field_pov_analysis.h

 
#ifndef BACKENDS_TOFINO_BF_P4C_PARDE_CLOT_FIELD_POV_ANALYSIS_H_
#define BACKENDS_TOFINO_BF_P4C_PARDE_CLOT_FIELD_POV_ANALYSIS_H_
 
#include "backends/tofino/bf-p4c/parde/clot/clot_info.h"
#include "backends/tofino/bf-p4c/parde/parser_info.h"
 
/* This pass is a parser data flow analysis to find if a field is extracted from
 * the packet in every path that sets the field's valid bit. If there exists a path
 * where valid bit is set but no fields of the corresponding header is extracted
 * from the packet then such fields should not be placed in clots.
 *
 * The analysis proceeds in topological sorted order.
 * Every state has two bitvectors :
 *    1. field_vec : Contains fields that are definitely extracted from the packet before
 *                   the current state
 *    2. pov_vec : Valid bits that are set before the current state and are waiting for
                   corresponding fields to be extracted.
 *
 * The current state will add a field in its field_vec if any of these conditions are met:
 *    1. Field is extracted from the packet in the current state
 *    2. The field is present in all the immediate predecessors' field_vec
 *
 * Subsequently, the current state will add a valid bit in its pov_vec if
 * any of these conditions are met:
 *     1. The valid bit is set in current state and the field is not present in the
          field_vec of the current state
 *     2. Valid bit is set in any immediate predecessors' pov_vec and the field is not present
 *        in the field_vec for the current state.
 *
 * If the current state transitions to end, then the povbits that are set in pov_vec
 * are added in pov_extracted_without_fields.
 */
class FieldPovAnalysis : public Inspector {
    ClotInfo &clotInfo;
    const PhvInfo &phv;
    std::set<const IR::BFN::Parser *> parsers;
    std::map<const PHV::Field *, std::set<const PHV::Field *>> pov_to_fields;
 
    std::map<cstring, std::pair<bitvec, bitvec>> state_to_field_pov;
    bool preorder(const IR::BFN::Parser *parser) override;
    bool preorder(const IR::BFN::EmitField *emit) override;
    void end_apply() override;
 
 public:
    std::set<const PHV::Field *> pov_extracted_without_fields;
    FieldPovAnalysis(ClotInfo &clotInfo, const PhvInfo &phv) : clotInfo(clotInfo), phv(phv) {}
    Visitor::profile_t init_apply(const IR::Node *root) override {
        profile_t rv = Inspector::init_apply(root);
        pov_to_fields.clear();
        state_to_field_pov.clear();
        parsers.clear();
        return rv;
    }
};
 
#endif /* BACKENDS_TOFINO_BF_P4C_PARDE_CLOT_FIELD_POV_ANALYSIS_H_ */