A Tale of TurboFan�Four years that changed V8 forever

Benedikt Meurer

@bmeurer

Overview

1. How does V8 work?
2. What is TurboFan?
3. The optimizing compiler in detail
4. Performance result

IGNITION

What is TurboFan?

• Modern code generation architecture for growing number of platforms (8+)
• Replacement for the aging Crankshaft compiler
• Optimizing compiler with full ES2015+ language support
• Predictable and consistent performance profile

launched in

​

​

and !

Unified code generation architecture

TurboFan code

generation

architecture

Intel, ARM, PowerPC,

MIPS

Control flow graph

TurboFan Optimizing Compiler

Bytecode

Inlining

Inlining

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

function three_add_inlined() {� var x = 1;

var y = 2;� var add_return_value = x + y;� return add_return_value;�}

function three_add_const_folded() {� return 3;�}

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Check x is a small integer

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Check x is a small integer

Check y is a small integer

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Check x is a small integer

Check y is a small integer

Convert y from tagged representation to word32

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Check x is a small integer

Check y is a small integer

Convert y from tagged representation to word32

Convert x from tagged representation to word32

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Check x is a small integer

Check y is a small integer

Convert y from tagged representation to word32

Convert x from tagged representation to word32

Add x and y (incl. overflow check)

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Check x is a small integer

Check y is a small integer

Convert y from tagged representation to word32

Convert x from tagged representation to word32

Add x and y (incl. overflow check)

Convert result to tagged representation

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Check x is a small integer

Check y is a small integer

Convert y from tagged representation to word32

Convert x from tagged representation to word32

Add x and y (incl. overflow check)

Convert result to tagged representation

Epilogue

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rdi,<JSFunction add>�movq rsi,[rdi+0x1f]�movq rax,<JSGlobal Object>�push rax�movq rax,0x100000000�push rax�movq rax,0x200000000�push rax�movq rdx,[r13-0x60]�movl rax,0x2�movq rcx,[rdi+0x2f]�addq rcx,0x5f�call rcx�movq rsp,rbp�pop rbp�ret 0x8

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rdi,<JSFunction add>�movq rsi,[rdi+0x1f]�movq rax,<JSGlobal Object>�push rax�movq rax,0x100000000�push rax�movq rax,0x200000000�push rax�movq rdx,[r13-0x60]�movl rax,0x2�movq rcx,[rdi+0x2f]�addq rcx,0x5f�call rcx�movq rsp,rbp�pop rbp�ret 0x8

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rdi,<JSFunction add>�movq rsi,[rdi+0x1f]�movq rax,<JSGlobal Object>�push rax�movq rax,0x100000000�push rax�movq rax,0x200000000�push rax�movq rdx,[r13-0x60]�movl rax,0x2�movq rcx,[rdi+0x2f]�addq rcx,0x5f�call rcx�movq rsp,rbp�pop rbp�ret 0x8

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Load call target add

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rdi,<JSFunction add>�movq rsi,[rdi+0x1f]�movq rax,<JSGlobal Object>�push rax�movq rax,0x100000000�push rax�movq rax,0x200000000�push rax�movq rdx,[r13-0x60]�movl rax,0x2�movq rcx,[rdi+0x2f]�addq rcx,0x5f�call rcx�movq rsp,rbp�pop rbp�ret 0x8

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Load call target add

Load call parameters

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rdi,<JSFunction add>�movq rsi,[rdi+0x1f]�movq rax,<JSGlobal Object>�push rax�movq rax,0x100000000�push rax�movq rax,0x200000000�push rax�movq rdx,[r13-0x60]�movl rax,0x2�movq rcx,[rdi+0x2f]�addq rcx,0x5f�call rcx�movq rsp,rbp�pop rbp�ret 0x8

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Load call target add

Load call parameters

Call sequence

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rdi,<JSFunction add>�movq rsi,[rdi+0x1f]�movq rax,<JSGlobal Object>�push rax�movq rax,0x100000000�push rax�movq rax,0x200000000�push rax�movq rdx,[r13-0x60]�movl rax,0x2�movq rcx,[rdi+0x2f]�addq rcx,0x5f�call rcx�movq rsp,rbp�pop rbp�ret 0x8

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

Load call target add

Load call parameters

Call sequence

Epilogue

Prologue

Inlining

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,0x300000000�movq rsp,rbp�pop rbp�ret 0x8

Inlining

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,0x300000000�movq rsp,rbp�pop rbp�ret 0x8

Prologue

Inlining

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,0x300000000�movq rsp,rbp�pop rbp�ret 0x8

Load tagged value 3

Prologue

Inlining

function add(x, y) {

return x + y;�}

�function three() {� return add(1, 2);�}

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,0x300000000�movq rsp,rbp�pop rbp�ret 0x8

Load tagged value 3

Epilogue

Prologue

Inlining

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,0x300000000�movq rsp,rbp�pop rbp�ret 0x8

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rdi,<JSFunction add>�movq rsi,[rdi+0x1f]�movq rax,<JSGlobal Object>�push rax�movq rax,0x100000000�push rax�movq rax,0x200000000�push rax�movq rdx,[r13-0x60]�movl rax,0x2�movq rcx,[rdi+0x2f]�addq rcx,0x5f�call rcx�movq rsp,rbp�pop rbp�ret 0x8

leaq rcx,[rip+0x0]�movq rcx,[rcx-0x37]�testb [rcx+0xf],0x1�jnz CompileLazyDeoptimizedCode�push rbp�movq rbp,rsp�push rsi�push rdi�cmpq rsp,[r13+0xdb0]�jna StackCheck�movq rax,[rbp+0x18]�test al,0x1�jnz Deoptimize�movq rbx,[rbp+0x10]�testb rbx,0x1�jnz Deoptimize�movq rdx,rbx�shrq rdx, 32�movq rcx,rax�shrq rcx, 32�addl rdx,rcx�jo Deoptimize�shlq rdx, 32�movq rax,rdx�movq rsp,rbp�pop rbp�ret 0x18

+

vs

Inlining

• Crucial to reduce small function overhead
• Not just in JavaScript!
• Makes other optimizations more effective
• Constant folding
• Strength reduction
• Redundancy elimination
• Escape analysis / scalar replacement of aggregates

Escape Analysis and Scalar Replacement

​

Escape Analysis and Scalar Replacement

• Avoid allocating local objects in the heap
• Escape Analysis determines whether the lifetime of an object can be proven to be restricted only to the current function
• Object is allocated inside that function
• Object doesn’t escape the function
• If an object is found to be accessed in ways that do not require the object to exist as a sequential memory structure, Scalar Replacement may allow its fields be stored in CPU registers instead of in memory

Escape Analysis and Scalar Replacement

class Point {� constructor(x, y) {

this.x = x;

this.y = y;� }�� distance(that) {� return Math.abs(this.x - that.x)� + Math.abs(this.y - that.y);� }�}��function manhattan(x1, y1, x2, y2) {� const a = new Point(x1, y1);� const b = new Point(x2, y2);� return a.distance(b);�}

function manhattan_inl(x1, y1, x2, y2) {� const a = {x:x1, y:y1};� const b = {x:x2, y:y2};� return Math.abs(a.x - b.x)� + Math.abs(a.y - b.y);�}

Escape Analysis and Scalar Replacement

function manhattan_inl(x1, y1, x2, y2) {� const a = {x:x1, y:y1};� const b = {x:x2, y:y2};� return Math.abs(a.x - b.x)� + Math.abs(a.y - b.y);�}

Over-simplified conditions for non escaping objects:

1. Allocated inside the function (after inlining)
2. All uses are property accesses
• Not returned from the function
• Not yielded
• Not passed to non-inlined function
• Not referenced from an escaping object

Escape Analysis and Scalar Replacement

function manhattan_inl(x1, y1, x2, y2) {� const a = {x:x1, y:y1};� const b = {x:x2, y:y2};� return Math.abs(a.x - b.x)� + Math.abs(a.y - b.y);�}

function manhattan_ea(x1, y1, x2, y2) {� var a_x = x1;� var a_y = y1;� var b_x = x2;� var b_y = y2;� return Math.abs(a_x - b_x)� + Math.abs(a_y - b_y);�}

Map fields to local variables

Benefits:

• No need for allocation or costly property accesses anymore!
• Happens under the hood!

Example: Rest Parameters

function count(...args) {� return args.length;�}

Example: Rest Parameters

function count(...args) {� return args.length;�}

leaq rcx,[rip+0x0]� movq rcx,[rcx-0x37]� testb [rcx+0xf],0x1� jnz CompileLazyDeoptimizedCode� push rbp� movq rbp,rsp� push rsi� push rdi� cmpq rsp,[r13+0xdb0]� jna StackCheck� movq rax,rbp� movq rbx,[rax]� cmpq [rbx-0x8],0x20� jz L0� movq rbx,rax�L0: cmpq rax,rbx� jz L1� movq rax,[rbx-0x18]� cmpq rax,0x0� jge L2�L1: xorl rax, rax�L2: movq rsp,rbp� pop rbp� ret 0x8

​

Example: Rest Parameters

function count(...args) {� return args.length;�}

leaq rcx,[rip+0x0]� movq rcx,[rcx-0x37]� testb [rcx+0xf],0x1� jnz CompileLazyDeoptimizedCode� push rbp� movq rbp,rsp� push rsi� push rdi� cmpq rsp,[r13+0xdb0]� jna StackCheck� movq rax,rbp� movq rbx,[rax]� cmpq [rbx-0x8],0x20� jz L0� movq rbx,rax�L0: cmpq rax,rbx� jz L1� movq rax,[rbx-0x18]� cmpq rax,0x0� jge L2�L1: xorl rax, rax�L2: movq rsp,rbp� pop rbp� ret 0x8

​

Prologue

Example: Rest Parameters

function count(...args) {� return args.length;�}

leaq rcx,[rip+0x0]� movq rcx,[rcx-0x37]� testb [rcx+0xf],0x1� jnz CompileLazyDeoptimizedCode� push rbp� movq rbp,rsp� push rsi� push rdi� cmpq rsp,[r13+0xdb0]� jna StackCheck� movq rax,rbp� movq rbx,[rax]� cmpq [rbx-0x8],0x20� jz L0� movq rbx,rax�L0: cmpq rax,rbx� jz L1� movq rax,[rbx-0x18]� cmpq rax,0x0� jge L2�L1: xorl rax, rax�L2: movq rsp,rbp� pop rbp� ret 0x8

​

Prologue

Find the parameters

Example: Rest Parameters

function count(...args) {� return args.length;�}

leaq rcx,[rip+0x0]� movq rcx,[rcx-0x37]� testb [rcx+0xf],0x1� jnz CompileLazyDeoptimizedCode� push rbp� movq rbp,rsp� push rsi� push rdi� cmpq rsp,[r13+0xdb0]� jna StackCheck� movq rax,rbp� movq rbx,[rax]� cmpq [rbx-0x8],0x20� jz L0� movq rbx,rax�L0: cmpq rax,rbx� jz L1� movq rax,[rbx-0x18]� cmpq rax,0x0� jge L2�L1: xorl rax, rax�L2: movq rsp,rbp� pop rbp� ret 0x8

​

Prologue

Find the parameters

Count the number of parameters

Example: Rest Parameters

function count(...args) {� return args.length;�}

leaq rcx,[rip+0x0]� movq rcx,[rcx-0x37]� testb [rcx+0xf],0x1� jnz CompileLazyDeoptimizedCode� push rbp� movq rbp,rsp� push rsi� push rdi� cmpq rsp,[r13+0xdb0]� jna StackCheck� movq rax,rbp� movq rbx,[rax]� cmpq [rbx-0x8],0x20� jz L0� movq rbx,rax�L0: cmpq rax,rbx� jz L1� movq rax,[rbx-0x18]� cmpq rax,0x0� jge L2�L1: xorl rax, rax�L2: movq rsp,rbp� pop rbp� ret 0x8

​

Prologue

Find the parameters

Count the number of parameters

Epilogue

Example: Rest Parameters

function count(...args) {� return args.length;�}

leaq rcx,[rip+0x0]� movq rcx,[rcx-0x37]� testb [rcx+0xf],0x1� jnz CompileLazyDeoptimizedCode� push rbp� movq rbp,rsp� push rsi� push rdi� cmpq rsp,[r13+0xdb0]� jna StackCheck� movq rax,rbp� movq rbx,[rax]� cmpq [rbx-0x8],0x20� jz L0� movq rbx,rax�L0: cmpq rax,rbx� jz L1� movq rax,[rbx-0x18]� cmpq rax,0x0� jge L2�L1: xorl rax, rax�L2: movq rsp,rbp� pop rbp� ret 0x8

​

Prologue

Find the parameters

Count the number of parameters

Epilogue

Array args is never materialized!

Escape Analysis and Scalar Replacement

• Reduces pressure on the garbage collector (GC)
• Important optimization for a number of ES2015+ features
• Rest parameters
• for..of loops
• Destructuring
• Makes other optimizations more effective
• Constant folding
• Strength reduction
• Representation Selection
• Instruction Selection

Predictable

Performance

Performance cliffs in Crankshaft

(function good() {� const start = Date.now();� for (var i = 0; i < 1e8; i++) {}� console.log(Date.now() - start);�})();

(function bad() {� const start = Date.now();� for (var i = 0; i < 1e8; i++) {}� console.log(Date.now() - start);� const whatever = 1;�})();

Runs ~80ms

Runs ~230ms

~3x slowdown�with Crankshaft

Optimization Killers

Optimization Killers

• Generators and async functions
• for-of and destructuring
• try-catch and try-finally
• Compound let or const assignment
• Object literals that contain __proto__, or get or set declarations.
• debugger or with statements
• Literal calls to eval()
• …

​

​

​

It’s not just�optimized code...

TypeScript 2.1.6 compiling itself

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Performance Results

60% faster web developer tools

v8project.blogspot.com/2017/11/web-tooling-benchmark.html

1.7× faster on ARES-6

browserbench.org/ARES-6

twitter.com/popeindustries/status/895575424406867968

Takeaways

• Write modern, idiomatic JavaScript
• Let us worry about making it fast

Follow us!

@v8js

Benedikt Meurer�@bmeurer

Thanks!��AMA on V8 & JS Performance�Tuesday 16:00–17:00, Room B