action_synthesis_policy.h

 
#ifndef BF_P4C_MIDEND_ACTION_SYNTHESIS_POLICY_H_
#define BF_P4C_MIDEND_ACTION_SYNTHESIS_POLICY_H_
 
#include "backends/tofino/bf-p4c/ir/tofino_write_context.h"
#include "backends/tofino/bf-p4c/midend/register_read_write.h"
#include "midend/actionSynthesis.h"
 
namespace BFN {
 
class ActionSynthesisPolicy : public P4::ActionSynthesisPolicy {
    P4::ReferenceMap *refMap;
    P4::TypeMap *typeMap;
    // set of controls where actions are not synthesized
    const std::set<cstring> *skip;
 
    bool convert(const Visitor::Context *, const IR::P4Control *control) override {
        if (control->is<IR::BFN::TnaDeparser>()) {
            return false;
        }
        for (auto c : *skip)
            if (control->name == c) return false;
        return true;
    }
 
    static const IR::Type_Extern *externType(const IR::Type *type) {
        if (auto *spec = type->to<IR::Type_SpecializedCanonical>()) type = spec->baseType;
        return type->to<IR::Type_Extern>();
    }
 
    class FindPathsWritten : public Inspector, TofinoWriteContext {
        std::set<cstring> &writes;
        bool preorder(const IR::PathExpression *pe) {
            if (isWrite()) writes.insert(pe->toString());
            return false;
        }
        bool preorder(const IR::Member *m) {
            if (isWrite()) writes.insert(m->toString());
            return false;
        }
        bool preorder(const IR::AssignmentStatement *assign) {
            // special case -- ignore writing the result of a 'hash.get' call to a var,
            // as we can use that directly in the same action (hash is computed in ixbar hash)
            if (auto *mc = assign->right->to<IR::MethodCallExpression>()) {
                if (auto *m = mc->method->to<IR::Member>()) {
                    if (auto *et = externType(m->expr->type)) {
                        if (et->name == "Hash" && m->member == "get") return false;
                    }
                }
            }
            return true;
        }
 
     public:
        explicit FindPathsWritten(std::set<cstring> &w) : writes(w) {}
    };
 
    class DependsOnPaths : public Inspector {
        ActionSynthesisPolicy &self;
        std::set<cstring> &paths;
        bool rv = false;
        bool preorder(const IR::PathExpression *pe) {
            if (paths.count(pe->toString())) rv = true;
            return !rv;
        }
        bool preorder(const IR::Member *m) {
            if (paths.count(m->toString())) rv = true;
            return !rv;
        }
        bool preorder(const IR::Node *) { return !rv; }
        void postorder(const IR::MethodCallExpression *mc) {
            auto *mi = P4::MethodInstance::resolve(mc, self.refMap, self.typeMap, true);
            if (auto *em = mi ? mi->to<P4::ExternMethod>() : nullptr) {
                for (auto *n : em->mayCall()) {
                    if (auto *fn = n->to<IR::Function>()) {
                        visit(fn->body, "body");
                    }
                }
            }
        }
 
     public:
        explicit operator bool() { return rv; }
        DependsOnPaths(ActionSynthesisPolicy &self, const IR::Node *n, std::set<cstring> &p)
            : self(self), paths(p), rv(false) {
            n->apply(*this);
        }
    };
 
    class ReferencesExtern : public Inspector {
        bool rv = false;
        bool preorder(const IR::PathExpression *pe) {
            if (rv) return false;
            auto *et = externType(pe->type);
            if (et && et->name != "Hash") {
                rv = true;
            }
            return !rv;
        }
        bool preorder(const IR::Node *) { return !rv; }
 
     public:
        explicit operator bool() { return rv; }
        explicit ReferencesExtern(const IR::Node *n) { n->apply(*this); }
    };
 
    bool isRegisterWriteAfterRead(const IR::BlockStatement *blk, const IR::StatOrDecl *stmt_decl) {
        auto *blk_stmt = blk->components.back()->to<IR::Statement>();
        if (!blk_stmt) return false;
        auto read_rv = BFN::RegisterReadWrite::extractRegisterReadWrite(blk_stmt);
        auto *read_mce = read_rv.first;
        if (!read_mce) return false;
 
        auto *stmt = stmt_decl->to<IR::Statement>();
        if (!stmt) return false;
        auto write_rv = BFN::RegisterReadWrite::extractRegisterReadWrite(stmt);
        auto *write_mce = write_rv.first;
        if (!write_mce) return false;
 
        auto *read_inst = P4::MethodInstance::resolve(read_mce, refMap, typeMap);
        // Check also object becuase of plain functions
        if (!read_inst || !read_inst->object) return false;
        auto *read_decl = read_inst->object->to<IR::Declaration_Instance>();
        if (!read_decl) return false;
 
        auto *read_member = read_mce->method->to<IR::Member>();
        if (!read_member) return false;
        auto *read_extern_type = externType(read_member->expr->type);
        if (!read_extern_type) return false;
        if (read_extern_type->name != "Register" || read_member->member != "read") return false;
 
        auto *write_inst = P4::MethodInstance::resolve(write_mce, refMap, typeMap);
        // Check also object becuase of plain functions
        if (!write_inst || !write_inst->object) return false;
        auto *write_decl = write_inst->object->to<IR::Declaration_Instance>();
        if (!write_decl) return false;
 
        auto *write_member = write_mce->method->to<IR::Member>();
        if (!write_member) return false;
        auto *write_extern_type = externType(write_member->expr->type);
        if (!write_extern_type) return false;
        if (write_extern_type->name != "Register" || write_member->member != "write") return false;
 
        if (read_decl->declid != write_decl->declid) return false;
 
        return true;
    }
 
    bool can_combine(const Visitor::Context *, const IR::BlockStatement *blk,
                     const IR::StatOrDecl *stmt) override {
        if (isRegisterWriteAfterRead(blk, stmt)) return true;
        std::set<cstring> writes;
        if (ReferencesExtern(blk) && ReferencesExtern(stmt)) return false;
        blk->apply(FindPathsWritten(writes));
        return !DependsOnPaths(*this, stmt, writes);
    }
 
 public:
    ActionSynthesisPolicy(const std::set<cstring> *skip, P4::ReferenceMap *refMap,
                          P4::TypeMap *typeMap)
        : refMap(refMap), typeMap(typeMap), skip(skip) {
        CHECK_NULL(skip);
    }
};
 
}  // namespace BFN
 
#endif /* BF_P4C_MIDEND_ACTION_SYNTHESIS_POLICY_H_ */