static optimization of php bytecode (phpsc 2017)
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Static Optimizationof
PHP BytecodeNikita Popov
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192 196212
476 486501
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PHP 5.3 PHP 5.4 PHP 5.5 PHP 5.6 PHP 7.0 PHP 7.1 PHP 7.2
Req
/ S
ec
Stolen from Rasmus
Wordpress 4.8-alpha @ 20c
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154
192 196212
476 486501
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
/ S
ec
Stolen from Rasmus
Wordpress 4.8-alpha @ 20c
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$a = 42;$b = 24;echo $a + $b;
Code
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ASSIGN $a, 42ASSIGN $b, 24
T0 = ADD $a, $bECHO T0
$a = 42;$b = 24;echo $a + $b;
Compile
CodeOpcodes
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ASSIGN $a, 42ASSIGN $b, 24
T0 = ADD $a, $bECHO T0
$a = 42;$b = 24;echo $a + $b;
Compile VirtualMachine
Execute
CodeOpcodes
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ASSIGN $a, 42ASSIGN $b, 24
T0 = ADD $a, $bECHO T0
$a = 42;$b = 24;echo $a + $b;
Compile VirtualMachine
Execute
CodeOpcodes
Optimize
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ASSIGN $a, 42ASSIGN $b, 24
T0 = ADD $a, $bECHO T0
$a = 42;$b = 24;echo $a + $b;
Compile VirtualMachine
Execute
CodeOpcodes
Optimize
SSA
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Optimizations
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$c = $a + $b;
T0 = ADD $a, $bASSIGN $c, T0
Optimizations
Specialization
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$c = $a + $b;
T0 = ADD $a, $bASSIGN $c, T0
$c = ADD $a, $b
Optimizations
Specialization
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$c = $a + $b;
T0 = ADD $a, $bASSIGN $c, T0
$c = ADD $a, $b
$c = ADD_INT $a, $b
Optimizations
Specialization
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$c = $a + $b;
T0 = ADD $a, $bASSIGN $c, T0
$c = ADD $a, $b
$c = ADD_INT $a, $b
$c = ADD_INT_NO_OVERFLOW $a, $b
Optimizations
Specialization
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Optimizations
Constant Propagation
$a = 2;$b = $a + 1;echo $a * $b;
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Optimizations
Constant Propagation
$a = 2;$b = 3;echo 6;
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Optimizations
Constant Propagation & Dead Code Elimination
echo 6;
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Optimizations
Inlining
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Optimizations
Inlining
function test() {var_dump(div(4, 2));
}
function div($a, $b) {if ($b == 0) {
return -1;}return $a / $b;
}
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Optimizations
Inlining
function test() {var_dump(div(4, 2));
}
function div($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);
}
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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, $b);var_dump(2);
}
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Optimizations
Inlining + CP + DCE
function test() {var_dump(div(4, 2));
}
function div($a, $b) {if ($b == 0) {
return -1;}return $a / $b;
}
function test() {
var_dump(2);}
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SSA Formand
Type Inference
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$x = 42;if (cond) {
$x = 42.0;var_dump($x);
} else {$x = "42";var_dump($x);
}
var_dump($x);
Static Single Assignment (SSA) Form
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$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 $x:int|float|string
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$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 $x here:float|string
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$x = 42;if (cond) {
$x = 42.0;var_dump($x);
} else {$x = "42";var_dump($x);
}
var_dump($x);
Static Single Assignment (SSA) Form
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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_?);
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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);
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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);
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Type Inference
$x = 42;do {
$y = $x;$x = $x + 3.14;
} while (cond);
var_dump($y);
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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);
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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);
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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 : ∅
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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 : ∅
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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 : ∅
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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 : ∅
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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
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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
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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
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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
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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
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Type Inference
$a = 2**62;$b = 2**62;var_dump($a + $b);// float(9.2233720368548E+18)
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Type Inference
$a = 2**62;$b = 2**62;var_dump($a + $b);// float(9.2233720368548E+18)
Accurate type inference requires value range inference!
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Type Inference
$a = 2**62;$b = 2**62;var_dump($a + $b);// float(9.2233720368548E+18)
Accurate type inference requires value range inference!
Same basic concept as type inference,but technically more involved…
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Optimization obstacles
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eval()?
variable variables?
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eval()?
variable variables?
Don't optimize functions using those!
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function test() {$foobar = 42;func($foobar);var_dump($foobar); // int(42)?
}
References
function func(&$ref) {$ref = 24;
}
function test() {$foobar = 42;func($foobar);var_dump($foobar); // int(42)? nope!
}
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References
// file1.phpfunction func(&$ref) {
$ref = 24;}
// file2.phpfunction test() {
$foobar = 42;func($foobar);var_dump($foobar); // int(42)? nope!
}
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References
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References
Files compiledindependently
// file1.phpfunction func(&$ref) {
$ref = 24;}
// file2.phpfunction test() {
$foobar = 42;func($foobar);var_dump($foobar); // int(42)? nope!
}
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The devil is in the details…
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$a = 1;$b = 1;var_dump($a + $b); // ???
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// file1.php$a = 1;$b = 1;var_dump($a + $b); // ???
// file2.php// EVIL CODE HERErequire 'file1.php';
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// file1.php$a = 1;$b = 1;var_dump($a + $b); // ???
// file2.php$b = new class {
function __destruct() {$GLOBALS['b'] = 2;
}};require 'file1.php'; // int(3)
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Pseudo-main scope is a lost cause!
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function test() {$obj = new stdClass;$obj->prop = 42;// Code not using $obj in any wayvar_dump($obj->prop); // ???
}
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function test() {$obj = new stdClass;$obj->prop = 42;// Code not using $obj in any wayvar_dump($obj->prop); // ???
}
set_error_handler(function($_1, $_2, $_3, $_4, $scope) {$scope['obj']->prop = "foobar";
});
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function test() {$obj = new stdClass;$obj->prop = 42;// Code not using $obj in any wayvar_dump($obj->prop); // ???
}
set_error_handler(function($_1, $_2, $_3, $_4, $scope) {$scope['obj']->prop = "foobar";
});
Could generate warning
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function test() {$obj = new stdClass;$obj->prop = 42;// Code not using $obj in any wayvar_dump($obj->prop); // ???
}
set_error_handler(function($_1, $_2, $_3, $_4, $scope) {$scope['obj']->prop = "foobar";
});
Could generate warning
95% of instructions havesome error condition
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Object properties (and references)are a lost cause :(
• Constant Propagation, Dead Code Elimination, etc. only really effective with inlining
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Inlining
• 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
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Inlining
• 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
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Inlining
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Results
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Results (microbenchmarks)
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Results (libraries/applications)
• phpseclib RSA enc/dec: 18%
• Aerys Huffman coding: 8%
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Results (libraries/applications)
• phpseclib RSA enc/dec: 18%
• Aerys Huffman coding: 8%
• WordPress: 3%
• MediaWiki: 1%
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Type Inference Stats
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State
• SSA + Type Inference in PHP 7.1
• Specialization in PHP 7.1
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State
• SSA + Type Inference in PHP 7.1
• Specialization in PHP 7.1
• Inlining, Constant Propagation, DCE, etc. not in PHP 7.1
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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
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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
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@nikita_ppv
https://joind.in/talk/57be5
Questions?
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