>> let x = ... in
>> (* here you are not sure x is collected even if the variable does not
>> appear after this comment *)
>>   
>>     
> Thanks for making this clear. I was indeed thinking that collecting x 
> here could require some sort of variable liveness analysis, and that the
> GC might not be that smart, and this is why I tried to put x in a
> function and prevent inlining, but I don't know if it is enough to make
> x definitely unreachable.
>   
If your problem is still not solved, may be you should post your code or 
an example reproducing the problem.

Cheers,
Christophe