724517 - IonMonkey: Folding null/undefined in jsop_getelem_dense is not safe

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jan de Mooij [:jandem]]

I modified ss-fannkuch to work around the missing JSOP_NOT support (bug 709240) and hit an assertion failure. While reducing this assert, I hit an (unrelated) inference failure.

The problem is that we can't fold null/undefined in jsop_getelem_dense, since the resulting SSA no longer mimics the bytecode (required by IsPhiObservable).

Comment 1

[Jan de Mooij [:jandem]]

Attachment: Fix + test

Also has a trivial fix for an unrelated STRICTEQ/NE assert I had in my queue - I don't think it deserves its own bug.

Comment 2

[David Anderson [:dvander] - inactive, e-mail if emergency]

Comment on attachment 594681 [details] [diff] [review]
Fix + test

Okay, I think I understand this now: the way EliminateDeadPhis works requires that we consider the uses in the bytecode to be uses in the SSA as well. If we eliminate the LoadElement of |perm| we consider |perm| as dead.

This is tricky and I wouldn't be surprised if we end up deciding to overhaul EliminateDeadPhis later.

Comment 3

[Jan de Mooij [:jandem]]

http://hg.mozilla.org/projects/ionmonkey/rev/a1fc5b03be76