Bug 65095

Summary: X86-64 assembler emits three instructions instead of two for certain loads and stores
Product: WebKit Reporter: Filip Pizlo <fpizlo>
Component: JavaScriptCoreAssignee: Nobody <webkit-unassigned>
Status: RESOLVED FIXED    
Severity: Normal CC: barraclough, fpizlo, webkit.review.bot
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: All   
OS: All   
Attachments:
Description Flags
the patch none

Filip Pizlo
Reported 2011-07-24 22:54:16 PDT
The only X86-64 instructions for storing to, or loading from, 64-bit absolute immediate addresses require that the source of the store (or the target of the load) is EAX. If the X86-64 assembler in JSC is asked to emit code for storing, or loading, an absolute immediate address where the register containing the value is not EAX, it will emit two additional instructions to swap values between EAX and the requested register. This is not as efficient as simply moving the 64-bit address into the assembler's scratch register, which would result in two instructions.
Attachments
the patch (2.81 KB, patch)
2011-07-24 22:59 PDT, Filip Pizlo 		no flags
DetailsFormatted DiffDiff
View All Add attachment proposed patch, testcase, etc.
Filip Pizlo
Comment 1 2011-07-24 22:59:22 PDT
Created attachment 101850 [details] the patch
WebKit Review Bot
Comment 2 2011-07-25 10:59:21 PDT
Comment on attachment 101850 [details] the patch Clearing flags on attachment: 101850 Committed r91678: <http://trac.webkit.org/changeset/91678>
WebKit Review Bot
Comment 3 2011-07-25 10:59:25 PDT
All reviewed patches have been landed. Closing bug.
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