716119 - Miscompilation of conditional expressions

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jérôme Vouillon]

The Javascript code at http://www.pps.jussieu.fr/~vouillon/bug/ is not interpreted correctly by Firefox 9: it should display a nice graph, but instead displays ellipses all over the place.

I have tracked this down to what looks like the miscompilation of the conditional expression (pi_A9_<alpha_Hl_?1:0) on line 4881 in hypertree.js. Indeed, I have added the following debugging code:

    _wh_.log(start_Hk_,fin_Hl_,alpha_Hm_,pi_A9_<alpha_Hm_?1:0);

where _wh_ is window.console, _pi_A9_ = 3.1415...
(This is computer-generated code, and I made the change in the source code, so the variable names are not exactly the same.)
Then, I get incorrect outputs like the following one:

      -1.570796326794897 -1.2702070146247024 0.30058931217019413 1

Clearly, the last number should be 0.

I don't know how to reproduce the bug in a smaller program.  In particular, I seem to get correct outputs when I change slightly the line above, for instance by removing the first two arguments start_Hk_ and fin_Hl_, or by replacing _wh_ by window.console.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Turning off TI makes the problem go away...

I also see the problem in nightlies.

Comment 2

[Brian Hackett [Laid off!]]

Attachment: patch

Regalloc bug when doing a branch based on values known to be floating point numbers.  We didn't take care to ensure that sync code did not clobber the registers that were about to be compared, so the comparison could end up using incorrect values in the lhs/rhs.

I like the website, I've seen a fair number of those critters while diving here in california.

Comment 3

[Brian Hackett [Laid off!]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/2b2ca37b0305

Comment 4

[Marco Bonardo [:mak]]

https://hg.mozilla.org/mozilla-central/rev/2b2ca37b0305

Comment 5

[Alex Keybl [:akeybl]]

This is a regression in FF9, and we're not seeing any dupes, so I'm untracking for 11/12/13. This can ride the trains.