Bug 150761

Summary: Add conditional moves to the MacroAssembler
Product: WebKit Reporter: Filip Pizlo <fpizlo>
Component: JavaScriptCoreAssignee: Michael Saboff <msaboff>
Status: RESOLVED FIXED    
Severity: Normal CC: commit-queue, msaboff
Priority: P2    
Version: WebKit Nightly Build   
Hardware: All   
OS: All   
Bug Depends on:    
Bug Blocks: 150762    
Attachments:
Description Flags
Patch none

Filip Pizlo
Reported 2015-10-31 16:44:49 PDT
This would allow us to add Select to B3. The FTL uses Select quite a bit, so this is probably a good idea.
Attachments
Patch (9.61 KB, patch)
2015-11-03 18:02 PST, Michael Saboff 		no flags
DetailsFormatted DiffDiff
View All Add attachment proposed patch, testcase, etc.
Michael Saboff
Comment 1 2015-11-03 15:00:46 PST
Select is a non-branching instruction of the form x = select(a, b, c) where if a is non-zero then x = b else x = c. This is implemented using conditional moves, a CPU instruction that does not branch, but performs a move dependent on some condition. At the machine code level, a “cmov” is formatted very similarly to a branch, so it’s probably a matter of tweaking our branch formatting code. We probably want the API to be something like: m_jit.moveConditionally(LessThan, gpr1, gpr2, gpr3, gpr4); // move gpr3 to gpr4 if gpr1 is less than gpr2. m_jit.moveConditionallyTest(NonZero, gpr1, gpr2, gpr3, gpr4); // move gpr3 to gpr4 if (gpr1 & gpr2) != 0. m_jit.moveConditionallyDouble(DoubleEqual, fpr1, fpr2, gpr1, gpr2) // move gpr1 to gpr2 if fpr1 == fpr2.
Michael Saboff
Comment 2 2015-11-03 18:02:18 PST
Created attachment 264761 [details] Patch
WebKit Commit Bot
Comment 3 2015-11-07 10:11:36 PST
Comment on attachment 264761 [details] Patch Clearing flags on attachment: 264761 Committed r192131: <http://trac.webkit.org/changeset/192131>
WebKit Commit Bot
Comment 4 2015-11-07 10:11:40 PST
All reviewed patches have been landed. Closing bug.
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