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[R4R]core/vm: faster code analysis (#23381) #379

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Aug 24, 2021
Merged

[R4R]core/vm: faster code analysis (#23381) #379

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94 changes: 78 additions & 16 deletions core/vm/analysis.go
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Original file line number Diff line number Diff line change
Expand Up @@ -16,17 +16,49 @@

package vm

const (
set2BitsMask = uint16(0b1100_0000_0000_0000)
set3BitsMask = uint16(0b1110_0000_0000_0000)
set4BitsMask = uint16(0b1111_0000_0000_0000)
set5BitsMask = uint16(0b1111_1000_0000_0000)
set6BitsMask = uint16(0b1111_1100_0000_0000)
set7BitsMask = uint16(0b1111_1110_0000_0000)
)

// bitvec is a bit vector which maps bytes in a program.
// An unset bit means the byte is an opcode, a set bit means
// it's data (i.e. argument of PUSHxx).
type bitvec []byte

func (bits *bitvec) set(pos uint64) {
(*bits)[pos/8] |= 0x80 >> (pos % 8)
var lookup = [8]byte{
0x80, 0x40, 0x20, 0x10, 0x8, 0x4, 0x2, 0x1,
}

func (bits bitvec) set1(pos uint64) {
bits[pos/8] |= lookup[pos%8]
}

func (bits bitvec) setN(flag uint16, pos uint64) {
a := flag >> (pos % 8)
bits[pos/8] |= byte(a >> 8)
if b := byte(a); b != 0 {
// If the bit-setting affects the neighbouring byte, we can assign - no need to OR it,
// since it's the first write to that byte
bits[pos/8+1] = b
}
}

func (bits bitvec) set8(pos uint64) {
a := byte(0xFF >> (pos % 8))
bits[pos/8] |= a
bits[pos/8+1] = ^a
}
func (bits *bitvec) set8(pos uint64) {
(*bits)[pos/8] |= 0xFF >> (pos % 8)
(*bits)[pos/8+1] |= ^(0xFF >> (pos % 8))

func (bits bitvec) set16(pos uint64) {
a := byte(0xFF >> (pos % 8))
bits[pos/8] |= a
bits[pos/8+1] = 0xFF
bits[pos/8+2] = ^a
}

// codeSegment checks if the position is in a code segment.
Expand All @@ -40,22 +72,52 @@ func codeBitmap(code []byte) bitvec {
// ends with a PUSH32, the algorithm will push zeroes onto the
// bitvector outside the bounds of the actual code.
bits := make(bitvec, len(code)/8+1+4)
return codeBitmapInternal(code, bits)
}

// codeBitmapInternal is the internal implementation of codeBitmap.
// It exists for the purpose of being able to run benchmark tests
// without dynamic allocations affecting the results.
func codeBitmapInternal(code, bits bitvec) bitvec {
for pc := uint64(0); pc < uint64(len(code)); {
op := OpCode(code[pc])

if op >= PUSH1 && op <= PUSH32 {
numbits := op - PUSH1 + 1
pc++
pc++
if op < PUSH1 || op > PUSH32 {
continue
}
numbits := op - PUSH1 + 1
if numbits >= 8 {
for ; numbits >= 16; numbits -= 16 {
bits.set16(pc)
pc += 16
}
for ; numbits >= 8; numbits -= 8 {
bits.set8(pc) // 8
bits.set8(pc)
pc += 8
}
for ; numbits > 0; numbits-- {
bits.set(pc)
pc++
}
} else {
pc++
}
switch numbits {
case 1:
bits.set1(pc)
pc += 1
case 2:
bits.setN(set2BitsMask, pc)
pc += 2
case 3:
bits.setN(set3BitsMask, pc)
pc += 3
case 4:
bits.setN(set4BitsMask, pc)
pc += 4
case 5:
bits.setN(set5BitsMask, pc)
pc += 5
case 6:
bits.setN(set6BitsMask, pc)
pc += 6
case 7:
bits.setN(set7BitsMask, pc)
pc += 7
}
}
return bits
Expand Down
24 changes: 22 additions & 2 deletions core/vm/analysis_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -47,10 +47,10 @@ func TestJumpDestAnalysis(t *testing.T) {
{[]byte{byte(PUSH32)}, 0xFF, 1},
{[]byte{byte(PUSH32)}, 0xFF, 2},
}
for _, test := range tests {
for i, test := range tests {
ret := codeBitmap(test.code)
if ret[test.which] != test.exp {
t.Fatalf("expected %x, got %02x", test.exp, ret[test.which])
t.Fatalf("test %d: expected %x, got %02x", i, test.exp, ret[test.which])
}
}
}
Expand All @@ -73,3 +73,23 @@ func BenchmarkJumpdestHashing_1200k(bench *testing.B) {
}
bench.StopTimer()
}

func BenchmarkJumpdestOpAnalysis(bench *testing.B) {
var op OpCode
bencher := func(b *testing.B) {
code := make([]byte, 32*b.N)
for i := range code {
code[i] = byte(op)
}
bits := make(bitvec, len(code)/8+1+4)
b.ResetTimer()
codeBitmapInternal(code, bits)
}
for op = PUSH1; op <= PUSH32; op++ {
bench.Run(op.String(), bencher)
}
op = JUMPDEST
bench.Run(op.String(), bencher)
op = STOP
bench.Run(op.String(), bencher)
}
4 changes: 4 additions & 0 deletions core/vm/instructions.go
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Original file line number Diff line number Diff line change
Expand Up @@ -669,6 +669,7 @@ func opCall(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([]byt
}
stack.push(&temp)
if err == nil || err == ErrExecutionReverted {
ret = common.CopyBytes(ret)
scope.Memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
}
scope.Contract.Gas += returnGas
Expand Down Expand Up @@ -703,6 +704,7 @@ func opCallCode(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext) ([
}
stack.push(&temp)
if err == nil || err == ErrExecutionReverted {
ret = common.CopyBytes(ret)
scope.Memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
}
scope.Contract.Gas += returnGas
Expand Down Expand Up @@ -730,6 +732,7 @@ func opDelegateCall(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext
}
stack.push(&temp)
if err == nil || err == ErrExecutionReverted {
ret = common.CopyBytes(ret)
scope.Memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
}
scope.Contract.Gas += returnGas
Expand Down Expand Up @@ -757,6 +760,7 @@ func opStaticCall(pc *uint64, interpreter *EVMInterpreter, scope *ScopeContext)
}
stack.push(&temp)
if err == nil || err == ErrExecutionReverted {
ret = common.CopyBytes(ret)
scope.Memory.Set(retOffset.Uint64(), retSize.Uint64(), ret)
}
scope.Contract.Gas += returnGas
Expand Down