common()
callee := common.StaticCallee()
if callee == nil {
return i, nil // don't understand dynamic dispatch
}
if _, ok := ignoreInitCalls[callee.String()]; ok {
// These calls are not needed and can be ignored, for the time
// being.
results := make([]Value, callee.Signature.Results().Len())
for i := range results {
var err error
results[i], err = p.getZeroValue(callee.Signature.Results().At(i).Type())
if err != nil {
return i, err
}
}
if len(results) == 1 {
locals[instr] = results[0]
} else if len(results) > 1 {
locals[instr] = &StructValue{Fields: results}
}
continue
}
if callee.String() == "os.NewFile" {
// Emulate the creation of os.Stdin, os.Stdout and os.Stderr.
resultPtrType := callee.Signature.Results().At(0).Type().(*types.Pointer)
resultStructOuterType := resultPtrType.Elem().Underlying().(*types.Struct)
if resultStructOuterType.NumFields() != 1 {
panic("expected 1 field in os.File struct")
}
fileInnerPtrType := resultStructOuterType.Field(0).Type().(*types.Pointer)
fileInnerType := fileInnerPtrType.Elem().(*types.Named)
fileInnerStructType := fileInnerType.Underlying().(*types.Struct)
fileInner, err := p.getZeroValue(fileInnerType) // os.file
if err != nil {
return i, err
}
for fieldIndex := 0; fieldIndex < fileInnerStructType.NumFields(); fieldIndex++ {
field := fileInnerStructType.Field(fieldIndex)
if field.Name() == "name" {
// Set the 'name' field.
name, err := p.getValue(common.Args[1], locals)
if err != nil {
return i, err
}
fileInner.(*StructValue).Fields[fieldIndex] = name
} else if field.Type().String() == "internal/poll.FD" {
// Set the file descriptor field.
field := field.Type().Underlying().(*types.Struct)
for subfieldIndex := 0; subfieldIndex < field.NumFields(); subfieldIndex++ {
subfield := field.Field(subfieldIndex)
if subfield.Name() == "Sysfd" {
sysfd, err := p.getValue(common.Args[0], locals)
if err != nil {
return i, err
}
sysfd = &ConstValue{Expr: ssa.NewConst(sysfd.(*ConstValue).Expr.Value, subfield.Type())}
fileInner.(*StructValue).Fields[fieldIndex].(*StructValue).Fields[subfieldIndex] = sysfd
}
}
}
}
fileInnerPtr := &PointerValue{fileInnerPtrType, &fileInner} // *os.file
var fileOuter Value = &StructValue{Type: resultPtrType.Elem(), Fields: []Value{fileInnerPtr}} // os.File
result := &PointerValue{resultPtrType.Elem(), &fileOuter} // *os.File
locals[instr] = result
continue
}
if canInterpret(callee) {
params := make([]Value, len(common.Args))
for i, arg := range common.Args {
val, err := p.getValue(arg, locals)
if err != nil {
return i, err
}
params[i] = val
}
results := make([]Value, callee.Signature.Results().Len())
subi, err := p.interpret(callee.Blocks[0].Instrs, callee.Params, params, results, dumpSSA)
if err != nil {
return i, err
}
if subi != len(callee.Blocks[0].Instrs) {
return i, errors.New("init: could not interpret all instructions of subroutine")
}
if len(results) == 1 {
locals[instr] = results[0]
} else {
panic("unimplemented: not exactly 1 result")
}
continue
}
if callee.Object() == nil || callee.Object().Name() == "init" {
return i, nil // arrived at the init#num functions
}
return i, errors.New("todo: init call: " + callee.String())
case *ssa.ChangeType:
x, err := p.getValue(instr.X, locals)
if err != nil {
return i, err
}
// The only case when we need to bitcast is when casting between named
// struct types, as those are actually different in LLVM. Let's just
// bitcast all struct types for ease of use.
if _, ok := instr.Type().Underlying().(*types.Struct); ok {
return i, errors.New("todo: init: " + instr.String())
}
locals[instr] = x
case *ssa.Convert:
x, err := p.getValue(instr.X, locals)
if err != nil {
return i, err
}
typeFrom := instr.X.Type().Underlying()
switch typeTo := instr.Type().Underlying().(type) {
case *types.Basic:
if typeTo.Kind() == types.String {
return i, nil
}
if _, ok := typeFrom.(*types.Pointer); ok && typeTo.Kind() == types.UnsafePointer {
locals[instr] = &PointerBitCastValue{typeTo, x}
} else if typeFrom, ok := typeFrom.(*types.Basic); ok {
if typeFrom.Kind() == types.UnsafePointer && typeTo.Kind() == types.Uintptr {
locals[instr] = &PointerToUintptrValue{x}
} else if typeFrom.Info()&types.IsInteger != 0 && typeTo.Info()&types.IsInteger != 0 {
locals[instr] = &ConstValue{Expr: ssa.NewConst(x.(*ConstValue).Expr.Value, typeTo)}
} else {
return i, nil
}
} else {
return i, nil
}
case *types.Pointer:
if typeFrom, ok := typeFrom.(*types.Basic); ok && typeFrom.Kind() == types.UnsafePointer {
locals[instr] = &PointerBitCastValue{typeTo, x}
} else {
panic("expected unsafe pointer conversion")
}
default:
return i, nil
}
case *ssa.DebugRef:
// ignore
case *ssa.Extract:
tuple, err := p.getValue(instr.Tuple, locals)
if err != nil {
return i, err
}
locals[instr] = tuple.(*StructValue).Fields[instr.Index]
case *ssa.FieldAddr:
x, err := p.getValue(instr.X, locals)
if err != nil {
return i, err
}
var structVal *StructValue
switch x := x.(type) {
case *GlobalValue:
structVal = x.Global.initializer.(*StructValue)
case *PointerValue:
structVal = (*x.Elem).(*StructValue)
default:
panic("expected a pointer")
}
locals[instr] = &PointerValue{nil, &structVal.Fields[instr.Field]}
case *ssa.IndexAddr:
x, err := p.getValue(instr.X, locals)
if err != nil {
return i, err
}
if cnst, ok := instr.Index.(*ssa.Const); ok {
index, _ := constant.Int64Val(cnst.Value)
switch xPtr := x.(type) {
case *GlobalValue:
x = xPtr.Global.initializer
case *PointerValue:
x = *xPtr.Elem
default:
panic("expected a pointer")
}
switch x := x.(type) {
case *ArrayValue:
locals[instr] = &PointerValue{nil, &x.Elems[index]}
default:
return i, errors.New("todo: init IndexAddr not on an array or struct")
}
} else {
return i, errors.New("todo: init IndexAddr index: " + instr.Index.String())
}
case *ssa.MakeMap:
locals[instr] = &MapValue{instr.Type().Underlying().(*types.Map), nil, nil}
case *ssa.MapUpdate:
// Assume no duplicate keys exist. This is most likely true for
// autogenerated code, but may not be true when trying to interpret
// user code.
key, err := p.getValue(instr.Key, locals)
if err != nil {
return i, err
}
value, err := p.getValue(instr.Value, locals)
if err != nil {
return i, err
}
x := locals[instr.Map].(*MapValue)
x.Keys = append(x.Keys, key)
x.Values = append(x.Values, value)
case *ssa.Return:
for i, r := range instr.Results {
val, err := p.getValue(r, locals)
if err != nil {
return i, err
}
results[i] = val
}
case *ssa.Slice:
// Turn a just-allocated array into a slice.
if instr.Low != nil || instr.High != nil || instr.Max != nil {
return i, errors.New("init: slice expression with bounds")
}
source, err := p.getValue(instr.X, locals)
if err != nil {
return i, err
}
switch source := source.(type) {
case *PointerValue: // pointer to array
array := (*source.Elem).(*ArrayValue)
locals[instr] = &SliceValue{instr.Type().Underlying().(*types.Slice), array}
default:
return i, errors.New("init: unknown slice type")
}
case *ssa.Store:
if addr, ok := instr.Addr.(*ssa.Global); ok {
if strings.HasPrefix(instr.Addr.Name(), "__cgofn__cgo_") || strings.HasPrefix(instr.Addr.Name(), "_cgo_") {
// Ignore CGo global variables which we don't use.
continue
}
value, err := p.getValue(instr.Val, locals)
if err != nil {
return i, err
}
p.GetGlobal(addr).initializer = value
} else if addr, ok := locals[instr.Addr]; ok {
value, err := p.getValue(instr.Val, locals)
if err != nil {
return i, err
}
if addr, ok := addr.(*PointerValue); ok {
*(addr.Elem) = value
} else {
panic("store to non-pointer")
}
} else {
return i, errors.New("todo: init Store: " + instr.String())
}
case *ssa.UnOp:
if instr.Op != token.MUL || instr.CommaOk {
return i, errors.New("init: unknown unop: " + instr.String())
}
valPtr, err := p.getValue(instr.X, locals)
if err != nil {
return i, err
}
switch valPtr := valPtr.(type) {
case *GlobalValue:
locals[instr] = valPtr.Global.initializer
case *PointerValue:
locals[instr] = *valPtr.Elem
default:
panic("expected a pointer")
}
default:
return i, nil
}
}
return len(instrs), nil
}
// Check whether this function can be interpreted at compile time. For that, it
// needs to only contain relatively simple instructions (for example, no control
// flow).
func canInterpret(callee *ssa.Function) bool {
if len(callee.Blocks) != 1 || callee.Signature.Results().Len() != 1 {
// No control flow supported so only one basic block.
// Only exactly one return value supported right now so check that as
// well.
return false
}
for _, instr := range callee.Blocks[0].Instrs {
switch instr.(type) {
// Ignore all functions fully supported by Program.interpret()
// above.
case *ssa.Alloc:
case *ssa.ChangeType:
case *ssa.DebugRef:
case *ssa.Extract:
case *ssa.FieldAddr:
case *ssa.IndexAddr:
case *ssa.MakeMap:
case *ssa.MapUpdate:
case *ssa.Return:
case *ssa.Slice:
case *ssa.Store:
case *ssa.UnOp:
default:
return false
}
}
return true
}
func (p *Program) getValue(value ssa.Value, locals map[ssa.Value]Value) (Value, error) {
switch value := value.(type) {
case *ssa.Const:
return &ConstValue{value}, nil
case *ssa.Function:
return &FunctionValue{value.Type(), value}, nil
case *ssa.Global:
if strings.HasPrefix(value.Name(), "__cgofn__cgo_") || strings.HasPrefix(value.Name(), "_cgo_") {
// Ignore CGo global variables which we don't use.
return nil, ErrCGoWrapper
}
g := p.GetGlobal(value)
if g.initializer == nil {
value, err := p.getZeroValue(value.Type().Underlying().(*types.Pointer).Elem())
if err != nil {
return nil, err
}
g.initializer = value
}
return &GlobalValue{g}, nil
default:
if local, ok := locals[value]; ok {
return local, nil
} else {
return nil, errors.New("todo: init: unknown value: " + value.String())
}
}
}
func (p *Program) getZeroValue(t types.Type) (Value, error) {
switch typ := t.Underlying().(type) {
case *types.Array:
elems := make([]Value, typ.Len())
for i := range elems {
elem, err := p.getZeroValue(typ.Elem())
if err != nil {
return nil, err
}
elems[i] = elem
}
return &ArrayValue{typ.Elem(), elems}, nil
case *types.Basic:
return &ZeroBasicValue{typ}, nil
case *types.Signature:
return &FunctionValue{typ, nil}, nil
case *types.Map:
return &MapValue{typ, nil, nil}, nil
case *types.Pointer:
return &PointerValue{typ, nil}, nil
case *types.Struct:
elems := make([]Value, typ.NumFields())
for i := range elems {
elem, err := p.getZeroValue(typ.Field(i).Type())
if err != nil {
return nil, err
}
elems[i] = elem
}
return &StructValue{t, elems}, nil
case *types.Slice:
return &SliceValue{typ, nil}, nil
default:
return nil, errors.New("todo: init: unknown global type: " + typ.String())
}
}
// Boxed value for interpreter.
type Value interface {
}
type ConstValue struct {
Expr *ssa.Const
}
type ZeroBasicValue struct {
Type *types.Basic
}
type PointerValue struct {
Type types.Type
Elem *Value
}
type FunctionValue struct {
Type types.Type
Elem *ssa.Function
}
type PointerBitCastValue struct {
Type types.Type
Elem Value
}
type PointerToUintptrValue struct {
Elem Value
}
type GlobalValue struct {
Global *Global
}
type ArrayValue struct {
ElemType types.Type
Elems []Value
}
type StructValue struct {
Type types.Type // types.Struct or types.Named
Fields []Value
}
type SliceValue struct {
Type *types.Slice
Array *ArrayValue
}
type MapValue struct {
Type *types.Map
Keys []Value
Values []Value
}