forked from TrueCloudLab/neoneo-go
compiler: emit short jumps where possible
Convert long jumps to short ones if the offset can be represented in a single byte. Close #805.
This commit is contained in:
Evgenii Stratonikov
parent
681e81420a
commit
cfa62e7051
2 changed files with 246 additions and 8 deletions
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@ -1613,8 +1613,8 @@ func CodeGen(info *buildInfo) ([]byte, *DebugInfo, error) {
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return nil, nil, err
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}
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buf := c.prog.Bytes()
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if err := c.writeJumps(buf); err != nil {
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buf, err := c.writeJumps(c.prog.Bytes())
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if err != nil {
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return nil, nil, err
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}
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return buf, c.emitDebugInfo(buf), nil
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@ -1629,15 +1629,14 @@ func (c *codegen) resolveFuncDecls(f *ast.File, pkg *types.Package) {
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}
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}
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func (c *codegen) writeJumps(b []byte) error {
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func (c *codegen) writeJumps(b []byte) ([]byte, error) {
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ctx := vm.NewContext(b)
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var offsets []int
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for op, _, err := ctx.Next(); err == nil && ctx.NextIP() < len(b); op, _, err = ctx.Next() {
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switch op {
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case opcode.JMP, opcode.JMPIFNOT, opcode.JMPIF, opcode.CALL,
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opcode.JMPEQ, opcode.JMPNE,
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opcode.JMPGT, opcode.JMPGE, opcode.JMPLE, opcode.JMPLT:
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// Noop, assumed to be correct already. If you're fixing #905,
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// make sure not to break "len" and "append" handling above.
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case opcode.JMPL, opcode.JMPIFL, opcode.JMPIFNOTL,
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opcode.JMPEQL, opcode.JMPNEL,
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opcode.JMPGTL, opcode.JMPGEL, opcode.JMPLEL, opcode.JMPLTL,
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@ -1648,15 +1647,135 @@ func (c *codegen) writeJumps(b []byte) error {
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index := binary.LittleEndian.Uint16(arg)
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if int(index) > len(c.l) {
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return fmt.Errorf("unexpected label number: %d (max %d)", index, len(c.l))
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return nil, fmt.Errorf("unexpected label number: %d (max %d)", index, len(c.l))
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}
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offset := c.l[index] - nextIP + 5
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if offset > math.MaxInt32 || offset < math.MinInt32 {
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return fmt.Errorf("label offset is too big at the instruction %d: %d (max %d, min %d)",
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return nil, fmt.Errorf("label offset is too big at the instruction %d: %d (max %d, min %d)",
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nextIP-5, offset, math.MaxInt32, math.MinInt32)
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}
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if op != opcode.PUSHA && math.MinInt8 <= offset && offset <= math.MaxInt8 {
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offsets = append(offsets, ctx.IP())
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}
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binary.LittleEndian.PutUint32(arg, uint32(offset))
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}
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}
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return nil
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// Correct function ip range.
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// Note: indices are sorted in increasing order.
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for _, f := range c.funcs {
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loop:
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for _, ind := range offsets {
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switch {
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case ind > int(f.rng.End):
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break loop
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case ind < int(f.rng.Start):
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f.rng.Start -= longToShortRemoveCount
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f.rng.End -= longToShortRemoveCount
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case ind >= int(f.rng.Start):
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f.rng.End -= longToShortRemoveCount
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}
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}
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}
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return shortenJumps(b, offsets), nil
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}
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// longToShortRemoveCount is a difference between short and long instruction sizes in bytes.
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const longToShortRemoveCount = 3
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// shortenJumps returns converts b to a program where all long JMP*/CALL* specified by absolute offsets,
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// are replaced with their corresponding short counterparts. It panics if either b or offsets are invalid.
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// This is done in 2 passes:
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// 1. Alter jump offsets taking into account parts to be removed.
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// 2. Perform actual removal of jump targets.
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// Note: after jump offsets altering, there can appear new candidates for conversion.
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// These are ignored for now.
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func shortenJumps(b []byte, offsets []int) []byte {
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if len(offsets) == 0 {
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return b
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}
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// 1. Alter existing jump offsets.
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ctx := vm.NewContext(b)
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for op, _, err := ctx.Next(); err == nil && ctx.IP() < len(b); op, _, err = ctx.Next() {
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// we can't use arg returned by ctx.Next() because it is copied
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nextIP := ctx.NextIP()
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ip := ctx.IP()
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switch op {
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case opcode.JMP, opcode.JMPIFNOT, opcode.JMPIF, opcode.CALL,
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opcode.JMPEQ, opcode.JMPNE,
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opcode.JMPGT, opcode.JMPGE, opcode.JMPLE, opcode.JMPLT:
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offset := int(int8(b[nextIP-1]))
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offset += calcOffsetCorrection(ip, ip+offset, offsets)
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b[nextIP-1] = byte(offset)
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case opcode.JMPL, opcode.JMPIFL, opcode.JMPIFNOTL,
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opcode.JMPEQL, opcode.JMPNEL,
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opcode.JMPGTL, opcode.JMPGEL, opcode.JMPLEL, opcode.JMPLTL,
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opcode.CALLL, opcode.PUSHA:
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arg := b[nextIP-4:]
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offset := int(int32(binary.LittleEndian.Uint32(arg)))
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offset += calcOffsetCorrection(ip, ip+offset, offsets)
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binary.LittleEndian.PutUint32(arg, uint32(offset))
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}
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}
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// 2. Convert instructions.
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copyOffset := 0
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l := len(offsets)
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b[offsets[0]] = toShortForm(b[offsets[0]])
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for i := 0; i < l; i++ {
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start := offsets[i] + 2
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end := len(b)
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if i != l-1 {
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end = offsets[i+1] + 2
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b[offsets[i+1]] = toShortForm(b[offsets[i+1]])
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}
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copy(b[start-copyOffset:], b[start+3:end])
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copyOffset += longToShortRemoveCount
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}
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return b[:len(b)-copyOffset]
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}
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func calcOffsetCorrection(ip, target int, offsets []int) int {
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cnt := 0
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start := sort.Search(len(offsets), func(i int) bool {
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return offsets[i] >= ip || offsets[i] >= target
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})
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for i := start; i < len(offsets) && (offsets[i] < target || offsets[i] <= ip); i++ {
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ind := offsets[i]
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if ip <= ind && ind < target ||
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ind != ip && target <= ind && ind <= ip {
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cnt += longToShortRemoveCount
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}
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}
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if ip < target {
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return -cnt
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}
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return cnt
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}
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func toShortForm(b byte) byte {
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switch op := opcode.Opcode(b); op {
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case opcode.JMPL:
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return byte(opcode.JMP)
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case opcode.JMPIFL:
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return byte(opcode.JMPIF)
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case opcode.JMPIFNOTL:
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return byte(opcode.JMPIFNOT)
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case opcode.JMPEQL:
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return byte(opcode.JMPEQ)
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case opcode.JMPNEL:
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return byte(opcode.JMPNE)
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case opcode.JMPGTL:
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return byte(opcode.JMPGT)
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case opcode.JMPGEL:
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return byte(opcode.JMPGE)
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case opcode.JMPLEL:
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return byte(opcode.JMPLE)
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case opcode.JMPLTL:
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return byte(opcode.JMPLT)
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case opcode.CALLL:
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return byte(opcode.CALL)
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default:
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panic(fmt.Errorf("invalid opcode: %s", op))
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}
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}
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119
pkg/compiler/jumps_test.go
Normal file
119
pkg/compiler/jumps_test.go
Normal file
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@ -0,0 +1,119 @@
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package compiler
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import (
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"testing"
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"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
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"github.com/stretchr/testify/require"
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)
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func testShortenJumps(t *testing.T, before, after []opcode.Opcode, indices []int) {
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prog := make([]byte, len(before))
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for i := range before {
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prog[i] = byte(before[i])
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}
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raw := shortenJumps(prog, indices)
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actual := make([]opcode.Opcode, len(raw))
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for i := range raw {
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actual[i] = opcode.Opcode(raw[i])
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}
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require.Equal(t, after, actual)
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}
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func TestShortenJumps(t *testing.T) {
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testCases := map[opcode.Opcode]opcode.Opcode{
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opcode.JMPL: opcode.JMP,
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opcode.JMPIFL: opcode.JMPIF,
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opcode.JMPIFNOTL: opcode.JMPIFNOT,
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opcode.JMPEQL: opcode.JMPEQ,
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opcode.JMPNEL: opcode.JMPNE,
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opcode.JMPGTL: opcode.JMPGT,
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opcode.JMPGEL: opcode.JMPGE,
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opcode.JMPLEL: opcode.JMPLE,
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opcode.JMPLTL: opcode.JMPLT,
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opcode.CALLL: opcode.CALL,
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}
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for op, sop := range testCases {
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t.Run(op.String(), func(t *testing.T) {
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before := []opcode.Opcode{
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op, 6, 0, 0, 0, opcode.PUSH1, opcode.NOP, // <- first jump to here
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op, 9, 12, 0, 0, opcode.PUSH1, opcode.NOP, // <- last jump to here
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op, 255, 0, 0, 0, op, 0xFF - 5, 0xFF, 0xFF, 0xFF,
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}
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after := []opcode.Opcode{
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sop, 3, opcode.PUSH1, opcode.NOP,
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op, 3, 12, 0, 0, opcode.PUSH1, opcode.NOP,
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sop, 249, sop, 0xFF - 2,
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}
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testShortenJumps(t, before, after, []int{0, 14, 19})
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})
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}
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t.Run("NoReplace", func(t *testing.T) {
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b := []byte{0, 1, 2, 3, 4, 5}
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expected := []byte{0, 1, 2, 3, 4, 5}
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require.Equal(t, expected, shortenJumps(b, nil))
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})
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t.Run("InvalidIndex", func(t *testing.T) {
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before := []byte{byte(opcode.PUSH1), 0, 0, 0, 0}
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require.Panics(t, func() {
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shortenJumps(before, []int{0})
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})
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})
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t.Run("SideConditions", func(t *testing.T) {
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t.Run("Forward", func(t *testing.T) {
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before := []opcode.Opcode{
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opcode.JMPL, 5, 0, 0, 0,
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opcode.JMPL, 5, 0, 0, 0,
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}
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after := []opcode.Opcode{
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opcode.JMP, 2,
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opcode.JMP, 2,
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}
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testShortenJumps(t, before, after, []int{0, 5})
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})
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t.Run("Backwards", func(t *testing.T) {
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before := []opcode.Opcode{
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opcode.JMPL, 5, 0, 0, 0,
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opcode.JMPL, 0xFF - 4, 0xFF, 0xFF, 0xFF,
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opcode.JMPL, 0xFF - 4, 0xFF, 0xFF, 0xFF,
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}
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after := []opcode.Opcode{
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opcode.JMPL, 5, 0, 0, 0,
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opcode.JMP, 0xFF - 4,
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opcode.JMP, 0xFF - 1,
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}
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testShortenJumps(t, before, after, []int{5, 10})
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})
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})
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}
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func TestWriteJumps(t *testing.T) {
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c := new(codegen)
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c.l = []int{10}
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before := []byte{
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byte(opcode.NOP), byte(opcode.JMP), 2, byte(opcode.RET),
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byte(opcode.CALLL), 0, 0, 0, 0, byte(opcode.RET),
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byte(opcode.PUSH2), byte(opcode.RET),
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}
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c.funcs = map[string]*funcScope{
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"init": {rng: DebugRange{Start: 0, End: 3}},
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"main": {rng: DebugRange{Start: 4, End: 9}},
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"method": {rng: DebugRange{Start: 10, End: 11}},
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}
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expProg := []byte{
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byte(opcode.NOP), byte(opcode.JMP), 2, byte(opcode.RET),
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byte(opcode.CALL), 3, byte(opcode.RET),
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byte(opcode.PUSH2), byte(opcode.RET),
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}
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expFuncs := map[string]*funcScope{
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"init": {rng: DebugRange{Start: 0, End: 3}},
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"main": {rng: DebugRange{Start: 4, End: 6}},
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"method": {rng: DebugRange{Start: 7, End: 8}},
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}
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buf, err := c.writeJumps(before)
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require.NoError(t, err)
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require.Equal(t, expProg, buf)
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require.Equal(t, expFuncs, c.funcs)
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}
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