[PATCH] D24918: [ADCE] Add code to remove dead branches

[Daniel Berlin via llvm-commits]

On Sat, Oct 1, 2016 at 9:25 AM, Mehdi Amini <mehdi.amini at apple.com> wrote:

>
> On Oct 1, 2016, at 9:22 AM, Daniel Berlin <dberlin at dberlin.org> wrote:
>
>
>
> On Sat, Oct 1, 2016, 9:36 AM David Callahan <dcallahan at fb.com> wrote:
>
>> david2050 added inline comments.
>>
>>
>> > dberlin wrote in ADCE.cpp:217
>> > I don't think this does what you think.
>> > The order here is not actually guaranteed to be in any particular
>> order, AFAIK.
>> >
>> > It happens most things produce blocks in lexical order, but this is not
>> guaranteed (again, AFAIK)
>> >
>> > Thus, it's entirely possible you see a successor before a predecessor,
>> which you will incorrectly mark a a back edge.
>> > Please just use a standard DFS approach that is guaranteed correct.
>>
>> This seems super simple and conservative in the sense it will catch all
>> loops.
>
>
>
> No actually, it will operate completely inconsistently unless bitcode
> guarantees an order.
>
>
> Order of basic-blocks is guaranteed when round-tripping to bitcode (We
> really try to avoid relying on other *use-list* though).
>

Is it also guaranteed that no matter what order they are produced in by the
frontend, they are in the same order once read in?
Otherwise, this code has the same problem
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