Fix reduce_expr_modulo of vector in Solve.cpp (#8089)

* Fix reduce_expr_modulo of vector in Solve.cpp

* Fix test

Author: abadams

src/Solve.cpp

@@ -394,7 +394,7 @@ class SolveExpression : public IRMutator {
         if (a_uses_var && !b_uses_var) {
             const int64_t *ib = as_const_int(b);
             auto is_multiple_of_b = [&](const Expr &e) {
-                if (ib) {
+                if (ib && op->type.is_scalar()) {
                     int64_t r = 0;
                     return reduce_expr_modulo(e, *ib, &r) && r == 0;
                 } else {
@@ -1478,6 +1478,9 @@ void solve_test() {
     check_solve(min(x + y, x - z), x + min(y, 0 - z));
     check_solve(max(x + y, x - z), x + max(y, 0 - z));
 
+    check_solve((5 * Broadcast::make(x, 4) + y) / 5,
+                Broadcast::make(x, 4) + (Broadcast::make(y, 4) / 5));
+
     debug(0) << "Solve test passed\n";
 }