verilator/src/V3SplitAs.cpp

// -*- mode: C++; c-file-style: "cc-mode" -*-
//*************************************************************************
// DESCRIPTION: Verilator: Break always into separate statements to reduce temps
//
// Code available from: https://verilator.org
//
//*************************************************************************
//
// Copyright 2003-2020 by Wilson Snyder. This program is free software; you
// can redistribute it and/or modify it under the terms of either the GNU
// Lesser General Public License Version 3 or the Perl Artistic License
// Version 2.0.
// SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
//
//*************************************************************************
// V3SplitAs's Transformations:
//
//      Search each ALWAYS for a VARREF lvalue with a /*isolate_assignments*/ attribute
//      If found, color statements with both, assignment to that varref, or other assignments.
//      Replicate the Always, and remove mis-colored duplicate code.
//
//*************************************************************************

#include "config_build.h"
#include "verilatedos.h"

#include "V3Global.h"
#include "V3SplitAs.h"
#include "V3Stats.h"
#include "V3Ast.h"

#include <map>

//######################################################################

class SplitAsBaseVisitor : public AstNVisitor {
public:
    // METHODS
    VL_DEBUG_FUNC;  // Declare debug()
};

//######################################################################
// Find all split variables in a block

class SplitAsFindVisitor : public SplitAsBaseVisitor {
private:
    // STATE
    AstVarScope* m_splitVscp = nullptr;  // Variable we want to split

    // METHODS
    virtual void visit(AstVarRef* nodep) override {
        if (nodep->lvalue() && !m_splitVscp && nodep->varp()->attrIsolateAssign()) {
            m_splitVscp = nodep->varScopep();
        }
    }
    virtual void visit(AstNode* nodep) override { iterateChildren(nodep); }

public:
    // CONSTRUCTORS
    explicit SplitAsFindVisitor(AstAlways* nodep) { iterate(nodep); }
    virtual ~SplitAsFindVisitor() override {}
    // METHODS
    AstVarScope* splitVscp() const { return m_splitVscp; }
};

//######################################################################
// Remove nodes not containing proper references

class SplitAsCleanVisitor : public SplitAsBaseVisitor {
private:
    // STATE
    AstVarScope* m_splitVscp;  // Variable we want to split
    bool m_modeMatch;  // Remove matching Vscp, else non-matching
    bool m_keepStmt = false;  // Current Statement must be preserved
    bool m_matches = false;  // Statement below has matching lvalue reference

    // METHODS
    virtual void visit(AstVarRef* nodep) override {
        if (nodep->lvalue()) {
            if (nodep->varScopep() == m_splitVscp) {
                UINFO(6, "       CL VAR " << nodep << endl);
                m_matches = true;
            }
        }
    }
    virtual void visit(AstNodeStmt* nodep) override {
        if (!nodep->isStatement()) {
            iterateChildren(nodep);
            return;
        }
        UINFO(6, "     CL STMT " << nodep << endl);
        bool oldKeep = m_keepStmt;
        {
            m_matches = false;
            m_keepStmt = false;

            iterateChildren(nodep);

            if (m_keepStmt || (m_modeMatch ? m_matches : !m_matches)) {
                UINFO(6, "     Keep   STMT " << nodep << endl);
                m_keepStmt = true;
            } else {
                UINFO(6, "     Delete STMT " << nodep << endl);
                nodep->unlinkFrBack();
                pushDeletep(nodep);
            }
        }
        // If something below matches, the upper statement remains too.
        m_keepStmt = oldKeep || m_keepStmt;
        UINFO(9, "     upKeep=" << m_keepStmt << " STMT " << nodep << endl);
    }
    virtual void visit(AstNode* nodep) override { iterateChildren(nodep); }

public:
    // CONSTRUCTORS
    SplitAsCleanVisitor(AstAlways* nodep, AstVarScope* vscp, bool modeMatch)
        : m_splitVscp{vscp}
        , m_modeMatch{modeMatch} {
        iterate(nodep);
    }
    virtual ~SplitAsCleanVisitor() override {}
};

//######################################################################
// SplitAs class functions

class SplitAsVisitor : public SplitAsBaseVisitor {
private:
    // NODE STATE
    //  AstAlways::user()       -> bool.  True if already processed
    AstUser1InUse m_inuser1;

    // STATE
    VDouble0 m_statSplits;  // Statistic tracking
    AstVarScope* m_splitVscp = nullptr;  // Variable we want to split

    // METHODS
    void splitAlways(AstAlways* nodep) {
        UINFO(3, "Split  " << nodep << endl);
        UINFO(3, "   For " << m_splitVscp << endl);
        if (debug() >= 9) nodep->dumpTree(cout, "-in  : ");
        // Duplicate it and link in
        AstAlways* newp = nodep->cloneTree(false);
        newp->user1(true);  // So we don't clone it again
        nodep->addNextHere(newp);
        {  // Delete stuff we don't want in old
            SplitAsCleanVisitor visitor(nodep, m_splitVscp, false);
            if (debug() >= 9) nodep->dumpTree(cout, "-out0: ");
        }
        {  // Delete stuff we don't want in new
            SplitAsCleanVisitor visitor(newp, m_splitVscp, true);
            if (debug() >= 9) newp->dumpTree(cout, "-out1: ");
        }
    }

    virtual void visit(AstAlways* nodep) override {
        // Are there any lvalue references below this?
        // There could be more than one.  So, we process the first one found first.
        AstVarScope* lastSplitVscp = nullptr;
        while (!nodep->user1()) {
            // Find any splittable variables
            SplitAsFindVisitor visitor(nodep);
            m_splitVscp = visitor.splitVscp();
            if (m_splitVscp && m_splitVscp == lastSplitVscp) {
                // We did this last time!  Something's stuck!
                nodep->v3fatalSrc("Infinite loop in isolate_assignments removal for: "
                                  << m_splitVscp->prettyNameQ());
            }
            lastSplitVscp = m_splitVscp;
            // Now isolate the always
            if (m_splitVscp) {
                splitAlways(nodep);
                ++m_statSplits;
            } else {
                nodep->user1(true);
            }
        }
    }

    // Speedup; no always under math
    virtual void visit(AstNodeMath*) override {}
    virtual void visit(AstNode* nodep) override { iterateChildren(nodep); }

public:
    // CONSTRUCTORS
    explicit SplitAsVisitor(AstNetlist* nodep) {
        AstNode::user1ClearTree();  // user1p() used on entire tree
        iterate(nodep);
    }
    virtual ~SplitAsVisitor() override {
        V3Stats::addStat("Optimizations, isolate_assignments blocks", m_statSplits);
    }
};

//######################################################################
// SplitAs class functions

void V3SplitAs::splitAsAll(AstNetlist* nodep) {
    UINFO(2, __FUNCTION__ << ": " << endl);
    { SplitAsVisitor visitor(nodep); }  // Destruct before checking
    V3Global::dumpCheckGlobalTree("splitas", 0, v3Global.opt.dumpTreeLevel(__FILE__) >= 3);
}