Status: Untriaged
Owner: ----
New issue 4353 by [email protected]: Inlining code containing an array
literal leads to a performance loss
https://code.google.com/p/v8/issues/detail?id=4353
Version: fc80f29a582b758d14aae864232624ca45e47ddc
OS: Linux
Architecture: IA32
There are two files attached. The only difference is that in the slow one,
a one-line function has been manually inlined:
1876c1876
< for (var t1 = Y.TreeIterator$(this.items._tree); t1.moveNext$0();)
---
for (var t1 = new Y.TreeIterator(this.items._tree, null, [],
null); t1.moveNext$0();)
This leads to a surprising performance loss:
$ ~/v8.git/v8/out/ia32.release/d8 fast.js
Iteration.tree.manual(RunTime): 167.78523489932886 us.
$ ~/v8.git/v8/out/ia32.release/d8 slow.js
Iteration.tree.manual(RunTime): 656.1679790026246 us.
I think this is a bug. It suggests that the reverse transformation
(manually abstracting an array literal into a helper function) would
sometimes be a big optimization.
Details: slow.js deoptimizes but fast.js does not:
$ ~/v8.git/v8/out/ia32.release/d8 --trace-deopt slow.js
[deoptimizing (DEOPT eager): begin 0x57642411 <JS Function
dart.TreeIterator.moveNext$0 (SharedFunctionInfo 0x252949e9)> (opt #27) @6,
FP to SP delta: 28]
;;; deoptimize at 68012: wrong map
reading input frame dart.TreeIterator.moveNext$0 => node=1, args=142,
height=3; inputs:
0: 0x57642411 ; (frame function) 0x57642411 <JS Function
dart.TreeIterator.moveNext$0 (SharedFunctionInfo 0x252949e9)>
1: 0x5205ddf9 ; ecx 0x5205ddf9 <a TreeIterator with map 0x3771480d>
2: 0x57619789 ; [fp - 16] 0x57619789 <FixedArray[17]>
3: 0x5205d129 ; eax 0x5205d129 <a Node with map 0x37714261>
4: 0x5205dde1 ; edx 0x5205dde1 <JS Array[0]>
translating frame dart.TreeIterator.moveNext$0 => node=142, height=8
0xffb7c0e8: [top + 24] <- 0x5205ddf9 ; 0x5205ddf9 <a TreeIterator with
map 0x3771480d> (input #1)
0xffb7c0e4: [top + 20] <- 0x5e72f730 ; caller's pc
0xffb7c0e0: [top + 16] <- 0xffb7c0fc ; caller's fp
0xffb7c0dc: [top + 12] <- 0x57619789 ; context 0x57619789
<FixedArray[17]> (input #2)
0xffb7c0d8: [top + 8] <- 0x57642411 ; function 0x57642411 <JS
Function dart.TreeIterator.moveNext$0 (SharedFunctionInfo 0x252949e9)>
(input #0)
0xffb7c0d4: [top + 4] <- 0x5205d129 ; 0x5205d129 <a Node with map
0x37714261> (input #3)
0xffb7c0d0: [top + 0] <- 0x5205dde1 ; 0x5205dde1 <JS Array[0]> (input
#4)
[deoptimizing (eager): end 0x57642411 <JS Function
dart.TreeIterator.moveNext$0 (SharedFunctionInfo 0x252949e9)> @6 =>
node=142, pc=0x5e71bbcc, state=NO_REGISTERS, alignment=no padding, took
0.167 ms]
[removing optimized code for: dart.TreeIterator.moveNext$0]
The profile produced by --prof shows that slow.js is spending a lot of time
in Builtin_ArrayPush:
[C++ entry points]:
ticks cpp total name
1317 96.1% 64.7% v8::internal::Builtin_ArrayPush(int,
v8::internal::Object**, v8::internal::Isolate*)
16 1.2% 0.8% v8::internal::Runtime_DateCurrentTime(int,
v8::internal::Object**, v8::internal::Isolate*)
13 0.9% 0.6% v8::internal::Runtime_CompileLazy(int,
v8::internal::Object**, v8::internal::Isolate*)
9 0.7% 0.4% v8::internal::Runtime_CompileOptimized(int,
v8::internal::Object**, v8::internal::Isolate*)
5 0.4% 0.2% v8::internal::Runtime_LoadIC_Miss(int,
v8::internal::Object**, v8::internal::Isolate*)
presumably because it does not generate inlined code for the array push
builtin.
Attachments:
fast.js 76.2 KB
slow.js 76.2 KB
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