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// Copyright 2013 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 ir
// Helpers for emitting IR instructions.
import (
"fmt"
"go/ast"
"go/constant"
"go/token"
"go/types"
"golang.org/x/exp/typeparams"
)
// emitAlloc emits to f a new Alloc instruction allocating a variable
// of type typ.
//
// The caller must set Alloc.Heap=true (for a heap-allocated variable)
// or add the Alloc to f.Locals (for a frame-allocated variable).
//
// During building, a variable in f.Locals may have its Heap flag
// set when it is discovered that its address is taken.
// These Allocs are removed from f.Locals at the end.
//
// The builder should generally call one of the emit{New,Local,LocalVar} wrappers instead.
func emitAlloc(f *Function, typ types.Type, source ast.Node, comment string) *Alloc {
v := &Alloc{}
v.comment = comment
v.setType(types.NewPointer(typ))
f.emit(v, source)
return v
}
// emitNew emits to f a new Alloc instruction heap-allocating a
// variable of type typ.
func emitNew(f *Function, typ types.Type, source ast.Node, comment string) *Alloc {
alloc := emitAlloc(f, typ, source, comment)
alloc.Heap = true
return alloc
}
// emitLocal creates a local var for (t, source, comment) and
// emits an Alloc instruction for it.
//
// (Use this function or emitNew for synthetic variables;
// for source-level variables in the same function, use emitLocalVar.)
func emitLocal(f *Function, t types.Type, source ast.Node, comment string) *Alloc {
local := emitAlloc(f, t, source, comment)
f.Locals = append(f.Locals, local)
return local
}
// emitLocalVar creates a local var for v and emits an Alloc instruction for it.
// Subsequent calls to f.lookup(v) return it.
// It applies the appropriate generic instantiation to the type.
func emitLocalVar(f *Function, v *types.Var, source ast.Node) *Alloc {
alloc := emitLocal(f, f.typ(v.Type()), source, v.Name())
f.vars[v] = alloc
return alloc
}
// emitLoad emits to f an instruction to load the address addr into a
// new temporary, and returns the value so defined.
func emitLoad(f *Function, addr Value, source ast.Node) *Load {
v := &Load{X: addr}
v.setType(deref(addr.Type()))
f.emit(v, source)
return v
}
func emitRecv(f *Function, ch Value, commaOk bool, typ types.Type, source ast.Node) Value {
recv := &Recv{
Chan: ch,
CommaOk: commaOk,
}
recv.setType(typ)
return f.emit(recv, source)
}
// emitDebugRef emits to f a DebugRef pseudo-instruction associating
// expression e with value v.
func emitDebugRef(f *Function, e ast.Expr, v Value, isAddr bool) {
ref := makeDebugRef(f, e, v, isAddr)
if ref == nil {
return
}
f.emit(ref, nil)
}
func makeDebugRef(f *Function, e ast.Expr, v Value, isAddr bool) *debugRef {
if !f.debugInfo() {
return nil // debugging not enabled
}
if v == nil || e == nil {
panic("nil")
}
var obj types.Object
e = ast.Unparen(e)
if id, ok := e.(*ast.Ident); ok {
if isBlankIdent(id) {
return nil
}
obj = f.objectOf(id)
switch obj.(type) {
case *types.Nil, *types.Const, *types.Builtin:
return nil
}
}
return &debugRef{
X: v,
Expr: e,
IsAddr: isAddr,
object: obj,
}
}
// emitArith emits to f code to compute the binary operation op(x, y)
// where op is an eager shift, logical or arithmetic operation.
// (Use emitCompare() for comparisons and Builder.logicalBinop() for
// non-eager operations.)
func emitArith(f *Function, op token.Token, x, y Value, t types.Type, source ast.Node) Value {
switch op {
case token.SHL, token.SHR:
x = emitConv(f, x, t, source)
// y may be signed or an 'untyped' constant.
// There is a runtime panic if y is signed and <0. Instead of inserting a check for y<0
// and converting to an unsigned value (like the compiler) leave y as is.
if b, ok := y.Type().Underlying().(*types.Basic); ok && b.Info()&types.IsUntyped != 0 {
// Untyped conversion:
// Spec https://go.dev/ref/spec#Operators:
// The right operand in a shift expression must have integer type or be an untyped constant
// representable by a value of type uint.
y = emitConv(f, y, types.Typ[types.Uint], source)
}
case token.ADD, token.SUB, token.MUL, token.QUO, token.REM, token.AND, token.OR, token.XOR, token.AND_NOT:
x = emitConv(f, x, t, source)
y = emitConv(f, y, t, source)
default:
panic("illegal op in emitArith: " + op.String())
}
v := &BinOp{
Op: op,
X: x,
Y: y,
}
v.setType(t)
return f.emit(v, source)
}
// emitCompare emits to f code compute the boolean result of
// comparison 'x op y'.
func emitCompare(f *Function, op token.Token, x, y Value, source ast.Node) Value {
xt := x.Type().Underlying()
yt := y.Type().Underlying()
// Special case to optimise a tagless SwitchStmt so that
// these are equivalent
// switch { case e: ...}
// switch true { case e: ... }
// if e==true { ... }
// even in the case when e's type is an interface.
// TODO(adonovan): opt: generalise to x==true, false!=y, etc.
if x, ok := x.(*Const); ok && op == token.EQL && x.Value != nil && x.Value.Kind() == constant.Bool && constant.BoolVal(x.Value) {
if yt, ok := yt.(*types.Basic); ok && yt.Info()&types.IsBoolean != 0 {
return y
}
}
if types.Identical(xt, yt) {
// no conversion necessary
} else if _, ok := xt.(*types.Interface); ok && !typeparams.IsTypeParam(x.Type()) {
y = emitConv(f, y, x.Type(), source)
} else if _, ok := yt.(*types.Interface); ok && !typeparams.IsTypeParam(y.Type()) {
x = emitConv(f, x, y.Type(), source)
} else if _, ok := x.(*Const); ok {
x = emitConv(f, x, y.Type(), source)
} else if _, ok := y.(*Const); ok {
y = emitConv(f, y, x.Type(), source)
//lint:ignore SA9003 no-op
} else {
// other cases, e.g. channels. No-op.
}
v := &BinOp{
Op: op,
X: x,
Y: y,
}
v.setType(tBool)
return f.emit(v, source)
}
// isValuePreserving returns true if a conversion from ut_src to
// ut_dst is value-preserving, i.e. just a change of type.
// Precondition: neither argument is a named or alias type.
func isValuePreserving(ut_src, ut_dst types.Type) bool {
// Identical underlying types?
if types.IdenticalIgnoreTags(ut_dst, ut_src) {
return true
}
switch ut_dst.(type) {
case *types.Chan:
// Conversion between channel types?
_, ok := ut_src.(*types.Chan)
return ok
case *types.Pointer:
// Conversion between pointers with identical base types?
_, ok := ut_src.(*types.Pointer)
return ok
}
return false
}
// emitConv emits to f code to convert Value val to exactly type typ,
// and returns the converted value. Implicit conversions are required
// by language assignability rules in assignments, parameter passing,
// etc.
func emitConv(f *Function, val Value, t_dst types.Type, source ast.Node) Value {
t_src := val.Type()
// Identical types? Conversion is a no-op.
if types.Identical(t_src, t_dst) {
return val
}
ut_dst := t_dst.Underlying()
ut_src := t_src.Underlying()
// Conversion to, or construction of a value of, an interface type?
if isNonTypeParamInterface(t_dst) {
// Interface name change?
if isValuePreserving(ut_src, ut_dst) {
c := &ChangeType{X: val}
c.setType(t_dst)
return f.emit(c, source)
}
// Assignment from one interface type to another?
if isNonTypeParamInterface(t_src) {
c := &ChangeInterface{X: val}
c.setType(t_dst)
return f.emit(c, source)
}
// Untyped nil constant? Return interface-typed nil constant.
if ut_src == tUntypedNil {
return zeroConst(t_dst, source)
}
// Convert (non-nil) "untyped" literals to their default type.
if t, ok := ut_src.(*types.Basic); ok && t.Info()&types.IsUntyped != 0 {
val = emitConv(f, val, types.Default(ut_src), source)
}
// Record the types of operands to MakeInterface, if
// non-parameterized, as they are the set of runtime types.
t := val.Type()
if !f.Prog.isParameterized(t) {
addMakeInterfaceType(f.Prog, t)
}
mi := &MakeInterface{X: val}
mi.setType(t_dst)
return f.emit(mi, source)
}
// conversionCase describes an instruction pattern that maybe emitted to
// model d <- s for d in dst_terms and s in src_terms.
// Multiple conversions can match the same pattern.
type conversionCase uint8
const (
changeType conversionCase = 1 << iota
sliceToArray
sliceToArrayPtr
sliceTo0Array
sliceTo0ArrayPtr
convert
)
// classify the conversion case of a source type us to a destination type ud.
// us and ud are underlying types (not *Named or *Alias)
classify := func(s, d types.Type) conversionCase {
// Just a change of type, but not value or representation?
if isValuePreserving(s, d) {
return changeType
}
// Conversion from slice to array or slice to array pointer?
if slice, ok := s.(*types.Slice); ok {
var arr *types.Array
var ptr bool
// Conversion from slice to array pointer?
switch d := d.(type) {
case *types.Array:
arr = d
case *types.Pointer:
arr, _ = d.Elem().Underlying().(*types.Array)
ptr = true
}
if arr != nil && types.Identical(slice.Elem(), arr.Elem()) {
if arr.Len() == 0 {
if ptr {
return sliceTo0ArrayPtr
} else {
return sliceTo0Array
}
}
if ptr {
return sliceToArrayPtr
} else {
return sliceToArray
}
}
}
// The only remaining case in well-typed code is a representation-
// changing conversion of basic types (possibly with []byte/[]rune).
if !isBasic(s) && !isBasic(d) {
panic(fmt.Sprintf("in %s: cannot convert term %s (%s [within %s]) to type %s [within %s]", f, val, val.Type(), s, t_dst, d))
}
return convert
}
var classifications conversionCase
underIs(ut_src, func(us types.Type) bool {
return underIs(ut_dst, func(ud types.Type) bool {
if us != nil && ud != nil {
classifications |= classify(us, ud)
}
return classifications != 0
})
})
if classifications == 0 {
panic(fmt.Sprintf("in %s: cannot convert %s (%s) to %s", f, val, val.Type(), t_dst))
}
// Conversion of a compile-time constant value?
if c, ok := val.(*Const); ok {
// Conversion to a basic type?
if isBasic(ut_dst) {
// Conversion of a compile-time constant to
// another constant type results in a new
// constant of the destination type and
// (initially) the same abstract value.
// We don't truncate the value yet.
return NewConst(c.Value, t_dst, source)
}
// Can we always convert from zero value without panicking?
const mayPanic = sliceToArray | sliceToArrayPtr
if c.Value == nil && classifications&mayPanic == 0 {
return NewConst(nil, t_dst, source)
}
// We're converting from constant to non-constant type,
// e.g. string -> []byte/[]rune.
}
switch classifications {
case changeType: // representation-preserving change
c := &ChangeType{X: val}
c.setType(t_dst)
return f.emit(c, source)
case sliceToArrayPtr, sliceTo0ArrayPtr: // slice to array pointer
c := &SliceToArrayPointer{X: val}
c.setType(t_dst)
return f.emit(c, source)
case sliceToArray: // slice to arrays (not zero-length)
p := &SliceToArray{X: val}
p.setType(t_dst)
return f.emit(p, source)
case sliceTo0Array: // slice to zero-length arrays (constant)
return zeroConst(t_dst, source)
case convert: // representation-changing conversion
c := &Convert{X: val}
c.setType(t_dst)
return f.emit(c, source)
default: // The conversion represents a cross product.
c := &MultiConvert{X: val, from: t_src, to: t_dst}
c.setType(t_dst)
return f.emit(c, source)
}
}
// emitTypeCoercion emits to f code to coerce the type of a
// Value v to exactly type typ, and returns the coerced value.
//
// Requires that coercing v.Typ() to typ is a value preserving change.
//
// Currently used only when v.Type() is a type instance of typ or vice versa.
// A type v is a type instance of a type t if there exists a
// type parameter substitution σ s.t. σ(v) == t. Example:
//
// σ(func(T) T) == func(int) int for σ == [T ↦ int]
//
// This happens in instantiation wrappers for conversion
// from an instantiation to a parameterized type (and vice versa)
// with σ substituting f.typeparams by f.typeargs.
func emitTypeCoercion(f *Function, v Value, typ types.Type, source ast.Node) Value {
if types.Identical(v.Type(), typ) {
return v // no coercion needed
}
// TODO(taking): for instances should we record which side is the instance?
c := &ChangeType{
X: v,
}
c.setType(typ)
f.emit(c, source)
return c
}
// emitStore emits to f an instruction to store value val at location
// addr, applying implicit conversions as required by assignability rules.
func emitStore(f *Function, addr, val Value, source ast.Node) *Store {
typ := deref(addr.Type())
s := &Store{
Addr: addr,
Val: emitConv(f, val, typ, source),
}
f.emit(s, source)
return s
}
// emitJump emits to f a jump to target, and updates the control-flow graph.
// Postcondition: f.currentBlock is nil.
func emitJump(f *Function, target *BasicBlock, source ast.Node) *Jump {
b := f.currentBlock
j := new(Jump)
b.emit(j, source)
addEdge(b, target)
f.currentBlock = nil
return j
}
// emitIf emits to f a conditional jump to tblock or fblock based on
// cond, and updates the control-flow graph.
// Postcondition: f.currentBlock is nil.
func emitIf(f *Function, cond Value, tblock, fblock *BasicBlock, source ast.Node) *If {
b := f.currentBlock
stmt := &If{Cond: cond}
b.emit(stmt, source)
addEdge(b, tblock)
addEdge(b, fblock)
f.currentBlock = nil
return stmt
}
// emitExtract emits to f an instruction to extract the index'th
// component of tuple. It returns the extracted value.
func emitExtract(f *Function, tuple Value, index int, source ast.Node) Value {
e := &Extract{Tuple: tuple, Index: index}
e.setType(tuple.Type().(*types.Tuple).At(index).Type())
return f.emit(e, source)
}
// emitTypeAssert emits to f a type assertion value := x.(t) and
// returns the value. x.Type() must be an interface.
func emitTypeAssert(f *Function, x Value, t types.Type, source ast.Node) Value {
a := &TypeAssert{X: x, AssertedType: t}
a.setType(t)
return f.emit(a, source)
}
// emitTypeTest emits to f a type test value,ok := x.(t) and returns
// a (value, ok) tuple. x.Type() must be an interface.
func emitTypeTest(f *Function, x Value, t types.Type, source ast.Node) Value {
a := &TypeAssert{
X: x,
AssertedType: t,
CommaOk: true,
}
a.setType(types.NewTuple(
newVar("value", t),
varOk,
))
return f.emit(a, source)
}
// emitTailCall emits to f a function call in tail position. The
// caller is responsible for all fields of 'call' except its type.
// Intended for wrapper methods.
// Precondition: f does/will not use deferred procedure calls.
// Postcondition: f.currentBlock is nil.
func emitTailCall(f *Function, call *Call, source ast.Node) {
tresults := f.Signature.Results()
nr := tresults.Len()
if nr == 1 {
call.typ = tresults.At(0).Type()
} else {
call.typ = tresults
}
tuple := emitCall(f, call, source)
var ret Return
switch nr {
case 0:
// no-op
case 1:
ret.Results = []Value{tuple}
default:
for i := range nr {
v := emitExtract(f, tuple, i, source)
// TODO(adonovan): in principle, this is required:
// v = emitConv(f, o.Type, f.Signature.Results[i].Type)
// but in practice emitTailCall is only used when
// the types exactly match.
ret.Results = append(ret.Results, v)
}
}
f.emit(&ret, source)
f.currentBlock = nil
}
// emitCall emits a call instruction. If the callee is "no return",
// it also emits a panic to eliminate infeasible CFG edges.
func emitCall(fn *Function, call *Call, source ast.Node) Value {
res := fn.emit(call, source)
callee := call.Call.StaticCallee()
if callee != nil &&
callee.object != nil &&
fn.Prog.noReturn != nil &&
fn.Prog.noReturn(callee.object) {
// Call doesn't return normally. Either it doesn't return at all
// (infinitely blocked or exitting the process), or it unwinds the stack
// (panic, runtime.Goexit). Model this as a panic.
fn.emit(&Panic{
X: emitConv(fn, vNoReturn, tEface, source),
}, source)
fn.currentBlock = fn.newBasicBlock("unreachable")
}
return res
}
// emitImplicitSelections emits to f code to apply the sequence of
// implicit field selections specified by indices to base value v, and
// returns the selected value.
//
// If v is the address of a struct, the result will be the address of
// a field; if it is the value of
87EE
a struct, the result will be the
// value of a field.
func emitImplicitSelections(f *Function, v Value, indices []int, source ast.Node) Value {
for _, index := range indices {
// We may have a generic type containing a pointer, or a pointer to a generic type containing a struct. A
// pointer to a generic containing a pointer to a struct shouldn't be possible because the outer pointer gets
// dereferenced implicitly before we get here.
if isPointerCore(v.Type()) {
fld := fieldOf(deref(v.Type()), index)
instr := &FieldAddr{
X: v,
Field: index,
}
instr.setType(types.NewPointer(fld.Type()))
v = f.emit(instr, source)
// Load the field's value iff indirectly embedded.
if isPointerCore(fld.Type()) {
v = emitLoad(f, v, source)
}
} else {
fld := fieldOf(v.Type(), index)
instr := &Field{
X: v,
Field: index,
}
instr.setType(fld.Type())
v = f.emit(instr, source)
}
}
return v
}
// emitFieldSelection emits to f code to select the index'th field of v.
//
// If wantAddr, the input must be a pointer-to-struct and the result
// will be the field's address; otherwise the result will be the
// field's value.
// Ident id is used for position and debug info.
func emitFieldSelection(f *Function, v Value, index int, wantAddr bool, id *ast.Ident) Value {
if isPointerCore(v.Type()) {
fld := fieldOf(deref(v.Type()), index)
instr := &FieldAddr{
X: v,
Field: index,
}
instr.setSource(id)
instr.setType(types.NewPointer(fld.Type()))
v = f.emit(instr, id)
// Load the field's value iff we don't want its address.
if !wantAddr {
v = emitLoad(f, v, id)
}
} else {
fld := fieldOf(v.Type(), index)
instr := &Field{
X: v,
Field: index,
}
instr.setSource(id)
instr.setType(fld.Type())
v = f.emit(instr, id)
}
emitDebugRef(f, id, v, wantAddr)
return v
}
// createRecoverBlock emits to f a block of code to return after a
// recovered panic, and sets f.Recover to it.
//
// If f's result parameters are named, the code loads and returns
// their current values, otherwise it returns the zero values of their
// type.
//
// Idempotent.
func createRecoverBlock(f *Function) {
if f.Recover != nil {
return // already created
}
saved := f.currentBlock
f.Recover = f.newBasicBlock("recover")
f.currentBlock = f.Recover
var results []Value
// Reload NRPs to form value tuple.
for _, nr := range f.results {
results = append(results, emitLoad(f, nr, nr.source))
}
f.emit(&Return{Results: results}, nil)
f.currentBlock = saved
}