removeReturns.h

/*
Copyright 2013-present Barefoot Networks, Inc.
 
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
 
    http://www.apache.org/licenses/LICENSE-2.0
 
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
 
#ifndef FRONTENDS_P4_REMOVERETURNS_H_
#define FRONTENDS_P4_REMOVERETURNS_H_
 
#include "frontends/common/resolveReferences/resolveReferences.h"
#include "frontends/p4/ternaryBool.h"
#include "frontends/p4/typeChecking/typeChecker.h"
#include "ir/ir.h"
 
namespace P4 {
using namespace literals;
 
class HasExits : public Inspector {
 public:
    bool hasExits;
    bool hasReturns;
    HasExits() : hasExits(false), hasReturns(false) { setName("HasExits"); }
 
    void postorder(const IR::ExitStatement *) override { hasExits = true; }
    void postorder(const IR::ReturnStatement *) override { hasReturns = true; }
};
 
class MoveToElseAfterBranch : public Modifier {
    /* This pass does not use (inherit from) ControlFlowVisitor, even though it is doing
     * control flow analysis, as it turns out to be more efficient to do it directly here
     * by overloading the branching constructs (if/switch/loops) and not cloning the visitor,
     * because we *only* care about statements (not expressions) locally in a block (and
     * not across calls), and we only have one bit of data (hasJumped flag). */
 
    bool hasJumped = false;
 
    bool movedToIfBranch = false;
 
    bool preorder(IR::BlockStatement *) override;
    bool moveFromParentTo(const IR::Statement *&child);
    bool preorder(IR::IfStatement *) override;
    bool preorder(IR::SwitchStatement *) override;
    void postorder(IR::LoopStatement *) override;
    bool branch() {
        hasJumped = true;
        // no need to visit children
        return false;
    }
    bool preorder(IR::BreakStatement *) override { return branch(); }
    bool preorder(IR::ContinueStatement *) override { return branch(); }
    bool preorder(IR::ExitStatement *) override { return branch(); }
    bool preorder(IR::ReturnStatement *) override { return branch(); }
    // Only visit statements, skip all expressions
    bool preorder(IR::Expression *) override { return false; }
 
 public:
    MoveToElseAfterBranch() {}
};
 
class DoRemoveReturns : public Transform {
 protected:
    MinimalNameGenerator nameGen;
    IR::ID returnVar;      // one for each context
    IR::ID returnedValue;  // only for functions that return expressions
    cstring variableName;
    cstring retValName;
 
    std::vector<TernaryBool> stack;
    void push() { stack.push_back(TernaryBool::No); }
    void pop() { stack.pop_back(); }
    void set(TernaryBool r) {
        BUG_CHECK(!stack.empty(), "Empty stack");
        stack.back() = r;
    }
    TernaryBool hasReturned() {
        BUG_CHECK(!stack.empty(), "Empty stack");
        return stack.back();
    }
 
 public:
    explicit DoRemoveReturns(cstring varName = "hasReturned"_cs, cstring retValName = "retval"_cs)
        : variableName(varName), retValName(retValName) {
        visitDagOnce = false;
        setName("DoRemoveReturns");
    }
 
    const IR::Node *preorder(IR::Function *function) override;
    const IR::Node *preorder(IR::BlockStatement *statement) override;
    const IR::Node *preorder(IR::ReturnStatement *statement) override;
    const IR::Node *preorder(IR::ExitStatement *statement) override;
    const IR::Node *preorder(IR::IfStatement *statement) override;
    const IR::Node *preorder(IR::SwitchStatement *statement) override;
 
    const IR::Node *preorder(IR::P4Action *action) override;
    const IR::Node *preorder(IR::P4Control *control) override;
    const IR::Node *preorder(IR::P4Parser *parser) override {
        prune();
        return parser;
    }
 
    const IR::Node *postorder(IR::LoopStatement *loop) override;
    profile_t init_apply(const IR::Node *node) override;
};
 
class RemoveReturns : public PassManager {
 public:
    RemoveReturns() : PassManager({new MoveToElseAfterBranch(), new DoRemoveReturns()}) {}
};
 
}  // namespace P4
 
#endif /* FRONTENDS_P4_REMOVERETURNS_H_ */