verilator/src/V3SplitAs.cpp

// -*- mode: C++; c-file-style: "cc-mode" -*-
//*************************************************************************
// DESCRIPTION: Verilator: Break always into separate statements to reduce temps
//
// Code available from: http://www.veripool.org/verilator
//
//*************************************************************************
//
// Copyright 2003-2018 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.
//
// Verilator is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
//*************************************************************************
// 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 <cstdio>
#include <cstdarg>
#include <unistd.h>
#include <algorithm>
#include <vector>
#include <map>

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

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

class SplitAsBaseVisitor : public AstNVisitor {
public:
    // METHODS
    static int debug() {
	static int level = -1;
	if (VL_UNLIKELY(level < 0)) level = v3Global.opt.debugSrcLevel(__FILE__);
	return level;
    }
};

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

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

    // METHODS
    virtual void visit(AstVarRef* nodep) {
	if (nodep->lvalue() && !m_splitVscp
	    && nodep->varp()->attrIsolateAssign()) {
	    m_splitVscp = nodep->varScopep();
	}
    }
    virtual void visit(AstNode* nodep) {
	nodep->iterateChildren(*this);
    }
public:
    // CONSTUCTORS
    explicit SplitAsFindVisitor(AstAlways* nodep) {
	m_splitVscp = NULL;
	nodep->accept(*this);
    }
    virtual ~SplitAsFindVisitor() {}
    // 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;	// Current Statement must be preserved
    bool	 m_matches;	// Statement below has matching lvalue reference

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

	    nodep->iterateChildren(*this);

	    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) {
	nodep->iterateChildren(*this);
    }
public:
    // CONSTUCTORS
    SplitAsCleanVisitor(AstAlways* nodep, AstVarScope* vscp, bool modeMatch) {
	m_splitVscp = vscp;
	m_modeMatch = modeMatch;
	nodep->accept(*this);
    }
    virtual ~SplitAsCleanVisitor() {}
};

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

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

    // STATE
    V3Double0	m_statSplits;	// Statistic tracking
    AstVarScope* m_splitVscp;	// 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) {
	// Are there any lvalue references below this?
	// There could be more than one.  So, we process the first one found first.
	AstVarScope* lastSplitVscp = NULL;
	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->prettyName())
		m_splitVscp = NULL;
	    }
	    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* nodep) {}

    virtual void visit(AstNode* nodep) {
	nodep->iterateChildren(*this);
    }

public:
    // CONSTUCTORS
    explicit SplitAsVisitor(AstNetlist* nodep) {
	m_splitVscp = NULL;
	AstNode::user1ClearTree();	// user1p() used on entire tree
	nodep->accept(*this);
    }
    virtual ~SplitAsVisitor() {
	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);
}