[llvm-dev] SCEV cannot compute the trip count of Simple loop
Sanjoy Das via llvm-dev
llvm-dev at lists.llvm.org
Fri Sep 16 14:23:27 PDT 2016
Mehdi Amini wrote:
>> On Sep 16, 2016, at 1:56 PM, Kevin Choi via llvm-dev
>> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>> > int mat;
>> > for (p = (x+1) ; p < (x+3) ;p++)
>> > mat[x][p-1][i] = mat[x][p-1][i] + 5;____
>> > }
>> The trip count of 2 should be valid for x in [0,6].
> It is not clear to me why the trip count of 2 isn’t *always* valid.
It is always valid to return 2 as the trip count. But SCEV today is
not always able to exploit nsw/nuw due to some systemic issues.
I can go into details about the systemic issues here if you want, but
given that I've already repeated this several times on the mailing
list, I'd rather put that into a blog post to have a link to share
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