[LoopInterchange] Fix the vectorizable check for a loop

llvm/lib/Transforms/Scalar/LoopInterchange.cpp

@@ -1197,25 +1197,35 @@ LoopInterchangeProfitability::isProfitablePerInstrOrderCost() {
   return std::nullopt;
 }
 
+/// Return true if we can vectorize the loop specified by \p LoopId.
+static bool canVectorize(const CharMatrix &DepMatrix, unsigned LoopId) {
+  for (unsigned I = 0; I != DepMatrix.size(); I++) {
+    char Dir = DepMatrix[I][LoopId];
+    if (Dir != 'I' && Dir != '=')
+      return false;
+  }
+  return true;
+}
+
 std::optional<bool> LoopInterchangeProfitability::isProfitableForVectorization(
     unsigned InnerLoopId, unsigned OuterLoopId, CharMatrix &DepMatrix) {
-  for (auto &Row : DepMatrix) {
-    // If the inner loop is loop independent or doesn't carry any dependency
-    // it is not profitable to move this to outer position, since we are
-    // likely able to do inner loop vectorization already.
-    if (Row[InnerLoopId] == 'I' || Row[InnerLoopId] == '=')
-      return std::optional<bool>(false);
-
-    // If the outer loop is not loop independent it is not profitable to move
-    // this to inner position, since doing so would not enable inner loop
-    // parallelism.
-    if (Row[OuterLoopId] != 'I' && Row[OuterLoopId] != '=')
-      return std::optional<bool>(false);
-  }
-  // If inner loop has dependence and outer loop is loop independent then it
-  // is/ profitable to interchange to enable inner loop parallelism.
-  // If there are no dependences, interchanging will not improve anything.
-  return std::optional<bool>(!DepMatrix.empty());
+  // If the outer loop is not loop independent it is not profitable to move
+  // this to inner position, since doing so would not enable inner loop
+  // parallelism.
+  if (!canVectorize(DepMatrix, OuterLoopId))
+    return false;
+
+  // If inner loop has dependence and outer loop is loop independent then it is
+  // profitable to interchange to enable inner loop parallelism.
+  if (!canVectorize(DepMatrix, InnerLoopId))
+    return true;
+
+  // If both the inner and the outer loop can be vectorized, it is necessary to
+  // check the cost of each vectorized loop for profitability decision. At this
+  // time we do not have a cost model to estimate them, so return nullopt.
+  // TODO: Estimate the cost of vectorized loop when both the outer and the
+  // inner loop can be vectorized.
+  return std::nullopt;
 }
 
 bool LoopInterchangeProfitability::isProfitable(

llvm/test/Transforms/LoopInterchange/profitability-vectorization-heuristic.ll

@@ -15,16 +15,13 @@
 ;   }
 ; }
 ;
-; FIXME: These loops are not exchanged at this time due to the problem in
-; profitability heuristic calculation for vectorization.
 
-; CHECK:      --- !Missed
+; CHECK:      --- !Passed
 ; CHECK-NEXT: Pass:            loop-interchange
-; CHECK-NEXT: Name:            InterchangeNotProfitable
+; CHECK-NEXT: Name:            Interchanged
 ; CHECK-NEXT: Function:        interchange_necessary_for_vectorization
 ; CHECK-NEXT: Args:
-; CHECK-NEXT:   - String:          Interchanging loops is not considered to improve cache locality nor vectorization.
-; CHECK-NEXT: ...
+; CHECK-NEXT:   - String:          Loop interchanged with enclosing loop.
 define void @interchange_necessary_for_vectorization() {
 entry:
   br label %for.i.header