zeek/src/script_opt/IDOptInfo.cc

// See the file "COPYING" in the main distribution directory for copyright.

#include "zeek/script_opt/IDOptInfo.h"

#include "zeek/Desc.h"
#include "zeek/Expr.h"
#include "zeek/Stmt.h"
#include "zeek/script_opt/StmtOptInfo.h"

namespace zeek::detail {

const char* trace_ID = nullptr;

IDDefRegion::IDDefRegion(const Stmt* s, bool maybe, int def) {
    start_stmt = s->GetOptInfo()->stmt_num;
    block_level = s->GetOptInfo()->block_level;

    Init(maybe, def);
}

IDDefRegion::IDDefRegion(int stmt_num, int level, bool maybe, int def) {
    start_stmt = stmt_num;
    block_level = level;

    Init(maybe, def);
}

IDDefRegion::IDDefRegion(const Stmt* s, const IDDefRegion& ur) {
    start_stmt = s->GetOptInfo()->stmt_num;
    block_level = s->GetOptInfo()->block_level;

    Init(ur.MaybeDefined(), ur.DefinedAfter());
    SetDefExpr(ur.DefExprAfter());
}

void IDDefRegion::Dump() const {
    printf("\t%d->%d (%d): ", start_stmt, end_stmt, block_level);

    if ( defined != NO_DEF )
        printf("%d (%s)", defined, def_expr ? obj_desc(def_expr.get()).c_str() : "<no expr>");
    else if ( maybe_defined )
        printf("?");
    else
        printf("N/A");

    printf("\n");
}

std::vector<IDInitInfo> IDOptInfo::global_init_exprs;

void IDOptInfo::Clear() {
    static bool did_init = false;

    if ( ! did_init ) {
        trace_ID = getenv("ZEEK_TRACE_ID");
        did_init = true;
    }

    init_exprs.clear();
    usage_regions.clear();
    pending_confluences.clear();
    confluence_stmts.clear();

    tracing = trace_ID && util::streq(trace_ID, my_id->Name());
}

void IDOptInfo::AddInitExpr(ExprPtr init_expr, InitClass ic) {
    if ( ! init_expr )
        return;

    if ( my_id->IsGlobal() )
        global_init_exprs.emplace_back(my_id, init_expr, ic);

    init_exprs.emplace_back(std::move(init_expr));
}

void IDOptInfo::SetDefinedAfter(const Stmt* s, const ExprPtr& e, const std::vector<const Stmt*>& conf_blocks,
                                zeek_uint_t conf_start) {
    if ( tracing )
        printf("ID %s defined at %d: %s\n", trace_ID, s ? s->GetOptInfo()->stmt_num : NO_DEF,
               s ? obj_desc(s).c_str() : "<entry>");

    if ( ! s ) { // This is a definition-upon-entry
        ASSERT(usage_regions.empty());
        usage_regions.emplace_back(0, 0, true, 0);
        if ( tracing )
            DumpBlocks();
        return;
    }

    auto s_oi = s->GetOptInfo();
    auto stmt_num = s_oi->stmt_num;

    if ( usage_regions.empty() ) {
        // We're seeing this identifier for the first time,
        // so we don't have any context or confluence
        // information for it.  Create its "backstory" region.
        ASSERT(confluence_stmts.empty());
        usage_regions.emplace_back(0, 0, false, NO_DEF);
    }

    // Any pending regions stop prior to this statement.
    EndRegionsAfter(stmt_num - 1, s_oi->block_level);

    // Fill in any missing confluence blocks.
    int b = 0; // index into our own blocks
    int n = confluence_stmts.size();

    while ( b < n && conf_start < conf_blocks.size() ) {
        auto outer_block = conf_blocks[conf_start];

        // See if we can find that block.
        for ( ; b < n; ++b )
            if ( confluence_stmts[b] == outer_block )
                break;

        if ( b < n ) { // We found it, look for the next one.
            ++conf_start;
            ++b;
        }
    }

    // Add in the remainder.
    for ( ; conf_start < conf_blocks.size(); ++conf_start )
        StartConfluenceBlock(conf_blocks[conf_start]);

    if ( e ) {
        // If we just ended a region that's (1) at the same block level,
        // (2) definitive in terms of having assigned to the identifier,
        // and (3) adjacent to the one we're about to start (no intervening
        // confluence), then mark it as ended-due-to-assignment (as opposed
        // to ended-due-to-confluence). Doing so enables us to propagate that
        // assignment value to the beginning of this block in
        // FindRegionBeforeIndex() so we can collapse assignment cascades;
        // see the comment in that method.
        auto& ub = usage_regions.back();
        if ( ub.BlockLevel() == s->GetOptInfo()->block_level && ub.EndsAfter() == stmt_num - 1 && ub.DefExprAfter() )
            ub.SetEndedDueToAssignment();
    }

    // Create a new region corresponding to this definition.
    // This needs to come after filling out the confluence
    // blocks, since they'll create their own (earlier) regions.
    usage_regions.emplace_back(s, true, stmt_num);
    usage_regions.back().SetDefExpr(std::move(e));

    if ( tracing )
        DumpBlocks();
}

void IDOptInfo::ReturnAt(const Stmt* s) {
    if ( tracing )
        printf("ID %s subject to return %d: %s\n", trace_ID, s->GetOptInfo()->stmt_num, obj_desc(s).c_str());

    // Look for a catch-return that this would branch to.
    for ( int i = confluence_stmts.size() - 1; i >= 0; --i )
        if ( confluence_stmts[i]->Tag() == STMT_CATCH_RETURN ) {
            BranchBeyond(s, confluence_stmts[i], false);
            if ( tracing )
                DumpBlocks();
            return;
        }

    auto s_oi = s->GetOptInfo();
    EndRegionsAfter(s_oi->stmt_num - 1, s_oi->block_level);

    if ( tracing )
        DumpBlocks();
}

void IDOptInfo::BranchBackTo(const Stmt* from, const Stmt* to, bool close_all) {
    if ( tracing )
        printf("ID %s branching back from %d->%d: %s\n", trace_ID, from->GetOptInfo()->stmt_num,
               to->GetOptInfo()->stmt_num, obj_desc(from).c_str());

    // The key notion we need to update is whether the regions
    // between from_reg and to_reg still have unique definitions.
    // Confluence due to the branch can only take that away, it
    // can't instill it.  (OTOH, in principle it could update
    // "maybe defined", but not in a way we care about, since we
    // only draw upon that for diagnosing usage errors, and for
    // those the error has already occurred on entry into the loop.)

    auto from_reg = ActiveRegion();
    auto f_oi = from->GetOptInfo();
    auto t_oi = to->GetOptInfo();
    zeek_uint_t t_r_ind = FindRegionBeforeIndex(t_oi->stmt_num);
    auto& t_r = usage_regions[t_r_ind];

    if ( from_reg && from_reg->DefinedAfter() != t_r.DefinedAfter() && t_r.DefinedAfter() != NO_DEF ) {
        // They disagree on the definition.  Move the definition
        // point to be the start of the confluence region, and
        // update any blocks inside the region that refer to
        // a pre-"to" definition to instead reflect the confluence
        // region (and remove their definition expressions).
        int new_def = t_oi->stmt_num;

        for ( auto i = t_r_ind; i < usage_regions.size(); ++i ) {
            auto& ur = usage_regions[i];

            if ( ur.DefinedAfter() < new_def ) {
                ur.UpdateDefinedAfter(new_def);
                ur.SetDefExpr(nullptr);
            }
        }
    }

    int level = close_all ? t_oi->block_level + 1 : f_oi->block_level;
    EndRegionsAfter(f_oi->stmt_num, level);

    if ( tracing )
        DumpBlocks();
}

void IDOptInfo::BranchBeyond(const Stmt* end_s, const Stmt* block, bool close_all) {
    if ( tracing )
        printf("ID %s branching forward from %d beyond %d: %s\n", trace_ID, end_s->GetOptInfo()->stmt_num,
               block->GetOptInfo()->stmt_num, obj_desc(end_s).c_str());

    ASSERT(pending_confluences.count(block) > 0);

    auto ar = ActiveRegionIndex();
    if ( ar != NO_DEF )
        pending_confluences[block].insert(ar);

    auto end_oi = end_s->GetOptInfo();
    int level;
    if ( close_all )
        level = block->GetOptInfo()->block_level + 1;
    else
        level = end_oi->block_level;

    EndRegionsAfter(end_oi->stmt_num, level);

    if ( tracing )
        DumpBlocks();
}

void IDOptInfo::StartConfluenceBlock(const Stmt* s) {
    if ( tracing )
        printf("ID %s starting confluence block at %d: %s\n", trace_ID, s->GetOptInfo()->stmt_num, obj_desc(s).c_str());

    auto s_oi = s->GetOptInfo();
    int block_level = s_oi->block_level;

    // End any confluence blocks at this or inner levels.
    for ( auto cs : confluence_stmts ) {
        ASSERT(cs != s);

        auto cs_level = cs->GetOptInfo()->block_level;

        if ( cs_level >= block_level ) {
            ASSERT(cs_level == block_level);
            ASSERT(cs == confluence_stmts.back());
            EndRegionsAfter(s_oi->stmt_num - 1, block_level);
        }
    }

    pending_confluences[s] = {};
    confluence_stmts.push_back(s);
    block_has_orig_flow.push_back(s_oi->contains_branch_beyond);

    // Inherit the closest open, outer region, if necessary.
    for ( int i = usage_regions.size() - 1; i >= 0; --i ) {
        auto& ur = usage_regions[i];

        if ( ur.EndsAfter() == NO_DEF ) {
            if ( ur.BlockLevel() > block_level ) {
                // This can happen for regions left over
                // from a previous catch-return, which
                // we haven't closed out yet because we
                // don't track new identifiers beyond
                // outer CRs.  Close the region now.
                ASSERT(s->Tag() == STMT_CATCH_RETURN);
                ur.SetEndsAfter(s_oi->stmt_num - 1);
                continue;
            }

            if ( ur.BlockLevel() < block_level )
                // Didn't find one at our own level,
                // so create one inherited from the
                // outer one.
                usage_regions.emplace_back(s, ur);

            // We now have one at our level that we can use.
            break;
        }
    }

    if ( tracing )
        DumpBlocks();
}

void IDOptInfo::ConfluenceBlockEndsAfter(const Stmt* s, bool no_orig_flow) {
    auto stmt_num = s->GetOptInfo()->stmt_num;

    ASSERT(! confluence_stmts.empty());
    auto cs = confluence_stmts.back();
    auto& pc = pending_confluences[cs];

    // End any active regions.  Those will all have a level >= that
    // of cs, since we're now returning to cs's level.
    int cs_stmt_num = cs->GetOptInfo()->stmt_num;
    int cs_level = cs->GetOptInfo()->block_level;

    if ( tracing )
        printf("ID %s ending (%d) confluence block (%d, level %d) at %d: %s\n", trace_ID, no_orig_flow, cs_stmt_num,
               cs_level, stmt_num, obj_desc(s).c_str());

    if ( block_has_orig_flow.back() )
        no_orig_flow = false;

    // Compute the state of the definition at the point of confluence:
    // whether it's at least could-be-defined, whether it's definitely
    // defined and if so whether it has a single point of definition.
    bool maybe = false;
    bool defined = true;

    bool did_single_def = false;
    int single_def = NO_DEF;
    ExprPtr single_def_expr;
    bool have_multi_defs = false;

    int num_regions = 0;

    for ( auto i = 0U; i < usage_regions.size(); ++i ) {
        auto& ur = usage_regions[i];

        if ( ur.BlockLevel() < cs_level )
            // Region is not applicable.
            continue;

        if ( ur.EndsAfter() == NO_DEF ) { // End this region.
            ur.SetEndsAfter(stmt_num);

            if ( ur.StartsAfter() <= cs_stmt_num && no_orig_flow && pc.count(i) == 0 )
                // Don't include this region in our assessment.
                continue;
        }

        else if ( ur.EndsAfter() < cs_stmt_num )
            // Irrelevant, didn't extend into confluence region.
            // We test here just to avoid the set lookup in
            // the next test, which presumably will sometimes
            // be a tad expensive.
            continue;

        else if ( pc.count(i) == 0 )
            // This region isn't active, and we're not
            // tracking it for confluence.
            continue;

        ++num_regions;

        maybe = maybe || ur.MaybeDefined();

        if ( ur.DefinedAfter() == NO_DEF ) {
            defined = false;
            continue;
        }

        if ( did_single_def ) {
            if ( single_def != ur.DefinedAfter() )
                have_multi_defs = true;
        }
        else {
            single_def = ur.DefinedAfter();
            single_def_expr = ur.DefExprAfter();
            did_single_def = true;
        }
    }

    if ( num_regions == 0 ) { // Nothing survives.
        ASSERT(maybe == false);
        defined = false;
    }

    if ( ! defined ) {
        single_def = NO_DEF;
        have_multi_defs = false;
    }

    if ( have_multi_defs )
        // Definition reflects confluence point, which comes
        // just after 's'.
        single_def = stmt_num + 1;

    int level = cs->GetOptInfo()->block_level;
    usage_regions.emplace_back(stmt_num, level, maybe, single_def);

    if ( single_def != NO_DEF && ! have_multi_defs )
        usage_regions.back().SetDefExpr(single_def_expr);

    confluence_stmts.pop_back();
    block_has_orig_flow.pop_back();
    pending_confluences.erase(cs);

    if ( tracing )
        DumpBlocks();
}

bool IDOptInfo::IsPossiblyDefinedBefore(const Stmt* s) { return IsPossiblyDefinedBefore(s->GetOptInfo()->stmt_num); }

bool IDOptInfo::IsDefinedBefore(const Stmt* s) { return IsDefinedBefore(s->GetOptInfo()->stmt_num); }

int IDOptInfo::DefinitionBefore(const Stmt* s) { return DefinitionBefore(s->GetOptInfo()->stmt_num); }

ExprPtr IDOptInfo::DefExprBefore(const Stmt* s) { return DefExprBefore(s->GetOptInfo()->stmt_num); }

bool IDOptInfo::IsPossiblyDefinedBefore(int stmt_num) {
    if ( usage_regions.empty() )
        return false;

    return FindRegionBefore(stmt_num).MaybeDefined();
}

bool IDOptInfo::IsDefinedBefore(int stmt_num) {
    if ( usage_regions.empty() )
        return false;

    return FindRegionBefore(stmt_num).DefinedAfter() != NO_DEF;
}

int IDOptInfo::DefinitionBefore(int stmt_num) {
    if ( usage_regions.empty() )
        return NO_DEF;

    return FindRegionBefore(stmt_num).DefinedAfter();
}

ExprPtr IDOptInfo::DefExprBefore(int stmt_num) {
    if ( usage_regions.empty() )
        return nullptr;

    return FindRegionBefore(stmt_num).DefExprAfter();
}

void IDOptInfo::EndRegionsAfter(int stmt_num, int level) {
    for ( int i = usage_regions.size() - 1; i >= 0; --i ) {
        auto& ur = usage_regions[i];

        if ( ur.BlockLevel() < level )
            return;

        if ( ur.EndsAfter() == NO_DEF )
            ur.SetEndsAfter(stmt_num);
    }
}

int IDOptInfo::FindRegionBeforeIndex(int stmt_num) {
    int region_ind = NO_DEF;
    for ( auto i = 0U; i < usage_regions.size(); ++i ) {
        auto& ur = usage_regions[i];

        if ( ur.StartsAfter() >= stmt_num )
            break;

        // It's active for everything beyond its start.
        // or
        // It's active at the beginning of the statement of interest.
        if ( ur.EndsAfter() == NO_DEF || ur.EndsAfter() >= stmt_num )
            region_ind = i;

        else if ( ur.EndsAfter() == stmt_num - 1 && ur.EndedDueToAssignment() ) {
            // There's one other possibility, which occurs for a series of
            // statements like:
            //
            //	a = some_val;
            //	a = a + 1;
            //
            // Here, the assignment for "a = some_val" ends right after
            // that statement due to new assignment to 'a' on the second line.
            // However, it's okay to use the first region on the RHS.
            region_ind = i;
        }
    }

    ASSERT(region_ind != NO_DEF);
    return region_ind;
}

int IDOptInfo::ActiveRegionIndex() {
    int i;
    for ( i = usage_regions.size() - 1; i >= 0; --i )
        if ( usage_regions[i].EndsAfter() == NO_DEF )
            return i;

    return NO_DEF;
}

void IDOptInfo::DumpBlocks() const {
    for ( auto& ur : usage_regions )
        ur.Dump();

    printf("<end>\n");
}

} // namespace zeek::detail