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Re: Question about always executed info computed in tree-ssa-loop-im.c

On Wed, Jul 8, 2015 at 5:58 PM, Bin.Cheng <> wrote:
> On Wed, Jul 8, 2015 at 5:51 PM, Richard Biener
> <> wrote:
>> On Wed, Jul 8, 2015 at 8:52 AM, Bin.Cheng <> wrote:
>>> Hi,
>>> Function fill_always_executed_in_1 computes basic blocks' always
>>> executed information, and it has below code and comment:
>>>           /* In a loop that is always entered we may proceed anyway.
>>>          But record that we entered it and stop once we leave it.  */
>>>           inn_loop = bb->loop_father;
>>> Then in following iterations, it breaks the loop if basic block not
>>> belonging to the inner loop is encountered.  This means basic blocks
>>> after inner loop won't have always executed information computed, even
>>> they dominates the original loop's latch.
>>> Am I missing something?  Why is that?
>> To improve here it would need to verify that all exits of the inner loop
>> exit to the same BB of the outer loop and that no exit skips any blocks
>> in the outer loop.  Like for
> But we are working on dominating tree anyway.  Won't dominating latch be enough?
> Thanks,
> bin
>>   for (;;)
>>     {
>>       for (;;) { if (x) goto skip; if (y) break }
>>       foo();
>>     skip:
>>     }
>> so it is just a simple and conservative algorithm it seems.  It's also
>> quadratic in the number of BBs of the outermost loop.
What we need to do is check if inner loop's exit goes to basic block
not belonging to outer loop?


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