Hiphop php

HipHop Compiler for PHP
Transforming PHP into C++

HipHop Compiler Team
Facebook, Inc.
May 2010

Facebook 2010 (confidential)

PHP is easy to read

<?php

function tally($count) {
$sum = 0;
for ($i = 0; $i< $count; ++$i) {
$sum += $i;
}
return $sum;
}

print tally(10) . “n”;


PHP syntax is similar to C++/Java

<?php

class Tool extends Object {
public $name;

public use($target) {}
}

$tool = new Tool();
$tool->name = „hammer‟;
$tool->use($nail);


PHP Statements and Expressions

FunctionStatement,
ClassStatement,
InterfaceStatement, ExpressionList,
ClassVariable, AssignmentExpression,
ClassConstant, SimpleVariable,
MethodStatement, DynamicVariable,
StatementList, StaticMemberExpression,
BlockStatement, ArrayElementExpression,
IfBranchStatement, DynamicFunctionCall,
IfStatement, SimpleFunctionCall,
WhileStatement, ScalarExpression,
DoStatement, ObjectPropertyExpression,
ForStatement, ObjectMethodExpression,
SwitchStatement, ListAssignment,
CaseStatement, NewObjectExpression,
BreakStatement, UnaryOpExpression,
ContinueStatement, IncludeExpression,
ReturnStatement, BinaryOpExpression,
GlobalStatement, QOpExpression,
StaticStatement, ArrayPairExpression,
EchoStatement, ClassConstantExpression,
UnsetStatement, ParameterExpression,
ExpStatement, ModifierExpression,
ForEachStatement, ConstantExpression,
CatchStatement, EncapsListExpression,
TryStatement,
ThrowStatement,

PHP is weakly typed

<?php

$a = 12345;
$a = “hello”;
$a = array(12345, “hello”, array());
$a = new Object();

$c = $a + $b; // integer or array
$c = $a . $b; // implicit casting to strings


Core PHP library is small

- Most are in functional style
- ~200 to 500 basic functions

<?php

$len = strlen(“hello”); // C library
$ret = curl_exec($curl); // open source


PHP is easy to debug

<?php

function tally($count) {
$sum = 0;
for ($i = 0; $i< $count; ++$i) {
$sum += $i;
var_dump($sum);
}
return $sum;
}


PHP is easy to learn

 easy to read
 easy to write
 easy to debug

Hello, World!

PHP is slow 

http://shootout.alioth.debian.org/u64q/benchmark.ph
p?test=all&lang=all
50

40

30

20 CPU

10

0
C++ Java C# Erlang Python Perl PHP


Why is Zend Engine slow?

 Byte-code interpreter

 Dynamic symbol lookups

 functions, variables, constants
 class methods, properties, constants

 Weakly typing
 zval
 array()

Transforming PHP into C++

 g++ is a native code compiler

 static binding

 functions, variables, constants
 class methods, properties, constants

 type inference
 integers, strings, arrays, objects, variants
 struct, vector, map, array

Static Binding – Function Calls

<?php
$ret = foo($a);

// C++
Variant v_ret;
Variant v_a;

v_ret = f_foo(v_a);


Dynamic Function Calls

<?php
$func = „foo‟;
$ret = $func($a);

// C++
Variant v_ret;
Variant v_a;
String v_func;

V_func = “foo”;
v_ret = invoke(v_func, CREATE_VECTOR1(v_a));

Function Invoke Table

Variant invoke(CStrReffunc, CArrRefparams) {
int64 hash = hash_string(func);
switch (hash) {
case 1234:
if (func == “foo”) return foo(params[0])
}
throw FatalError(“function not found”);
}


Re-declared Functions

<?php
if ($condition) {
function foo($a) { return $a + 1;}
} else {
function foo($a) { return $a + 2;}
}
$ret = foo($a);

// C++
if (v_condition) {
g->i_foo = i_foo$$0;
} else {
g->i_foo = i_foo$$1;
}
g->i_foo(v_a);


Volatile Functions

<?php
if (!function_exists(„foo‟)) {
bar($a);
} else {
foo($a);
}
function foo($a) {}

// C++
if (f_function_exists(“foo”)) {
f_bar(v_a);
} else {
f_foo(v_a);
}
g->declareFunction(“foo”);


Static Binding – Variables

<?php
$foo = „hello‟;
function foo($a) {
global $foo;
$bar = $foo . $a;
return $bar;
}

// C++
String f_foo(CStrRefv_a) {
Variant &gv_foo = g->GV(foo);
String v_bar;
v_bar = concat(toString(gv_foo), v_a);
return v_bar;
}


GlobalVariables Class

class GlobalVariables : public SystemGlobals {
public:
// Direct Global Variables
Variant gv_foo;

// Indirect Global Variables for large compilation
enum _gv_enums {
gv_foo,
}
Variant gv[1];
};


Dynamic Variables

<?php
function foo() {
$b = 10;
$a = 'b';
echo($$a);
}

void f_foo() {
class VariableTable: public RVariableTable {
public:
int64 &v_b; String &v_a;
VariableTable(int64 &r_b, String &r_a) : v_b(r_b), v_a(r_a) {}
virtual Variant getImpl(const char *s) {
// hash – switch – strcmp
}
} variableTable(v_b, v_a);

echo(variableTable.get("b”));
}


Static Binding – Constants

<?php
define(„FOO‟, „hello‟);
echo FOO;

// C++
echo(“hello” /* FOO */);


Dynamic Constants

<?php
if ($condition) {
define(„FOO‟, „hello‟);
} else {
define(„FOO‟, „world‟);
}
echo FOO;

// C++
if (v_condition) {
g->declareConstant("FOO", g->k_FOO, "hello”);
} else {
g->declareConstant("FOO", g->k_FOO, "world”);
}
echo(toString(g->k_FOO));


Static Binding with Classes

 Class methods

 Class properties

 Class constants

 Re-declared classes

 Deriving from re-declared classes

 Volatile classes


Summary - Dynamic Symbol Lookup
Problem is nicely solved 

 Rule of 90-10

 Dynamic binding is a general form of static
binding
 Generated code is a super-set of static
binding and dynamic binding


Problem 2. Weakly Typing

 Type Inference

 Runtime Type Info (RTTI)-Guided Optimization

 Type Hints

 Strongly Typed Collection Classes


Type Coercions

Variant

Double String Array Object

Integer

Boolean


Type Inference Example

<?php
$a = 10;
$a = „string‟;

Variant v_a;


Why is strong type faster?

$a = $b + $c;

if (is_integer($b) &&is_integer($c)) {
$a = (int)$b + (int)$c;
} else if (is_array($b) &&is_array($c)) {
$a = array_merge((array)$b + (array)$c);
} else {
…
}

int64 v_a = v_b + v_c;

Type Inference Blockers

<?php
function foo() {
if ($success) return 10; // integer
return false; // doh‟
}

$arr[$a] = 10; // doh‟

++$a; // $a can be a string actually!

$a = $a + 1; // $a can become a double, ouch!


RTTI-Guided Optimization

<?php
function foo($x) {
...
}

foo(10);
foo(„test‟);

void foo(Variantx) {
...
}


Type Specialization Method 1

template<typename T>
void foo(Tx) {
// generate code with generic T (tough!)
}

-Pros: smaller generated code
-Cons: no type propagation



void foo(int64 x) {
// generate code assuming x is integer
}
// generate code assuming x is variant
}

-Pros: type propagation
-Cons: variant case is not optimized



void foo(int64 x) {
// generate code assuming x is integer
}
if (is_integer(x)) {
foo(x.toInt64()); return;
}
// generate code assuming x is variant
}

-Pros: optimized for integer case
-Cons: large code size


Type Hints

<?php
function foo(int$a) {
string $b;
}

class bar {
public array $c;
}

bar $d;


Strongly Typed Collection Classes

 That omnipotent “array” in PHP 

 Swapping out underlying implementation:
 Array escalation
 PHP classes:
 Vector
 Set
 Map: un-ordered
 Then Array: ordered map

Compiler Friendly Scripting Language

If all problems described here are
considered when designing a new
scripting language, will it run
faster than Java?


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