Bug 125425

Summary: Fold storage pointer for GC-allocated typed arrays
Product: WebKit Reporter: Filip Pizlo <fpizlo>
Component: JavaScriptCoreAssignee: Filip Pizlo <fpizlo>
Status: REOPENED ---    
Severity: Normal CC: barraclough, ggaren, mark.lam, mhahnenberg, msaboff, oliver, sam
Priority: P2    
Version: 528+ (Nightly build)   
Hardware: All   
OS: All   

Description Filip Pizlo 2013-12-08 12:04:26 PST 
This probably won't be *too* profitable but I suspect that eventually it'll be needed.
Comment 1 Filip Pizlo 2016-08-23 13:43:12 PDT 

*** This bug has been marked as a duplicate of bug 161100 ***
Comment 2 Filip Pizlo 2016-08-23 15:15:22 PDT 
Nope, this is still a bug.

Even if the GC-allocated typed array doesn't move, we still can't constant-fold pointers to it because of neutering:

- To constant-fold, we need to install a watchpoint on the typed array's underlying buffer to make sure that we get notified if it gets neutered.
- To install a watchpoint, we need to request the buffer.
- To request the buffer, we need to move the backing store out of GC space.
- To move it out of GC space, we need to malloc a new backing store and copy the data over and repoint m_vector.
- Therefore, constant folding will fold to the *old* buffer.

Ouch!