[llvm] [LV]Fix/improve max safe distance analysis (PR #121156)

[Alexey Bataev via llvm-commits]

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@@ -226,7 +226,7 @@ for.end:
 
 ;Check the new calculation of the maximum safe distance in bits which can be vectorized.
 ;The previous behavior did not take account that the stride was 2.
-;Therefore the maxVF was computed as 8 instead of 4, as the dependence distance here is 6 iterations, given by |N-(N-12)|/2.
+;Therefore the maxVF was computed as 8 instead of 2, as the dependence distance here is 6 iterations, given by |N-(N-12)|/2.
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alexey-bataev wrote:

I think so. If the dep distance is 6, the maxVF should be 2, not 4 (4 still introduces ineffective overlapping on the second iteration)

https://github.com/llvm/llvm-project/pull/121156