verilator/src/V3Unroll.cpp

//*************************************************************************
// DESCRIPTION: Verilator: Add temporaries, such as for unroll nodes
//
// Code available from: http://www.veripool.org/verilator
//
// AUTHORS: Wilson Snyder with Paul Wasson, Duane Gabli
//
//*************************************************************************
//
// Copyright 2003-2008 by Wilson Snyder.  This program is free software; you can
// redistribute it and/or modify it under the terms of either the GNU
// General Public License or the Perl Artistic License.
//
// 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.
//
//*************************************************************************
// V3Unroll's Transformations:
//	Note is called twice.  Once on modules for GenFor unrolling,
//	Again after V3Scope for normal for loop unrolling.
//
// Each module:
//	Look for "FOR" loops and unroll them if <= 32 loops.
//	(Eventually, a better way would be to simulate the entire loop; ala V3Table.)
//	Convert remaining FORs to WHILEs
//
//*************************************************************************

#include "config_build.h"
#include "verilatedos.h"
#include <cstdio>
#include <cstdarg>
#include <unistd.h>
#include <algorithm>

#include "V3Global.h"
#include "V3Unroll.h"
#include "V3Stats.h"
#include "V3Const.h"
#include "V3Ast.h"

//######################################################################
// Unroll state, as a visitor of each AstNode

class UnrollVisitor : public AstNVisitor {
private:
    // STATE
    AstVar*		m_forVarp;		// Iterator variable
    AstVarScope*	m_forVscp;		// Iterator variable scope (NULL for generate pass)
    AstConst*		m_varValuep;		// Current value of loop
    AstNode*		m_ignoreIncp;		// Increment node to ignore
    bool		m_varModeCheck;		// Just checking RHS assignments
    bool		m_varModeReplace;	// Replacing varrefs
    bool		m_varAssignHit;		// Assign var hit
    bool		m_inBegin;		// Inside a begin/end loop
    bool		m_generate;		// Expand single generate For loop
    V3Double0		m_statLoops;		// Statistic tracking
    V3Double0		m_statIters;		// Statistic tracking

    //int debug() { return 9; }

    // VISITORS
    virtual void visit(AstModule* nodep, AstNUser*) {
	UINFO(4," MOD   "<<nodep<<endl);
	nodep->iterateChildren(*this);
    }

    bool cantUnroll(AstNode* nodep, const char* reason) {
	if (m_generate) {
	    nodep->v3error("Unsupported: Can't unroll generate for; "<<reason);
	}
	UINFO(3,"   Can't Unroll: "<<reason<<" :"<<nodep<<endl);
	V3Stats::addStatSum(string("Unrolling gave up, ")+reason, 1);
	return false;
    }

    int unrollCount() {
	return m_generate ? v3Global.opt.unrollCount()*16
	    : v3Global.opt.unrollCount();
    }

    bool forUnrollCheck(AstNode* nodep,
			AstNode* initp,	// Maybe under nodep (no nextp), or standalone (ignore nextp)
			AstNode* precondsp, AstNode* condp,
			AstNode* incp,		// Maybe under nodep or in bodysp
			AstNode* bodysp) {
	// To keep the IF levels low, we return as each test fails.
	UINFO(4, " FOR Check "<<nodep<<endl);
	if (initp)	UINFO(6, "    Init "<<initp<<endl);
	if (precondsp)	UINFO(6, "    Pcon "<<precondsp<<endl);
	if (condp)	UINFO(6, "    Cond "<<condp<<endl);
	if (incp)	UINFO(6, "    Inc  "<<incp<<endl);
	// Initial value check
	AstAssign* initAssp = initp->castAssign();
	if (!initAssp) return cantUnroll(nodep, "no initial assignment");
	if (initp->nextp() && initp->nextp()!=nodep) nodep->v3fatalSrc("initial assignment shouldn't be a list");
	m_forVarp = initAssp->lhsp()->castVarRef()->varp();
	m_forVscp = initAssp->lhsp()->castVarRef()->varScopep();
	if (nodep->castGenFor() && !m_forVarp->isGenVar()) {
	    nodep->v3error("Non-genvar used in generate for: "<<m_forVarp->name()<<endl);
	}
	if (m_generate) V3Const::constifyParam(initAssp->rhsp());
	AstConst* constInitp = initAssp->rhsp()->castConst();
	if (!constInitp) return cantUnroll(nodep, "non-constant initializer");
	//
	// Condition check
	if (condp->nextp()) nodep->v3fatalSrc("conditional shouldn't be a list");
	//
	// Assignment of next value check
	AstAssign* incAssp = incp->castAssign();
	if (!incAssp) return cantUnroll(nodep, "no increment assignment");
	if (incAssp->nextp()) nodep->v3fatalSrc("increment shouldn't be a list");
	AstNodeBiop* incInstrp = incAssp->rhsp()->castNodeBiop();
	//
	if (m_forVscp) { UINFO(8, "   Loop Variable: "<<m_forVscp<<endl); }
	else	       { UINFO(8, "   Loop Variable: "<<m_forVarp<<endl); }
	if (debug()>=9) nodep->dumpTree(cout,"-   for: ");
	//
	// Extract the constant loop bounds
	bool subtract = incInstrp->castSub();
	{
	    if (!subtract && !incInstrp->castAdd()) return cantUnroll(nodep, "missing add/sub for incrementer");
	    AstVarRef* incVarrp   = (subtract ? incInstrp->lhsp()->castVarRef()
				     : incInstrp->rhsp()->castVarRef());
	    if (!incVarrp) return cantUnroll(nodep, "missing variable in incrementer");
	    if (incVarrp->varp() != m_forVarp
		|| incVarrp->varScopep() != m_forVscp) {
		return cantUnroll(nodep, "different variables in incrementer");
	    }
	}
	//
	// Adds have the # on the lhsp because V3Const pushes rhs consts over to the lhs
	// Subtracts have it on the rhs, because you write i=i-1; i=1-i is non-sensible.
	AstConst* preconstIncp = (subtract ? incInstrp->rhsp()->castConst()
				  : incInstrp->lhsp()->castConst());
	if (m_generate) V3Const::constifyParam(preconstIncp);
	AstConst* constIncp = (subtract ? incInstrp->rhsp()->castConst()
			       : incInstrp->lhsp()->castConst());
	UINFO(8, "   Inc expr ok:  "<<constIncp<<endl);
	if (!constIncp) return cantUnroll(nodep, "non-constant increment");
	if (constIncp->isZero()) return cantUnroll(nodep, "zero increment");  // Or we could loop forever below...

        bool lt  = condp->castLt() || condp->castLtS();
        bool lte = condp->castLte() || condp->castLteS();
	bool gt  = condp->castGt() || condp->castGtS();
	bool gte = condp->castGte() || condp->castGteS();
	if (!lt && !lte && !gt && !gte)
	    return cantUnroll(nodep, "condition not <= or <");
	AstNodeBiop* condBip = condp->castNodeBiop();
	if (!condBip->lhsp()->castVarRef())
	    return cantUnroll(nodep, "no variable on lhs of condition");
	if (condBip->lhsp()->castVarRef()->varp() != m_forVarp
	    || condBip->lhsp()->castVarRef()->varScopep() != m_forVscp)
	    return cantUnroll(nodep, "different variable in condition");
	if (m_generate) V3Const::constifyParam(condBip->rhsp());
	AstConst* constStopp = condBip->rhsp()->castConst();
	if (!constStopp) return cantUnroll(nodep, "non-constant final value");
	UINFO(8, "   Stop expr ok: "<<constStopp<<endl);
	//
	if (constInitp->width()>32 || constInitp->num().isFourState()
	    || constStopp->width()>32 || constStopp->num().isFourState()
	    || constIncp->width()>32  || constIncp->num().isFourState())
	    return cantUnroll(nodep, "init/final/increment too large or four state");
	vlsint32_t valInit = constInitp->num().toSInt();
	vlsint32_t valStop = constStopp->num().toSInt();
	if (lte) valStop++;  if (gte) valStop--;
	vlsint32_t valInc  = constIncp->num().toSInt();
	if (subtract) valInc = -valInc;
	UINFO(8,"     In Numbers: for (v="<<valInit<<"; v<"<<valStop<<"; v=v+"<<valInc<<")\n");
	//
	if (!m_generate) {
	    UINFO(8, "         ~Iters: "<<((valStop - valInit)/valInc)<<" c="<<unrollCount()<<endl);
	    if (((valStop - valInit)/valInc) > unrollCount())
		return cantUnroll(nodep, "too many iterations");

	    // Less than 10 statements in the body?
	    int bodySize = 0;
	    for (AstNode* bodp = precondsp; bodp; bodp=bodp->nextp()) {
		bodySize++;
	    }
	    for (AstNode* bodp = bodysp; bodp; bodp=bodp->nextp()) {
		bodySize++;
	    }
	    if (bodySize > v3Global.opt.unrollStmts())
		return cantUnroll(nodep, "too many statements");
	}
	//
	// Now, make sure there's no assignment to this variable in the loop
	m_varModeCheck = true;
	m_varAssignHit = false;
	m_ignoreIncp = incp;
	precondsp->iterateAndNext(*this);
	bodysp->iterateAndNext(*this);
	m_varModeCheck = false;
	m_ignoreIncp = NULL;
	if (m_varAssignHit) return cantUnroll(nodep, "genvar assigned *inside* loop");
	//
	// Finally, we can do it
	forUnroller(nodep, initp, precondsp, condp, incp, bodysp,
		    constInitp->num(),
		    condBip, constStopp->num(),
		    incInstrp, constIncp->num()); nodep = NULL;
	// Cleanup
	return true;
    }

    void forUnroller(AstNode* nodep,
		     AstNode* initp,
		     AstNode* precondsp, AstNode* condp,
		     AstNode* incp, AstNode* bodysp,
		     const V3Number& numInit,
		     AstNodeBiop* cmpInstrp, const V3Number& numStop,
		     AstNodeBiop* incInstrp, const V3Number& numInc) {
	UINFO(4, "   Unroll for var="<<numInit<<"; var<"<<numStop<<"; var+="<<numInc<<endl);
	UINFO(6, "    cmpI "<<cmpInstrp<<endl);
	UINFO(6, "    IncI "<<incInstrp<<endl);
	AstNode* stmtsp = NULL;
	if (initp) {
	    initp->unlinkFrBack();	// Always a single statement; nextp() may be nodep
	    // Don't add to list, we do it once, and setting loop index isn't needed as we're constant propagating it
	}
	if (precondsp) {
	    precondsp->unlinkFrBackWithNext();
	    stmtsp = stmtsp->addNextNull(precondsp);
	}
	if (bodysp) {
	    bodysp->unlinkFrBackWithNext();
	    stmtsp = stmtsp->addNextNull(bodysp);  // Maybe null if no body
	}
	// If it's a While, then incp is already part of bodysp.
	V3Number loopValue(nodep->fileline(), m_forVarp->width());  // May differ in size from numInitp
	loopValue.opAssign(numInit);

	AstNode* newbodysp = NULL;
	m_statLoops++;
	if (stmtsp) {
	    int times = 0;
	    while (1) {
		UINFO(8,"      Looping "<<loopValue<<endl);
		// if loopValue<valStop
		V3Number contin (nodep->fileline(), 1);
		cmpInstrp->numberOperate(contin, loopValue, numStop);
		if (contin.isEqZero()) {
		    break;  // Done with the loop
		} else {
		    // Replace iterator values with constant.
		    AstNode* oneloopp = stmtsp->cloneTree(true);

		    m_varValuep = new AstConst(nodep->fileline(), loopValue);

		    m_varModeReplace = true;
		    oneloopp->iterateAndNext(*this);
		    m_varModeReplace = false;

		    if (newbodysp) newbodysp->addNext(oneloopp);
		    else newbodysp = oneloopp;

		    m_statIters++;
		    if (++times > unrollCount()*3) {
			nodep->v3error("Loop unrolling took too long; probably this is an infinite loop, or set --unroll-count above "<<unrollCount());
			break;
		    }

		    //loopValue += valInc
		    V3Number newnum(nodep->fileline(), m_forVarp->width());  // Can't increment in-place
		    incInstrp->numberOperate(newnum, loopValue, numInc);
		    loopValue.opAssign(newnum);

		    pushDeletep(m_varValuep); m_varValuep=NULL;
		}
	    }
	}
	// Leaving the iterator at the final value is handled by the increment statements being left the final body
	// Replace the FOR()
	if (newbodysp) nodep->replaceWith(newbodysp);
	else nodep->unlinkFrBack();
	if (bodysp) { pushDeletep(bodysp); bodysp=NULL; }
	if (precondsp) { pushDeletep(precondsp); precondsp=NULL; }
	if (initp) { pushDeletep(initp); initp=NULL; }
	if (debug()>=9) newbodysp->dumpTree(cout,"-  _new: ");
    }

    virtual void visit(AstWhile* nodep, AstNUser*) {
	nodep->iterateChildren(*this);
	if (m_varModeCheck || m_varModeReplace) {
	} else {
	    // Constify before unroll call, as it may change what is underneath.
	    if (nodep->precondsp()) V3Const::constifyTree(nodep->precondsp());
	    if (nodep->condp()) V3Const::constifyTree(nodep->condp());
	    // Grab initial value
	    AstNode* initp = NULL;  // Should be statement before the while.
	    if (nodep->backp()->nextp() == nodep) initp=nodep->backp();
	    if (initp) V3Const::constifyTree(initp);
	    initp = NULL; if (nodep->backp()->nextp() == nodep) initp=nodep->backp();
	    // Grab assignment
	    AstNode* incp = NULL;  // Should be last statement
	    for (incp = nodep->bodysp(); incp && incp->nextp(); incp = incp->nextp()) {}
	    if (incp) V3Const::constifyTree(incp);
	    for (incp = nodep->bodysp(); incp && incp->nextp(); incp = incp->nextp()) {}  // Again, as may have changed
	    // And check it
	    if (forUnrollCheck(nodep, initp,
			       nodep->precondsp(), nodep->condp(),
			       incp, nodep->bodysp())) {
		pushDeletep(nodep); nodep=NULL; // Did replacement
	    }
	}
    }
    virtual void visit(AstGenFor* nodep, AstNUser*) {
	if (!m_generate || m_varModeReplace) {
	    nodep->iterateChildren(*this);
	}  // else V3Param will recursively call each for loop to be unrolled for us
	if (m_varModeCheck || m_varModeReplace) {
	} else {
	    // Constify before unroll call, as it may change what is underneath.
	    if (nodep->initsp()) V3Const::constifyTree(nodep->initsp());
	    if (nodep->condp()) V3Const::constifyTree(nodep->condp());
	    if (nodep->incsp()) V3Const::constifyTree(nodep->incsp());
	    if (nodep->condp()->isZero()) {
		// We don't need to do any loops.  Remove the GenFor,
		// Genvar's don't care about any initial assignments.
		//
		// Note normal For's can't do exactly this deletion, as
		// we'd need to initialize the variable to the initial
		// condition, but they'll become while's which can be
		// deleted by V3Const.
		nodep->unlinkFrBack()->deleteTree(); nodep=NULL;
	    } else if (forUnrollCheck(nodep, nodep->initsp(),
				      NULL, nodep->condp(),
				      nodep->incsp(), nodep->bodysp())) {
		pushDeletep(nodep); nodep=NULL; // Did replacement
	    } else {
		nodep->v3error("For loop doesn't have genvar index, or is misformed");
	    }
	}
    }
    virtual void visit(AstNodeFor* nodep, AstNUser*) {
	nodep->v3error("V3Task should have removed standard FORs");
    }

    virtual void visit(AstBegin* nodep, AstNUser*) {
	// Naming inside loop body; must have been a generate for.
	// We need to only rename the 'upper' begin,
	// anything lower will be renamed "uppernewname.lowerbegin"
	bool lastBegin = m_inBegin;
	m_inBegin = true;
	nodep->iterateChildren(*this);
	m_inBegin = lastBegin;

	if (m_varModeReplace && !m_inBegin // no upper begin, excluding this one
	    ) {
	    // Rename it, as otherwise we may get a conflict
	    // V3Begin sees these DOTs and makes CellInlines for us.
	    string index = AstNode::encodeNumber(m_varValuep->toSInt());
	    string nname = (string)"genfor"+index+"__DOT__"+nodep->name();
	    // Verilog seems to drop the for loop name and tack on [#]
	    nname = nodep->name() + "__BRA__" + index + "__KET__";
	    //UINFO(8,"   Rename begin "<<nname<<" "<<nodep<<endl);
	    nodep->name(nname);
	}
    }

    virtual void visit(AstVarRef* nodep, AstNUser*) {
	if (m_varModeCheck
	    && nodep->varp() == m_forVarp
	    && nodep->varScopep() == m_forVscp
	    && nodep->lvalue()) {
	    UINFO(8,"   Itervar assigned to: "<<nodep<<endl);
	    m_varAssignHit = true;
	}
	if (m_varModeReplace
	    && nodep->varp() == m_forVarp
	    && nodep->varScopep() == m_forVscp
	    && !nodep->lvalue()) {
	    AstNode* newconstp = m_varValuep->cloneTree(false);
	    nodep->replaceWith(newconstp);
	    pushDeletep(nodep);
	}
    }

    //--------------------
    // Default: Just iterate
    virtual void visit(AstNode* nodep, AstNUser*) {
	if (m_varModeCheck && nodep == m_ignoreIncp) {
	    // Ignore subtree that is the increment
	} else {
	    nodep->iterateChildren(*this);
	}
    }

public:
    // CONSTUCTORS
    UnrollVisitor(AstNode* nodep, bool generate) {
	m_forVarp = NULL;
	m_forVscp = NULL;
	m_ignoreIncp = NULL;
	m_varModeCheck = false;
	m_varModeReplace = false;
	m_inBegin = false;
	m_generate = generate;
	//
	nodep->accept(*this);
    }
    virtual ~UnrollVisitor() {
	V3Stats::addStat("Optimizations, Unrolled Loops", m_statLoops);
	V3Stats::addStat("Optimizations, Unrolled Iterations", m_statIters);
    }
};

//######################################################################
// Unroll class functions

void V3Unroll::unrollAll(AstNetlist* nodep) {
    UINFO(2,__FUNCTION__<<": "<<endl);
    UnrollVisitor visitor (nodep, false);
}

void V3Unroll::unrollGen(AstNodeFor* nodep) {
    UINFO(2,__FUNCTION__<<": "<<endl);
    UnrollVisitor visitor (nodep, true);
}