Bug 127245

Summary: Enable LLVM TailDup
Product: WebKit Reporter: Filip Pizlo <fpizlo>
Component: JavaScriptCoreAssignee: Filip Pizlo <fpizlo>
Severity: Normal CC: atrick, barraclough, ggaren, mark.lam, mhahnenberg, mmirman, msaboff, nrotem, oliver, sam
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: All   
OS: All   
Bug Depends on:    
Bug Blocks: 132356    
Description Flags
jsc patch
ggaren: review+
llvm patch none

Description Filip Pizlo 2014-01-18 20:17:58 PST
Patch forthcoming.
Comment 1 Filip Pizlo 2014-01-18 20:20:08 PST
Created attachment 221578 [details]
jsc patch
Comment 2 Filip Pizlo 2014-01-18 20:21:15 PST
Created attachment 221579 [details]
llvm patch

This just reverts LLVM r138841, and then updates the code a bit to various internal API changes.
Comment 3 Geoffrey Garen 2014-01-18 22:33:14 PST
Comment on attachment 221578 [details]
jsc patch

Comment 4 Geoffrey Garen 2014-01-18 22:35:07 PST
Comment on attachment 221579 [details]
llvm patch

Seems like it would be best to get this into LLVM trunk first.
Comment 5 Filip Pizlo 2014-01-18 22:39:16 PST
(In reply to comment #4)
> (From update of attachment 221579 [details])
> Seems like it would be best to get this into LLVM trunk first.

Yeah - that's definitely a blocker.

At the time that they removed TailDup there seemed to be multiple good justifications for doing so:

- It de-SSAifies the IR in a weird non-canonical way.
- It has demonstrably bad heuristics for important things like switch.
- It was unused in LLVM.

So it may be a challenge to get it pushed back in.  I suspect that this optimization is only good for JS because JS is so weird.
Comment 6 Filip Pizlo 2016-02-15 16:27:41 PST
We wrote our own compiler, and it has taildup.

*** This bug has been marked as a duplicate of bug 150279 ***