Revert "Runtime: fix annotation of caml_compare"

[OlivierNicole]

This reverts commit 3ceafdf: caml_compare can raise Invalid_argument.

Fixes #2089.

[hhugo]

Maybe add a comment next to //Provides to explain why it's not "mutable"

[OlivierNicole]

Done. I’m still wondering why the annotation is “mutable”.

[hhugo]

Done. I’m still wondering why the annotation is “mutable”.

It means that the call cannot be reordered with a "mutator" call.

[OlivierNicole]

Isn’t it the opposite? mutable seems to mean that there are no side effects.

[vouillon]

We have three purity annotations:

• mutator (the default): the primitive may have side-effects
• mutable: the primitive does not have side-effects, but cannot be reordered with effectful operations (for instance, when one of the parameter is a mutable datastructure)
• pure: the primitive will always return the same value (given the same parameters).

[OlivierNicole]

I understand now, thanks!