[mlir][affine] Modify assertion into a user visible diagnostic

Author: Prakhar-Dixit

mlir/lib/Dialect/Vector/Utils/VectorUtils.cpp

@@ -141,8 +141,14 @@ static AffineMap makePermutationMap(
     unsigned countInvariantIndices = 0;
     for (unsigned dim = 0; dim < numIndices; ++dim) {
       if (!invariants.count(indices[dim])) {
-        assert(perm[kvp.second] == getAffineConstantExpr(0, context) &&
-               "permutationMap already has an entry along dim");
+        if (perm[kvp.second] != getAffineConstantExpr(0, context)) {
+          auto loopOp = cast<affine::AffineForOp>(kvp.first);
+          loopOp->emitError(
+              "loop induction variable is used in multiple indices, which is "
+              "unsupported for vectorization. Consider using nested loops "
+              "instead of a single loop with affine.apply.");
+          return AffineMap();
+        }
         perm[kvp.second] = getAffineDimExpr(dim, context);
       } else {
         ++countInvariantIndices;

mlir/test/Dialect/Affine/SuperVectorize/vectorize_unsupported.mlir

@@ -9,3 +9,38 @@ func.func @unparallel_loop_reduction_unsupported(%in: memref<256x512xf32>, %out:
  }
  return
 }
+
+// -----
+
+#map = affine_map<(d0)[s0] -> (d0 mod s0)>
+#map1 = affine_map<(d0)[s0] -> (d0 floordiv s0)>
+
+func.func @single_loop_unrolling_2D_access_pattern(%arg0: index) -> memref<2x2xf32> {
+  %c2 = arith.constant 2 : index
+  %cst = arith.constant 1.0 : f32
+  %alloc = memref.alloc() : memref<2x2xf32>
+    
+    affine.for %i = 0 to 4 {
+      %row = affine.apply #map1(%i)[%c2]  
+      %col = affine.apply #map(%i)[%c2]  
+      affine.store %cst, %alloc[%row, %col] : memref<2x2xf32>
+    }
+    
+    return %alloc : memref<2x2xf32>
+  }
+
+// CHECK: #[[$ATTR_0:.+]] = affine_map<(d0)[s0] -> (d0 floordiv s0)>
+// CHECK: #[[$ATTR_1:.+]] = affine_map<(d0)[s0] -> (d0 mod s0)>
+
+// CHECK-LABEL:   func.func @single_loop_unrolling_2D_access_pattern(
+// CHECK-SAME:                            %[[VAL_0:[0-9]+|[a-zA-Z$._-][a-zA-Z0-9$._-]*]]: index) -> memref<2x2xf32> {
+// CHECK:           %[[VAL_1:.*]] = arith.constant 2 : index
+// CHECK:           %[[VAL_2:.*]] = arith.constant 1.000000e+00 : f32
+// CHECK:           %[[VAL_3:.*]] = memref.alloc() : memref<2x2xf32>
+// CHECK:           affine.for %[[VAL_4:.*]] = 0 to 4 {
+// CHECK:             %[[VAL_5:.*]] = affine.apply #[[$ATTR_0]](%[[VAL_4]]){{\[}}%[[VAL_1]]]
+// CHECK:             %[[VAL_6:.*]] = affine.apply #[[$ATTR_1]](%[[VAL_4]]){{\[}}%[[VAL_1]]]
+// CHECK:             affine.store %[[VAL_2]], %[[VAL_3]]{{\[}}%[[VAL_5]], %[[VAL_6]]] : memref<2x2xf32>
+// CHECK:           }
+// CHECK:           return %[[VAL_3]] : memref<2x2xf32>
+// CHECK:         }