------- Additional Comments From sebastian dot pop at cri dot ensmp dot fr
2005-09-14 12:38 -------
Subject: Re: [data deps] Distance on outer loops for self output deps
In this case neither implementation got the dependece right: there are
bugs in both implementations. For the following nested loop:
loop_1
loop_2
A[5] = ...
end_loop_2
end_loop_1
BAD would answer: (1, 1), that would mean that for getting the same
access we'd have to run loop_1 once *and* loop_2 once: this is false.
BOP would answer: (0, 0), that would mean that neither loop_1 nor
loop_2 carry dependences, in other words, both loops are parallel:
this is false.
The right answer is a set of distance vectors: (0, 1) and (1, 0). For
getting to the same element in the array we have to run loop_1 once
*or* loop_2 has to run once.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23411
