[PATCH] D22630: Loop rotation

[Eli Friedman via llvm-commits]

On Thu, Jul 28, 2016 at 2:46 PM, Sanjoy Das via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> After rotating the inner loop, won't the program have to be
>
>    for (int i = 0; i < m; ++i) {
>     x = A->at(n * i);
>     if (exception)
>       throw;
>     y = B->at(n*i);
>     if(exception)
>       throw;
>     res += x + y;
>     for (int j = 1; j < n; ++j)  // << changed lower count
>       res += A->at(n * i + j) + B->at(n * i + j);
>    }
>
> Where is the redundancy here ^?
> <http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits>
>

If you look at the actual LLVM IR for the original C++ example, you'll see
that some of the checks can be simplified because we can assume B is
dereferencable.

-Eli
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