[llvm] [LoopInterchange] Improve profitability check for vectorization (PR #133672)

[Ryotaro Kasuga via llvm-commits]

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@@ -221,13 +250,28 @@ static bool populateDependencyMatrix(CharMatrix &DepMatrix, unsigned Level,
           Dep.push_back('I');
         }
 
+        auto [Ite, Inserted] = Seen.try_emplace(
+            StringRef(Dep.data(), Dep.size()), DepMatrix.size());
+
         // Make sure we only add unique entries to the dependency matrix.
-        if (Seen.insert(StringRef(Dep.data(), Dep.size())).second)
+        if (Inserted) {
           DepMatrix.push_back(Dep);
+          IsForwardFlags.push_back(true);
+        }
+        if (!IsForward)
+          IsForwardFlags.reset(Ite->second);
       }
     }
   }
 
+  assert(DepMatrix.size() == IsForwardFlags.size() &&
+         "Dependency matrix and IsForwardVec should have the same size.");
+
+  // If all dependencies corresponding to a direction vector are forward, encode
+  // it to '<', otherwise to '*'.
+  for (unsigned I = 0; I != DepMatrix.size(); I++)
+    DepMatrix[I].push_back(IsForwardFlags[I] ? '<' : '*');
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kasuga-fj wrote:

> You could go as for as to encode it as `<` and `*` in another trailing element of the dependence vector.

Do you mean something like this?

https://github.com/llvm/llvm-project/pull/133672