Proposal: Improved error message of "Error in array index"
simonmar at microsoft.com
Wed Nov 9 08:35:20 EST 2005
On 09 November 2005 11:52, Olaf Chitil wrote:
> Simon Marlow wrote:
>> I can explain why it happens,
>> though. The compiler has lifted out the error case into a top-level
>> x = error "Error in array index"
> So cost-centre stacks are not produced for the original program
> written by the user, but for the intermediate program after
> optimisation. I understand that you want to profile the optimised
> version, but the fact that your profile does not quite match your
> program can be confusing. For debugging, however, I think that it is
> clear that you want your debugging information (cost centre stacks)
> to match your program, even if it costs you some performance.
I completely agree! Indeed, the simplifier does try to maintain the
shape of the call graph when it transforms the program (perhaps not
The issue here I think is that we should treat exceptions in a similar
way to functions: when a function is called, the cost-centre stack of
the function is appended to the cost-centre stack of the call site, this
is how the call graph is built up. A thunk which evaluates to an
exception should probably behave in the same way, which would fix the
problem above (I'm not sure how easy this is to do, though).
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