This document discusses static optimization of PHP bytecode. It describes optimizations like constant propagation, dead code elimination, inlining, and specialization that have been implemented in PHP. It also discusses challenges to optimization from features like references, eval(), and variable variables. Type inference using static single assignment form is explained. Metrics on performance improvements from optimizations in libraries and applications like WordPress are provided. Current and future work on additional optimizations in PHP is mentioned.

1. Static Optimization
of
PHP Bytecode
Nikita Popov

2. 2
154
192 196
212
476 486
501
0
100
200
300
400
500
PHP 5.3 PHP 5.4 PHP 5.5 PHP 5.6 PHP 7.0 PHP 7.1 PHP 7.2
Req/Sec
Stolen from Rasmus
Wordpress 4.8-alpha @ 20c

3. 3
154
192 196
212
476 486
501
0
100
200
300
400
500
PHP 5.3 PHP 5.4 PHP 5.5 PHP 5.6 PHP 7.0 PHP 7.1 PHP 7.2
Req/Sec
Stolen from Rasmus
Wordpress 4.8-alpha @ 20c

4. 4
$a = 42;
$b = 24;
echo $a + $b;
Code

5. 5
ASSIGN $a, 42
ASSIGN $b, 24
T0 = ADD $a, $b
ECHO T0
$a = 42;
$b = 24;
echo $a + $b;
Compile
Code
Opcodes

6. 6
ASSIGN $a, 42
ASSIGN $b, 24
T0 = ADD $a, $b
ECHO T0
$a = 42;
$b = 24;
echo $a + $b;
Compile Virtual
Machine
Execute
Code
Opcodes

7. 7
ASSIGN $a, 42
ASSIGN $b, 24
T0 = ADD $a, $b
ECHO T0
$a = 42;
$b = 24;
echo $a + $b;
Compile Virtual
Machine
Execute
Code
Opcodes
Optimize

8. 8
ASSIGN $a, 42
ASSIGN $b, 24
T0 = ADD $a, $b
ECHO T0
$a = 42;
$b = 24;
echo $a + $b;
Compile Virtual
Machine
Execute
Code
Opcodes
Optimize
SSA

9. 9
Optimizations

10. 10
$c = $a + $b;
T0 = ADD $a, $b
ASSIGN $c, T0
Optimizations
Specialization

11. 11
$c = $a + $b;
T0 = ADD $a, $b
ASSIGN $c, T0
$c = ADD $a, $b
Optimizations
Specialization

12. 12
$c = $a + $b;
T0 = ADD $a, $b
ASSIGN $c, T0
$c = ADD $a, $b
$c = ADD_INT $a, $b
Optimizations
Specialization

13. 13
$c = $a + $b;
T0 = ADD $a, $b
ASSIGN $c, T0
$c = ADD $a, $b
$c = ADD_INT $a, $b
$c = ADD_INT_NO_OVERFLOW $a, $b
Optimizations
Specialization

14. 14
Optimizations
Constant Propagation
$a = 2;
$b = $a + 1;
echo $a * $b;

15. 15
Optimizations
Constant Propagation
$a = 2;
$b = 3;
echo 6;

16. 16
Optimizations
Constant Propagation & Dead Code Elimination
echo 6;

17. 17
Optimizations
Inlining

18. 18
Optimizations
Inlining
function test() {
var_dump(div(4, 2));
}
function div($a, $b) {
if ($b == 0) {
return -1;
}
return $a / $b;
}

19. 19
Optimizations
Inlining
function test() {
var_dump(div(4, 2));
}
function div($a, $b) {
if ($b == 0) {
return -1;
}
return $a / $b;
}
function test() {
$a = 4;
$b = 2;
if ($b == 0) {
$retval = -1;
goto end;
}
$retval = $a / $b;
goto end;
end:
unset($a, $b);
var_dump($retval);
}

20. 20
Optimizations
Inlining + CP
function test() {
var_dump(div(4, 2));
}
function div($a, $b) {
if ($b == 0) {
return -1;
}
return $a / $b;
}
function test() {
$a = 4;
$b = 2;
$retval = 2;
goto end;
end:
unset($a, $b);
var_dump(2);
}

21. 21
Optimizations
Inlining + CP + DCE
function test() {
var_dump(div(4, 2));
}
function div($a, $b) {
if ($b == 0) {
return -1;
}
return $a / $b;
}
function test() {
var_dump(2);
}

22. 22
SSA Form
and
Type Inference

23. 23
$x = 42;
if (cond) {
$x = 42.0;
var_dump($x);
} else {
$x = "42";
var_dump($x);
}
var_dump($x);
Static Single Assignment (SSA) Form

24. 24
$x = 42;
if (cond) {
$x = 42.0;
var_dump($x);
} else {
$x = "42";
var_dump($x);
}
var_dump($x);
Static Single Assignment (SSA) Form
Type of $x:
int|float|string

25. 25
$x = 42;
if (cond) {
$x = 42.0;
var_dump($x);
} else {
$x = "42";
var_dump($x);
}
var_dump($x);
Static Single Assignment (SSA) Form
Type of $x here:
int
Type of $x here:
float
Type of $x here:
string
Type of $x here:
float|string

26. 26
$x = 42;
if (cond) {
$x = 42.0;
var_dump($x);
} else {
$x = "42";
var_dump($x);
}
var_dump($x);
Static Single Assignment (SSA) Form

27. 27
Static Single Assignment (SSA) Form
$x_1 = 42;
if (cond) {
$x_2 = 42.0;
var_dump($x_2);
} else {
$x_3 = "42";
var_dump($x_3);
}
var_dump($x_?);

28. 28
Static Single Assignment (SSA) Form
$x_1 = 42;
if (cond) {
$x_2 = 42.0;
var_dump($x_2);
} else {
$x_3 = "42";
var_dump($x_3);
}
$x_4 = phi($x_2, $x_3);
var_dump($x_4);

29. 29
Static Single Assignment (SSA) Form
$x_1 : int
$x_2 : float
$x_3 : string
$x_4 : float|string
$x_1 = 42;
if (cond) {
$x_2 = 42.0;
var_dump($x_2);
} else {
$x_3 = "42";
var_dump($x_3);
}
$x_4 = phi($x_2, $x_3);
var_dump($x_4);

30. 30
Type Inference
$x = 42;
do {
$y = $x;
$x = $x + 3.14;
} while (cond);
var_dump($y);

31. 31
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);

32. 32
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);

33. 33
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : ∅
$y_1 : ∅
$x_3 : ∅

34. 34
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : ∅
$y_1 : ∅
$x_3 : ∅

35. 35
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : int
$y_1 : ∅
$x_3 : ∅

36. 36
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : int
$y_1 : ∅
$x_3 : ∅

37. 37
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : int
$y_1 : int
$x_3 : float

38. 38
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : int
$y_1 : int
$x_3 : float

39. 39
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : int|float
$y_1 : int
$x_3 : float

40. 40
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : int|float
$y_1 : int
$x_3 : float

41. 41
Type Inference
$x_1 = 42;
do {
$x_2 = phi($x_1, $x_3);
$y_1 = $x_2;
$x_3 = $x_2 + 3.14;
} while (cond);
var_dump($y_1);
$x_1 : int
$x_2 : int|float
$y_1 : int|float
$x_3 : float

42. 42
Type Inference
$a = 2**62;
$b = 2**62;
var_dump($a + $b);
// float(9.2233720368548E+18)

43. 43
Type Inference
$a = 2**62;
$b = 2**62;
var_dump($a + $b);
// float(9.2233720368548E+18)
Accurate type inference requires value range inference!

44. 44
Type Inference
$a = 2**62;
$b = 2**62;
var_dump($a + $b);
// float(9.2233720368548E+18)
Accurate type inference requires value range inference!
Same basic concept as type inference,
but technically more involved…

45. 45
Optimization obstacles

46. 46
eval()?
variable variables?

47. 47
eval()?
variable variables?
Don't optimize functions using those!

48. 48
function test() {
$foobar = 42;
func($foobar);
var_dump($foobar); // int(42)?
}
References

49. function func(&$ref) {
$ref = 24;
}
function test() {
$foobar = 42;
func($foobar);
var_dump($foobar); // int(42)? nope!
}
49
References

50. // file1.php
function func(&$ref) {
$ref = 24;
}
// file2.php
function test() {
$foobar = 42;
func($foobar);
var_dump($foobar); // int(42)? nope!
}
50
References

51. 51
References
Files compiled
independently
// file1.php
function func(&$ref) {
$ref = 24;
}
// file2.php
function test() {
$foobar = 42;
func($foobar);
var_dump($foobar); // int(42)? nope!
}

52. 52
The devil is in the details…

53. 53
$a = 1;
$b = 1;
var_dump($a + $b); // ???

54. 54
// file1.php
$a = 1;
$b = 1;
var_dump($a + $b); // ???
// file2.php
// EVIL CODE HERE
require 'file1.php';

55. 55
// file1.php
$a = 1;
$b = 1;
var_dump($a + $b); // ???
// file2.php
$b = new class {
function __destruct() {
$GLOBALS['b'] = 2;
}
};
require 'file1.php'; // int(3)

56. 56
Pseudo-main scope is a lost cause!

57. 57
function test() {
$obj = new stdClass;
$obj->prop = 42;
// Code not using $obj in any way
var_dump($obj->prop); // ???
}

58. 58
function test() {
$obj = new stdClass;
$obj->prop = 42;
// Code not using $obj in any way
var_dump($obj->prop); // ???
}
set_error_handler(function($_1, $_2, $_3, $_4, $scope) {
$scope['obj']->prop = "foobar";
});

59. 59
function test() {
$obj = new stdClass;
$obj->prop = 42;
// Code not using $obj in any way
var_dump($obj->prop); // ???
}
set_error_handler(function($_1, $_2, $_3, $_4, $scope) {
$scope['obj']->prop = "foobar";
});
Could generate warning

60. 60
function test() {
$obj = new stdClass;
$obj->prop = 42;
// Code not using $obj in any way
var_dump($obj->prop); // ???
}
set_error_handler(function($_1, $_2, $_3, $_4, $scope) {
$scope['obj']->prop = "foobar";
});
Could generate warning
95% of instructions have
some error condition

61. 61
Object properties (and references)
are a lost cause :(

62. • Constant Propagation, Dead Code Elimination, etc. only really
effective with inlining
62
Inlining

63. • Constant Propagation, Dead Code Elimination, etc. only really
effective with inlining
• Inlining only works if callee is known
• Only within single file (thanks opcache)
• Non-private/final instance methods can be overridden
63
Inlining

64. • Constant Propagation, Dead Code Elimination, etc. only really
effective with inlining
• Inlining only works if callee is known
• Only within single file (thanks opcache)
• Non-private/final instance methods can be overridden
• Backtraces change
64
Inlining

65. 65
Results

66. 66
Results (microbenchmarks)

67. 67
Results (libraries/applications)
• phpseclib RSA enc/dec: 18%
• Aerys Huffman coding: 8%

68. 68
Results (libraries/applications)
• phpseclib RSA enc/dec: 18%
• Aerys Huffman coding: 8%
• WordPress: 3%
• MediaWiki: 1%

69. 69
Type Inference Stats

70. 70
State
• SSA + Type Inference in PHP 7.1
• Specialization in PHP 7.1

71. 71
State
• SSA + Type Inference in PHP 7.1
• Specialization in PHP 7.1
• Inlining, Constant Propagation, DCE, etc. not in PHP 7.1

72. 72
State
• SSA + Type Inference in PHP 7.1
• Specialization in PHP 7.1
• Inlining, Constant Propagation, DCE, etc. not in PHP 7.1
• Currently work underway on dynasm JIT using SSA + type
inference framework

73. 73
State
• SSA + Type Inference in PHP 7.1
• Specialization in PHP 7.1
• Inlining, Constant Propagation, DCE, etc. not in PHP 7.1
• Currently work underway on dynasm JIT using SSA + type
inference framework
Nikita Popov, Biagio Cosenza, Ben Juurlink, and Dmitry Stogov.
Static optimization in PHP 7. In CC'17, pages 65-75. ACM, 2017.
http://nikic.github.io/pdf/cc17_static_optimization.pdf

74. 74
@nikita_ppv
https://joind.in/talk/57be5
Questions?