Comment author: administrator

Dear Markus,

I have just discovered that some program that used to work fine up to
(including) OCaml 3.07+2 doesn't work with the most recent CVS-snapshot
3.07+5 (2003-11-19). It suddenly raises the exception Out_of_memory for
no apparent reason.

The change in the CVS most likely to cause this behavior is a
modification in the polymorphic comparison operators (=, <, etc):
in order to correct their behavior w.r.t. float NaNs, they now perform
a full traversal of their arguments. This means that they will loop
or raise Out_of_memory when given cyclic arguments, while the old
implementation may loop or raise Out_of_memory, but could also stop
early on an == situation.

The backtrace yields the following:

Fatal error: exception Out_of_memory
Raised by primitive operation at file "format.ml", line 1000, character 4
Called from file "format.ml", line 1000, character 4
Called from file "format.ml", line 994, character 4
Called from file "list.ml", line 74, character 34
Called from file "format.ml", line 994, character 4
Called from file "list.ml", line 74, character 34
Called from file "format.ml", line 1000, character 4
Called from file "format.ml", line 1000, character 4
Called from file "sym_reg_gen.ml", line 11, character 35

The backtrace is a bit incomplete (and I'll have to understand why),
but could you please look at file "sym_reg_gen.ml" circa line 11 and
see whether there would be a call to a polymorphic comparison on a
potentially cyclic argument nearby?

If you can't find any, I'm willing to investigate the problem. No
need to shrink your example: just send me a complete repro case, no
matter how big.

Thanks for your testing,

• Xavier Leroy

Comment author: administrator

Polymorphic comparison applied to cyclic value. (Confirmed by Markus.)