[BugFix] Conditions Robustness in dynamic vectorize (#404)

src/transform/loop_vectorize_dynamic.cc

@@ -396,10 +396,13 @@ private:
     VectorizedConditionMutator condition_mutator(inner_var, vector_size_);
 
     // Adaptively set vectorized variable to the min/max value of the extent
-    PrimExpr condition_bound = condition_mutator(conditions[0]);
+    PrimExpr condition_bound;
+    if (conditions.size() > 0) {
+      condition_bound = condition_mutator(conditions[0]);
       for (int i = 1; i < conditions.size(); ++i) {
         condition_bound = condition_bound && condition_mutator(conditions[i]);
       }
+    }
 
     if (!disable_dynamic_tail_split) {
       // If dynamic_tail_split is true, we will vectorize the loop with
@@ -411,7 +414,11 @@ private:
       For vectorize_for =
           For(inner_var, 0, vector_size_, ForKind::kVectorized, vectorize_body);
       For serial_for = For(inner_var, 0, vector_size_, ForKind::kSerial, body);
+      if (conditions.size() > 0) {
         body = IfThenElse(condition_bound, vectorize_for, serial_for);
+      } else {
+        body = vectorize_for;
+      }
       body = For(outer_var, 0, extent / vector_size_, fnode->kind, body,
                  fnode->thread_binding, fnode->annotations, fnode->span);
       return body;