Comment #3 on issue 1506 by [email protected]: Optimization for
arguments.length
https://code.google.com/p/v8/issues/detail?id=1506
There is some improvement, but the compiler seems to think that the result
of arguments-length might not fit in a Smi, even though it is stored as a
Smi in the adaptor frame or would require a parameter list of several
gigabytes.
Perhaps it should have an InferRange.
--- Raw source ---
(a, b) {
"use strict";
return arguments.length;
}
--- Optimized code ---
optimization_id = 0
source_position = 13
kind = OPTIMIZED_FUNCTION
name = foo
stack_slots = 2
Instructions (size = 212)
0x4ac531e0 0 55 push ebp
0x4ac531e1 1 89e5 mov ebp,esp
0x4ac531e3 3 56 push esi
0x4ac531e4 4 57 push edi
0x4ac531e5 5 83ec08 sub esp,0x8
;;; Store dynamic frame alignment tag for spilled doubles
0x4ac531e8 8 c745f400000000 mov [ebp-0xc],0x0
;;; <@0,#0> -------------------- B0 --------------------
;;; <@2,#1> context
0x4ac531ef 15 8b45fc mov eax,[ebp-0x4]
;;; <@3,#1> gap
0x4ac531f2 18 8945f0 mov [ebp-0x10],eax
;;; <@12,#9> -------------------- B1 --------------------
;;; <@13,#9> gap
0x4ac531f5 21 89c6 mov esi,eax
;;; <@14,#11> stack-check
0x4ac531f7 23 3b25406c230b cmp esp,[0xb236c40]
0x4ac531fd 29 7305 jnc 36 (0x4ac53204)
0x4ac531ff 31 e8bcfffdff call StackCheck (0x4ac331c0) ;; code:
BUILTIN
;;; <@16,#11> lazy-bailout
;;; <@18,#13> arguments-elements
0x4ac53204 36 8b4500 mov eax,[ebp+0x0]
0x4ac53207 39 8b40fc mov eax,[eax-0x4]
0x4ac5320a 42 83f814 cmp eax,0x14
0x4ac5320d 45 7404 jz 51 (0x4ac53213)
0x4ac5320f 47 8bc5 mov eax,ebp
0x4ac53211 49 eb03 jmp 54 (0x4ac53216)
0x4ac53213 51 8b4500 mov eax,[ebp+0x0]
;;; <@20,#14> arguments-length
0x4ac53216 54 3be8 cmp ebp,eax
0x4ac53218 56 b902000000 mov ecx,0x2
0x4ac5321d 61 7408 jz 71 (0x4ac53227)
0x4ac5321f 63 8b4d00 mov ecx,[ebp+0x0]
0x4ac53222 66 8b49f4 mov ecx,[ecx-0xc]
0x4ac53225 69 d1f9 sar ecx,1
;;; <@22,#18> number-tag-i
0x4ac53227 71 03c9 add ecx,ecx
0x4ac53229 73 0f8008000000 jo 87 (0x4ac53237)
;;; <@23,#18> gap
0x4ac5322f 79 89c8 mov eax,ecx
;;; <@24,#16> return
0x4ac53231 81 89ec mov esp,ebp
0x4ac53233 83 5d pop ebp
0x4ac53234 84 c20c00 ret 0xc
;;; <@22,#18> -------------------- Deferred number-tag-i
--------------------
0x4ac53237 87 d1f9 sar ecx,1
0x4ac53239 89 81f100000080 xor ecx,0x80000000
0x4ac5323f 95 0f57c0 xorps xmm0,xmm0
0x4ac53242 98 f20f2ac1 cvtsi2sd xmm0,ecx
0x4ac53246 102 8b0d743c230b mov ecx,[0xb233c74]
0x4ac5324c 108 89c8 mov eax,ecx
0x4ac5324e 110 83c00c add eax,0xc
0x4ac53251 113 0f821c000000 jc 147 (0x4ac53273)
0x4ac53257 119 3b05783c230b cmp eax,[0xb233c78]
0x4ac5325d 125 0f8710000000 ja 147 (0x4ac53273)
0x4ac53263 131 8905743c230b mov [0xb233c74],eax
0x4ac53269 137 41 inc ecx
0x4ac5326a 138 c741ff7181b040 mov [ecx-0x1],0x40b08171 ;; object:
0x40b08171 <Map(elements=3)>
0x4ac53271 145 eb17 jmp 170 (0x4ac5328a)
0x4ac53273 147 33c9 xor ecx,ecx
0x4ac53275 149 60 pushad
0x4ac53276 150 8b75fc mov esi,[ebp-0x4]
0x4ac53279 153 33c0 xor eax,eax
0x4ac5327b 155 bb00df2d08 mov ebx,0x82ddf00
0x4ac53280 160 e8db6efbff call 0x4ac0a160 ;; code: STUB,
CEntryStub, minor: 1
0x4ac53285 165 89442418 mov [esp+0x18],eax
0x4ac53289 169 61 popad
0x4ac5328a 170 f20f114103 movsd [ecx+0x3],xmm0
0x4ac5328f 175 eb9e jmp 79 (0x4ac5322f)
0x4ac53291 177 90 nop
0x4ac53292 178 90 nop
0x4ac53293 179 90 nop
0x4ac53294 180 90 nop
0x4ac53295 181 90 nop
0x4ac53296 182 66 nop
0x4ac53297 183 90 nop
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