Bug 125528

Summary: [MIPS] Redundant instructions in code generated from offlineasm.
Product: WebKit Reporter: Balazs Kilvady <kilvadyb>
Component: JavaScriptCoreAssignee: Nobody <webkit-unassigned>
Status: RESOLVED FIXED    
Severity: Normal CC: commit-queue, fpizlo, fu, gergely, ggaren, jbriance, msaboff, palfia
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: Unspecified   
OS: Unspecified   
Bug Depends on:    
Bug Blocks: 108664    
Attachments:
Description Flags
proposed patch. none

Balazs Kilvady
Reported 2013-12-10 11:57:31 PST
loadi TagOffset[cfr, index, 8], tag load PayloadOffset[cfr, index, 8], payload sequences are quite common in LowLevelInterpreter32_64.asm. On MIPS we don't have shifted addressing mode so when the lowering of the addresses goes independently by instructions then the generated code will be: sll $t8, $t2, 3 addu $t8, $t8, $fp lw $v1, 4($t8) sll $t8, $t2, 3 addu $t8, $t8, $fp lw $v0, 0($t8) The second sll; addu instructions are redundant.
Attachments
proposed patch. (5.43 KB, patch)
2013-12-10 12:27 PST, Balazs Kilvady 		no flags
DetailsFormatted DiffDiff
View All Add attachment proposed patch, testcase, etc.
Balazs Kilvady
Comment 1 2013-12-10 12:27:54 PST
Created attachment 218890 [details] proposed patch. This patch modifies the lowering of BaseIndex addresses to check instructions in pairs so it can leave out redundant MIPS code. Redundant MIPS instructions optimized out at 210 times processing the current LowLevelInterpreter.asm. It is hard to measure the speed of LLInt but performance test shows a small improvement: v8-v6: 19001.8ms -> 18855.0ms SunSpider: 5323.5ms -> 5316.1ms And at least the size of the code is smaller.
WebKit Commit Bot
Comment 2 2013-12-10 13:48:34 PST
Comment on attachment 218890 [details] proposed patch. Clearing flags on attachment: 218890 Committed r160387: <http://trac.webkit.org/changeset/160387>
WebKit Commit Bot
Comment 3 2013-12-10 13:48:36 PST
All reviewed patches have been landed. Closing bug.
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