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package x86
import (
"errors"
"github.com/mmcloughlin/avo/ir"
"github.com/mmcloughlin/avo/operand"
)
// build constructs an instruction object from a list of acceptable forms, and
// given input operands and suffixes.
func build(forms []form, suffixes sffxs, ops []operand.Op) (*ir.Instruction, error) {
for i := range forms {
f := &forms[i]
if f.match(suffixes, ops) {
return f.build(suffixes, ops), nil
}
}
return nil, errors.New("bad operands")
}
// form represents an instruction form.
type form struct {
Opcode opc
SuffixesClass sffxscls
Features feature
ISAs isas
Arity uint8
Operands oprnds
}
// feature is a flags enumeration type representing instruction properties.
type feature uint8
const (
featureTerminal feature = 1 << iota
featureBranch
featureConditionalBranch
featureCancellingInputs
)
// oprnds is a list of explicit and implicit operands of an instruction form.
// The size of the array is output by optab generator.
type oprnds [maxoperands]oprnd
// oprnd represents an explicit or implicit operand to an instruction form.
type oprnd struct {
Type uint8
Implicit bool
Action action
}
// action an instruction form applies to an operand.
type action uint8
const (
actionN action = iota
actionR
actionW
actionRW action = actionR | actionW
)
// Read reports if the action includes read.
func (a action) Read() bool { return (a & actionR) != 0 }
// Read reports if the action includes write.
func (a action) Write() bool { return (a & actionW) != 0 }
// match reports whether this form matches the given suffixes and operand
// list.
func (f *form) match(suffixes sffxs, ops []operand.Op) bool {
// Match suffix.
accept := f.SuffixesClass.SuffixesSet()
if !accept[suffixes] {
return false
}
// Match operands.
if len(ops) != int(f.Arity) {
return false
}
for i, op := range ops {
t := oprndtype(f.Operands[i].Type)
if !t.Match(op) {
return false
}
}
return true
}
// build the full instruction object for this form and the given suffixes and
// operands. Assumes the form already matches the inputs.
func (f *form) build(suffixes sffxs, ops []operand.Op) *ir.Instruction {
// Base instruction properties.
i := &ir.Instruction{
Opcode: f.Opcode.String(),
Suffixes: suffixes.Strings(),
Operands: ops,
IsTerminal: (f.Features & featureTerminal) != 0,
IsBranch: (f.Features & featureBranch) != 0,
IsConditional: (f.Features & featureConditionalBranch) != 0,
CancellingInputs: (f.Features & featureCancellingInputs) != 0,
ISA: f.ISAs.List(),
}
// Input/output operands.
for _, spec := range f.Operands {
if spec.Type == 0 {
break
}
var op operand.Op
if spec.Implicit {
op = implreg(spec.Type).Register()
} else {
op, ops = ops[0], ops[1:]
}
if spec.Action.Read() {
i.Inputs = append(i.Inputs, op)
}
if spec.Action.Write() {
i.Outputs = append(i.Outputs, op)
}
}
return i
}
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