Consider *all* Exprs a func uses, not just the RHS, in Li2018 (#8326)

Fixes #8312

Author: abadams

src/DerivativeUtils.cpp

@@ -253,7 +253,7 @@ map<string, Box> inference_bounds(const vector<Func> &funcs,
     for (auto it = order.rbegin(); it != order.rend(); it++) {
         Func func = Func(env[*it]);
         // We should already have the bounds of this function
-        internal_assert(bounds.find(*it) != bounds.end());
+        internal_assert(bounds.find(*it) != bounds.end()) << *it << "\n";
         const Box &current_bounds = bounds[*it];
         internal_assert(func.args().size() == current_bounds.size());
         // We know the range for each argument of this function
@@ -262,29 +262,33 @@ map<string, Box> inference_bounds(const vector<Func> &funcs,
             scope.push(arg, current_bounds[i]);
         }
         // Propagate the bounds
-        for (int update_id = -1; update_id < func.num_update_definitions(); update_id++) {
-            // For each rhs expression
-            Tuple tuple = update_id == -1 ? func.values() : func.update_values(update_id);
-            for (const auto &expr : tuple.as_vector()) {
-                // For all the immediate dependencies of this expression,
-                // find the required ranges
-                map<string, Box> update_bounds =
-                    boxes_required(expr, scope, func_value_bounds);
-                // Loop over the dependencies
-                for (const auto &it : update_bounds) {
-                    if (it.first == func.name()) {
-                        // Skip self reference
-                        continue;
-                    }
-                    // Update the bounds, if not exists then create a new one
-                    auto found = bounds.find(it.first);
-                    if (found == bounds.end()) {
-                        bounds[it.first] = it.second;
-                    } else {
-                        Box new_box = box_union(found->second, it.second);
-                        bounds[it.first] = new_box;
-                    }
-                }
+        class CollectExprs : public IRMutator {
+        public:
+            using IRMutator::mutate;
+            Expr mutate(const Expr &e) override {
+                exprs.push_back(e);
+                return e;
+            }
+            std::vector<Expr> exprs;
+        } expr_collector;
+        func.function().mutate(&expr_collector);
+
+        Expr bundle = Call::make(Int(32), Call::bundle, expr_collector.exprs, Call::PureIntrinsic);
+        map<string, Box> update_bounds =
+            boxes_required(bundle, scope, func_value_bounds);
+        // Loop over the dependencies
+        for (const auto &it : update_bounds) {
+            if (it.first == func.name()) {
+                // Skip self reference
+                continue;
+            }
+            // Update the bounds, if not exists then create a new one
+            auto found = bounds.find(it.first);
+            if (found == bounds.end()) {
+                bounds[it.first] = it.second;
+            } else {
+                Box new_box = box_union(found->second, it.second);
+                bounds[it.first] = new_box;
             }
         }
         for (int i = 0; i < (int)current_bounds.size(); i++) {