JDart. Rémi Forax JVM Summit'12

Transcription

1 JDart Rémi Forax JVM Summit'12

2 Dart in one slide Dynamic Language 2 runtimes : DartVM / Dart2js Less dynamic than Java? Better JavaScript Scope done right, classes, no_such_method, mirrors Optionally types types are mostly for documentation checked mode Integers are nullable and infinite

3 DartVM Derived from V8 Not a production VM (yet!) Client VM / 32 bits only Two tiers compiler Use tagged pointer (small integer/reference) Far better than Java boxing!

4 Example on Fibonacci int fibo(n) { return fibo(n-1) + fibo(n-2); main() { fibo(7);

5 In assembler simple code 0xf3108f0a 0xf3108f0d 0xf3108f12 0xf3108f17 0xf3108f1c 0xf3108f21 0xf3108f24 0xf3108f25 0xf3108f2a 0xf3108f2f 0xf3108f34 0xf3108f37 push [ebp+0x8] push 0x2 mov ecx,0xf31b8f11 'ICData target:-' mov edx,0xf331d279 Array[2, 2, null] call 0xf [stub: TwoArgsCheckInlineCache] add esp,0x8 push eax mov ecx,0xf31b8ca1 'Function 'fibo': static.' mov edx,0xf31a1ba9 Array[1, 1, null] call 0xf [stub: CallStaticFunction] add esp,0x4 push eax 0xf3108f38 push [ebp+0x8] 0xf3108f3b push 0x4... ; same code again! 0xf3108f66 mov ecx,0xf31b8fd1 'ICData target:+' 0xf3108f6b mov edx,0xf331d279 Array[2, 2, null] 0xf3108f70 call 0xf [stub: TwoArgsCheckInlineCache] 0xf3108f75 add esp,0x8 0xf3108f78 push eax 0xf3108f79 pop eax 0xf3108f7a mov ebx,0xf31b8ca1 'Function 'fibo': static.' 0xf3108f7f inc [ebx+0x43] 0xf3108f82 cmp [ebx+0x43],0x7d0 0xf3108f89 jng 0xf3108f9e

6 In assembler - optimized 0xf xf xf310900d 0xf310900f 0xf xf xf xf310901f 0xf xf xf310902a 0xf310902f 0xf mov eax,[ebp+0x8] mov edx,0x2 mov ecx,eax test al,0x1 jnz 0xf sub eax,edx jo 0xf push eax mov ecx,0xf31b8ca1 'Function 'fibo': static.' mov edx,0xf31a1ba9 Array[1, 1, null] call 0xf [stub: CallStaticFunction] add esp,0x4 push eax 0xf mov eax,[ebp+0x8] 0xf mov edx,0x4... ; same code again 0xf310905b mov ecx,eax 0xf310905d or eax,edx 0xf310905f test al,0x1 0xf jnz 0xf310909b 0xf mov eax,ecx 0xf add eax,edx 0xf310906b jo 0xf310909b 0xf mov esp,ebp 0xf pop ebp 0xf ret

7 Dart on the JVM Dart on server uses invokedynamic! but avoid useless boxing precise static type analysis (done offline currently) split-path trick

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9 JDart static analysis Use a linear* interprocedural type flow analysis before generating bytecode Don't use declared type by default Can be used in rare cases in checked mode Works with an horizon, try to share/reuse analysis Analysis not done more than K times by method (actually K=4) * almost :)

10 Example on Fibonacci int fibo(n [7]) { return fibo(n -1 [6]) + fibo(n-2); main() { fibo(7);

11 Example on Fibonacci int fibo(n [7]) { return fibo(n -1 [6]) + fibo(n-2); int fibo(n [0, +inf]) { // return type [1] return fibo(n [2, +inf] -1) + fibo(n-2); main() { fibo(7);

12 Example on Fibonacci int fibo(n [7]) { return fibo(n -1 [6]) + fibo(n-2); int fibo(n [0, +inf]) { // return type = [1] return [-inf, +inf]? + fibo(n-2 [0, +inf]); // return type = [-inf, +inf] main() { fibo(7);

13 Example on Fibonacci int fibo(n [7]) { return fibo(n -1 [6]) [-inf, +inf] + fibo(n-2 [5]) [-inf, +inf]; [-inf, +inf] int fibo(n [0, +inf]) { // return type = [1] return [-inf, +inf]? + fibo(n-2 [0, +inf]); // return type = [-inf, +inf] main() { fibo(7);

14 Example on Fibonacci [-inf, +inf] int fibo(n [7]) { return fibo(n -1 [6]) [-inf, +inf] + fibo(n-2) [-inf, +inf]; [-inf, +inf] int fibo(n [0, +inf]) { // return type = [1] return [-inf, +inf]? + fibo(n-2 [0, +inf]); // return type = [-inf, +inf] main() { fibo(7); We can remove the first fibo because fibo([7]) doesn't offer a more precise return type

15 Split-path generation Methods that takes an int > int32 are compiled in two methods If return type is int, int32 will be used and overflow values will use a thread local exception In the method, ints are compiled using two variables (int32 and BigInt) if BigInt is null, value is int32 Overflow detection is added where needed using the profile

16 Fibo in pseudo Java private static int fibo(int n) { int r1; BigInt _r1; try { r1 = invokedynamic fibo(n -1); _r1 = null; catch(controlflowexception e) { r1 = 0; _r1 = e.value; int r2; BigInt _r2; try { r2 = invokedynamic fibo(n -2); _r2 = null; catch(controlflowexception e) { r2 = 0; _r2 = e.value; int r3; BigInt _r3; if (_r1 == null && _r2 == null) try { r3 = RT.addExact(r1, r2); _r3 = null; catch(arithmeticexception e) { _r3 = invokedynamic addoverflowed(r1, r2); r3 = 0; else _r3 = invokedynamic addbig(r1, _r1, r2, _r2); r3 = 0; if (_r3 == null) return r3; throw ControlFlowException.valueOf(_r3);

17 In assembler...fd4c: mov %esi,(%rsp)...fd4f: cmp $0x2,%esi...fd52: jl...fda1 ;*if_icmpge...fd54: dec %esi ;*isub...fd57: callq 0x00007f ;*invokestatic fibo...fd5c: mov %eax,0x4(%rsp)...fd60: mov (%rsp),%esi...fd63: add $0xfffffffffffffffe,%esi ;*isub...fd67: callq 0x00007f ;*invokestatic fibo...fd6c: mov %eax,%r9d...fd6f: mov 0x4(%rsp),%eax...fd73: add %r9d,%eax...fd76: mov 0x4(%rsp),%r11d...fd7b: xor %eax,%r11d...fd7e: mov %r9d,%r8d...fd81: xor %eax,%r8d...fd84: and %r8d,%r11d...fd87: test %r11d,%r11d...fd8a: jge...fda6 ;inline RT.addExact...fd8c: mov $0xa5,%esi...fd91: mov %r9d,(%rsp)...fd95: xchg %ax,%ax...fd97: callq 0x00007f ; deoptimization...fda1: mov $0x1,%eax fast path??

18 Execution time! Fibo(40) in second JDart (no inline) JDart Java (int only) 0 DartVM Smaller is better Java boxing

19 Questions?

20 Image Credits Phone booth by Louis du Mons Overflow by James Whitesmith