655810 - TI: Infinite loop and memory explosion with array2 test

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Alon Zakai (:azakai)]

Attachment: array2 test

The attached script is array2 from emscripten's test suite. With |-m -n| on JM, it enters an apparently infinite loop, and memory usage explodes out of control (be careful when running the script). Works ok with just -m.

Comment 1

[Jan de Mooij [:jandem]]

Can you still reproduce this? Works for me with 32-bit and 64-bit OS X shell, both |-m -n| and |-m -a -n|.

Comment 2

[Alon Zakai (:azakai)]

I still see this on Linux 32. Might be a platform specific thing then.

I get the same on most other emscripten tests as well (this is among the first in the list, so I saw it first).

Comment 3

[Jan de Mooij [:jandem]]

Ah this is interesting, debug build works on Linux 32-bit, but I can reproduce with a release build. Linux 32-bit tinderbox has the same problem, orange caused by time-outs. I'll reduce this now.

Comment 4

[Jan de Mooij [:jandem]]

Attachment: Patch

There are different versions of JS_FLOOR_LOG2 macro, apparently the optimized version returned an invalid value if the result is signed. The register was not in freeMask, causing an infinite loop in FrameState::merge (it was busy generating code, causing the memory explosion).

Comment 5

[Brian Hackett [Laid off!]]

Comment on attachment 531766 [details] [diff] [review]
Patch

Weird, any other hits on this?  possible to put a comment on the macro?

Comment 6

[Jan de Mooij [:jandem]]

I think the fix is correct, but it looks like JS_FLOOR_LOG2 is a red herring. The problem seems to be somewhere outside peekReg. Probably a bug in GCC 4.5 with -O3, I'll look closer tomorrow.

Comment 7

[Jan de Mooij [:jandem]]

Attachment: Patch

The (RegisterID)ireg cast was confusing GCC when ireg is a FP register. So maybe it's not a GCC bug but undefined behavior. We don't even need the int -> unsigned change but I left it in, it seems to be the right type.

There's another (RegisterID) cast in FrameState.cpp, but it's valid because RegisterID ranges from 0 to TotalRegisters.

Comment 8

[Jan de Mooij [:jandem]]

http://hg.mozilla.org/projects/jaegermonkey/rev/3f089c0d63f8