[PATCH] D73064: [LoopCacheAnalysis]: Add support for negative stride

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added a comment.

Correct me if I'm wrong but it seems you pretend negative steps are positive ones. While this is just a best-effort analysis, it seems wrong.
Take

  for (i = N; i > 0; i--)
    A[i] = A[N - i];

which should have a different cost than

  for (i = N; i > 0; i--)
    A[i] = A[i];

which is the same as

  for (i = 0; i < N; i++)
    A[i] = A[i];

Can you add these examples to the tests please?



================
Comment at: llvm/lib/Analysis/LoopCacheAnalysis.cpp:359
 
+      // The array may be accessed in reverse, for example:
+      //
----------------
The example code is not really helpful here.


================
Comment at: llvm/lib/Analysis/LoopCacheAnalysis.cpp:381
+                                    AccessFnAR->getNoWrapFlags());
+      }
       const SCEV *Div = SE.getUDivExactExpr(AccessFn, ElemSize);
----------------
No braces.


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