[PATCH] D19886: Add ability to use DependenceAnalysis from LoopAccessAnalysis

[silviu.baranga@arm.com via llvm-commits]

sbaranga added inline comments.

================
Comment at: lib/Analysis/LoopAccessAnalysis.cpp:1194
@@ +1193,3 @@
+      DEBUG(dbgs() << "LAA: DA returned no dependence!\n");
+      return Dependence::NoDep;
+    }
----------------
DA is independent of the loop versioning. Therefore if we have NoDep here then the versioning performed by replaceSymbolicStrideSCEV/isStridedPtr wouldn't help. So by moving this above the replaceSymbolicStrideSCEV calls, we could reduce the number of run-time checks needed.


================
Comment at: lib/Analysis/LoopAccessAnalysis.cpp:1212
@@ +1211,3 @@
+        // (Src - Sink).
+        Dist = PSE.getSE()->getNegativeSCEV(Dist);
+      }
----------------
etherzhhb wrote:
> In order to address @sbaranga's comment, perhaps we can rewrite Dist with SCEVPredicateRewriter using the existing Predicate from PSE to incorporate the existing runtime checks.  
Yes, something like that can be used to keep the existing features of the LAA dependece analysis, but it wouldn't help if we wanted to refactor and replace this logic entirely with DependenceAnalysis.

What are we getting by using the Dep->getDistance? It might be better to just keep the old distance calculation (which should be equivalent and avoid additional SCEV rewritting).



http://reviews.llvm.org/D19886