verilator/src/V3Life.cpp

//*************************************************************************
// DESCRIPTION: Verilator: Lifelicate variable assignment elimination
//
// 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.
//
//*************************************************************************
// LIFE TRANSFORMATIONS:
//	Build control-flow graph with assignments and var usages
//	All modules:
//	    ASSIGN(x,...), ASSIGN(x,...) => delete first one
//	    We also track across if statements:
//	    ASSIGN(X,...) IF( ..., ASSIGN(X,...), ASSIGN(X,...)) => deletes first
//	    We don't do the opposite yet though (remove assigns in if followed by outside if)
//
//*************************************************************************

#include "config_build.h"
#include "verilatedos.h"
#include <cstdio>
#include <cstdarg>
#include <unistd.h>
#include <map>

#include "V3Global.h"
#include "V3Life.h"
#include "V3Stats.h"
#include "V3Ast.h"
#include "V3Const.h"

//######################################################################
// Structure for global state

class LifeState {
    // NODE STATE
    //   See below
    AstUserInUse	m_inuse1;

    // STATE
public:
    V3Double0	m_statAssnDel;	// Statistic tracking
    V3Double0	m_statAssnCon;	// Statistic tracking

public:
    LifeState() {}
    ~LifeState() {
	V3Stats::addStat("Optimizations, Lifetime assign deletions", m_statAssnDel);
	V3Stats::addStat("Optimizations, Lifetime constant prop", m_statAssnCon);
    }
};

//######################################################################
// Structure for each variable encountered

class LifeVarEntry {
    AstNodeAssign*	m_assignp;	// Last assignment to this varscope, NULL if no longer relevant
    AstConst*		m_constp;	// Known constant value
    bool		m_setBeforeUse;	// First access was a set (and thus block above may have a set that can be deleted
    bool		m_everSet;	// Was ever assigned (and thus above block may not preserve constant propagation)

    inline void init (bool setBeforeUse) {
	m_assignp = NULL;
	m_constp = NULL;
	m_setBeforeUse = setBeforeUse;
	m_everSet = false;
    }
public:
    class SIMPLEASSIGN {};
    class COMPLEXASSIGN {};
    class CONSUMED {};

    LifeVarEntry(SIMPLEASSIGN, AstNodeAssign* assp) {
	init(true); simpleAssign(assp);
    }
    LifeVarEntry(COMPLEXASSIGN) {
	init(false); complexAssign();
    }
    LifeVarEntry(CONSUMED) {
	init(false); consumed();
    }
    ~LifeVarEntry() {}
    inline void simpleAssign(AstNodeAssign* assp) { // New simple A=.... assignment
	m_assignp = assp;
	m_constp = NULL;
	m_everSet = true;
	if (assp->rhsp()->castConst()) m_constp = assp->rhsp()->castConst();
    }
    inline void complexAssign() {  // A[x]=... or some complicated assignment
	m_assignp = NULL;
	m_constp = NULL;
	m_everSet = true;
    }
    inline void consumed() {  // Rvalue read of A
	m_assignp = NULL;
    }
    AstNodeAssign* assignp() const { return m_assignp; }
    AstConst* constNodep() const { return m_constp; }
    bool setBeforeUse() const { return m_setBeforeUse; }
    bool everSet() const { return m_everSet; }
};

//######################################################################
// Structure for all variables under a given meta-basic block

class LifeBlock {
    // NODE STATE
    // Cleared each AstIf:
    //   AstVarScope::user()	-> int.       Used in combining to detect duplicates

    // LIFE MAP
    //  For each basic block, we'll make a new map of what variables that if/else is changing
    typedef std::map<AstVarScope*, LifeVarEntry> LifeMap;
    LifeMap	m_map;		// Current active lifetime map for current scope
    LifeBlock*	m_aboveLifep;	// Upper life, or NULL
    LifeState*	m_statep;	// Current global state

public:
    LifeBlock(LifeBlock* aboveLifep, LifeState* statep) {
	m_aboveLifep = aboveLifep;  // Null if top
	m_statep = statep;
    }
    ~LifeBlock() {}
    // METHODS
    void checkRemoveAssign(const LifeMap::iterator& it) {
	AstVar* varp = it->first->varp();
	LifeVarEntry* entp = &(it->second);
	if (!varp->isSigPublic()) {
	    // Rather than track what sigs AstUCFunc/AstUCStmt may change,
	    // we just don't optimize any public sigs
	    // Check the var entry, and remove if appropriate
	    if (AstNode* oldassp = entp->assignp()) {
		UINFO(7,"       PREV: "<<oldassp<<endl);
		// Redundant assignment, in same level block
		if (debug()>4) oldassp->dumpTree(cout, "       REMOVE/SAMEBLK ");
		entp->complexAssign();
		oldassp->unlinkFrBack()->deleteTree(); oldassp=NULL;
		m_statep->m_statAssnDel++;
	    }
	}
    }
    void simpleAssign(AstVarScope* nodep, AstNodeAssign* assp) {
	// Do we have a old assignment we can nuke?
	UINFO(4,"     ASSIGNof: "<<nodep<<endl);
	UINFO(7,"       new: "<<assp<<endl);
	LifeMap::iterator it = m_map.find(nodep);
	if (it != m_map.end()) {
	    checkRemoveAssign(it);
	    it->second.simpleAssign(assp);
	} else {
	    m_map.insert(make_pair(nodep,LifeVarEntry(LifeVarEntry::SIMPLEASSIGN(), assp)));
	}
	//lifeDump();
    }
    void complexAssign(AstVarScope* nodep) {
	UINFO(4,"     clearof: "<<nodep<<endl);
	LifeMap::iterator it = m_map.find(nodep);
	if (it != m_map.end()) {
	    it->second.complexAssign();
	} else {
	    m_map.insert(make_pair(nodep,LifeVarEntry(LifeVarEntry::COMPLEXASSIGN())));
	}
    }
    void varUsageReplace (AstVarScope* nodep, AstVarRef* varrefp) {
	// Variable rvalue.  If it references a constant, we can simply replace it
	LifeMap::iterator it = m_map.find(nodep);
	if (it != m_map.end()) {
	    if (AstConst* constp = it->second.constNodep()) {
		if (!varrefp->varp()->isSigPublic()) {
		    // Aha, variable is constant; substitute in.
		    // We'll later constant propagate
		    UINFO(4,"     replaceconst: "<<varrefp<<endl);
		    varrefp->replaceWith(constp->cloneTree(false));
		    varrefp->deleteTree(); varrefp=NULL;
		    m_statep->m_statAssnCon++;
		    return;  // **DONE, no longer a var reference**
		}
	    }
	    UINFO(4,"     usage: "<<nodep<<endl);
	    it->second.consumed();
	} else {
	    m_map.insert(make_pair(nodep,LifeVarEntry(LifeVarEntry::CONSUMED())));
	}
    }
    void complexAssignFind(AstVarScope* nodep) {
	LifeMap::iterator it = m_map.find(nodep);
	if (it != m_map.end()) {
	    UINFO(4,"     casfind: "<<it->first<<endl);
	    it->second.complexAssign();
	} else {
	    m_map.insert(make_pair(nodep,LifeVarEntry(LifeVarEntry::COMPLEXASSIGN())));
	}
    }
    void consumedFind(AstVarScope* nodep) {
	LifeMap::iterator it = m_map.find(nodep);
	if (it != m_map.end()) {
	    it->second.consumed();
	} else {
	    m_map.insert(make_pair(nodep,LifeVarEntry(LifeVarEntry::CONSUMED())));
	}
    }
    void lifeToAbove() {
	// Any varrefs under a if/else branch affect statements outside and after the if/else
	if (!m_aboveLifep) v3fatalSrc("Pushing life when already at the top level");
	for (LifeMap::iterator it = m_map.begin(); it!=m_map.end(); ++it) {
	    AstVarScope* nodep = it->first;
	    m_aboveLifep->complexAssignFind(nodep);
	    if (it->second.everSet()) {
		// Record there may be an assignment, so we don't constant propagate across the if.
		complexAssignFind(nodep);
	    } else {
		// Record consumption, so we don't eliminate earlier assignments
		consumedFind(nodep);
	    }
	}
    }
    void dualBranch (LifeBlock* life1p, LifeBlock* life2p) {
	// Find any common sets on both branches of IF and propagate upwards
	//life1p->lifeDump();
	//life2p->lifeDump();
	AstNode::userClearTree();	// userp() used on entire tree
	for (LifeMap::iterator it = life1p->m_map.begin(); it!=life1p->m_map.end(); ++it) {
	    // When the if branch sets a var before it's used, mark that variable
	    if (it->second.setBeforeUse()) it->first->user(1);
	}
	for (LifeMap::iterator it = life2p->m_map.begin(); it!=life2p->m_map.end(); ++it) {
	    // When the else branch sets a var before it's used
	    AstVarScope* nodep = it->first;
	    if (it->second.setBeforeUse() && nodep->user()) {
		// Both branches set the var, we can remove the assignment before the IF.
		UINFO(4,"DUALBRANCH "<<nodep<<endl);
		LifeMap::iterator itab = m_map.find(nodep);
		if (itab != m_map.end()) {
		    checkRemoveAssign(itab);
		}
	    }
	}
	//this->lifeDump();
    }
    // DEBUG
    void lifeDump() {
	UINFO(5, "  LifeMap:"<<endl);
	for (LifeMap::iterator it = m_map.begin(); it!=m_map.end(); ++it) {
	    UINFO(5, "     Ent:  "
		  <<(it->second.setBeforeUse()?"[F]  ":"     ")
		  <<it->first<<endl);
	    if (it->second.assignp()) {
		UINFO(5, "       Ass: "<<it->second.assignp()<<endl);
	    }
	}
    }
};

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

class LifeVisitor : public AstNVisitor {
private:
    // STATE
    LifeState*	m_statep;	// Current state
    bool	m_sideEffect;	// Side effects discovered in assign RHS
    //static int debug() { return 9; }

    // LIFE MAP
    //  For each basic block, we'll make a new map of what variables that if/else is changing
    typedef std::map<AstVarScope*, LifeVarEntry> LifeMap;
    LifeBlock*	m_lifep;	// Current active lifetime map for current scope

    // METHODS
    // VISITORS
    virtual void visit(AstVarRef* nodep, AstNUser*) {
	// Consumption/generation of a variable,
	// it's used so can't elim assignment before this use.
	if (!nodep->varScopep()) nodep->v3fatalSrc("NULL");
	//
	AstVarScope* vscp = nodep->varScopep();
	if (!vscp) nodep->v3fatalSrc("Scope not assigned");
	if (nodep->lvalue()) {
	    m_lifep->complexAssign(vscp);
	} else {
	    m_lifep->varUsageReplace(vscp, nodep); nodep=NULL;
	}
    }
    virtual void visit(AstNodeAssign* nodep, AstNUser*) {
	// Collect any used variables first, as lhs may also be on rhs
	// Similar code in V3Dead
	vluint64_t lastEdit = AstNode::editCountGbl();	// When it was last edited
	m_sideEffect = false;
	nodep->rhsp()->iterateAndNext(*this);
	if (lastEdit != AstNode::editCountGbl()) {
	    // We changed something, try to constant propagate, but don't delete the
	    // assignment as we still need nodep to remain.
	    V3Const::constifyTree(nodep->rhsp());
	}
	// Has to be direct assignment without any EXTRACTing.
	if (nodep->lhsp()->castVarRef() && !m_sideEffect) {
	    AstVarScope* vscp = nodep->lhsp()->castVarRef()->varScopep();
	    if (!vscp) vscp->v3fatalSrc("Scope lost on variable");
	    m_lifep->simpleAssign(vscp, nodep);
	} else {
	    nodep->lhsp()->iterateAndNext(*this);
	}
    }
    virtual void visit(AstAssignDly* nodep, AstNUser*) {
	// Don't treat as normal assign; V3Life doesn't understand time sense
	nodep->iterateChildren(*this);
    }

    //---- Track control flow changes
    virtual void visit(AstNodeIf* nodep, AstNUser*) {
	UINFO(4,"   IF "<<nodep<<endl);
	// Condition is part of PREVIOUS block
	nodep->condp()->iterateAndNext(*this);
	LifeBlock* prevLifep = m_lifep;
	LifeBlock* ifLifep   = new LifeBlock (prevLifep, m_statep);
	LifeBlock* elseLifep = new LifeBlock (prevLifep, m_statep);
	{
	    m_lifep = ifLifep;
	    nodep->ifsp()->iterateAndNext(*this);
	    m_lifep = prevLifep;
	}
	{
	    m_lifep = elseLifep;
	    nodep->elsesp()->iterateAndNext(*this);
	    m_lifep = prevLifep;
	}
	UINFO(4,"   join "<<endl);
	// Find sets on both flows
	m_lifep->dualBranch (ifLifep, elseLifep);
	// For the next assignments, clear any variables that were read or written in the block
	ifLifep->lifeToAbove();
	elseLifep->lifeToAbove();
	delete ifLifep;
	delete elseLifep;
    }

    virtual void visit(AstWhile* nodep, AstNUser*) {
	// While's are a problem, as we don't allow loops in the graph.  We
	// may go around the cond/body multiple times.  Thus a
	// lifelication just in the body is ok, but we can't delete an
	// assignment in the body that's used in the cond.  (And otherwise
	// would because it only appears used after-the-fact.  So, we model
	// it as a IF statement, and just don't allow elimination of
	// variables across the body.
	LifeBlock* prevLifep = m_lifep;
	LifeBlock* condLifep = new LifeBlock (prevLifep, m_statep);
	LifeBlock* bodyLifep = new LifeBlock (prevLifep, m_statep);
	{
	    m_lifep = condLifep;
	    nodep->precondsp()->iterateAndNext(*this);
	    nodep->condp()->iterateAndNext(*this);
	    m_lifep = prevLifep;
	}
	{
	    m_lifep = bodyLifep;
	    nodep->bodysp()->iterateAndNext(*this);
	    m_lifep = prevLifep;
	}
	UINFO(4,"   joinfor"<<endl);
	// For the next assignments, clear any variables that were read or written in the block
	condLifep->lifeToAbove();
	bodyLifep->lifeToAbove();
	delete condLifep;
	delete bodyLifep;
    }
    virtual void visit(AstCCall* nodep, AstNUser*) {
	//UINFO(4,"  CCALL "<<nodep<<endl);
	nodep->iterateChildren(*this);
	// Enter the function and trace it
	if (!nodep->funcp()->entryPoint()) {  // else is non-inline or public function we optimize separately
	    nodep->funcp()->accept(*this);
	}
    }
    virtual void visit(AstUCFunc* nodep, AstNUser*) {
	m_sideEffect = true;  // If appears on assign RHS, don't ever delete the assignment
	nodep->iterateChildren(*this);
    }

    virtual void visit(AstVar*, AstNUser*) {}	// Don't want varrefs under it
    virtual void visit(AstNode* nodep, AstNUser*) {
	nodep->iterateChildren(*this);
    }

public:
    // CONSTRUCTORS
    LifeVisitor(AstNode* nodep, LifeState* statep) {
	UINFO(4,"  LifeVisitor on "<<nodep<<endl);
	m_statep = statep;
	m_sideEffect = false;
	{
	    m_lifep = new LifeBlock (NULL, m_statep);
	    nodep->accept(*this);
	    delete m_lifep; m_lifep=NULL;
	}
    }
    virtual ~LifeVisitor() {}
};

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

class LifeTopVisitor : public AstNVisitor {
    // Visit all top nodes searching for functions that are entry points we want to start
    // finding code within.
private:
    // STATE
    LifeState* m_statep;	// Current state

    // VISITORS
    virtual void visit(AstCFunc* nodep, AstNUser*) {
	if (nodep->entryPoint()) {
	    // Usage model 1: Simulate all C code, doing lifetime analysis
	    LifeVisitor visitor (nodep, m_statep);
	}
    }
    virtual void visit(AstAlways* nodep, AstNUser*) {
	// Usage model 2: Cleanup basic blocks
	LifeVisitor visitor (nodep, m_statep);
    }
    virtual void visit(AstInitial* nodep, AstNUser*) {
	// Usage model 2: Cleanup basic blocks
	LifeVisitor visitor (nodep, m_statep);
    }
    virtual void visit(AstFinal* nodep, AstNUser*) {
	// Usage model 2: Cleanup basic blocks
	LifeVisitor visitor (nodep, m_statep);
    }
    virtual void visit(AstVar*, AstNUser*) {}		// Accelerate
    virtual void visit(AstNodeStmt*, AstNUser*) {}	// Accelerate
    virtual void visit(AstNodeMath*, AstNUser*) {}	// Accelerate
    virtual void visit(AstNode* nodep, AstNUser*) {
	nodep->iterateChildren(*this);
    }
public:
    // CONSTRUCTORS
    LifeTopVisitor(AstNetlist* nodep, LifeState* statep) {
	m_statep = statep;
	nodep->accept(*this);
    }
    virtual ~LifeTopVisitor() {}
};

//######################################################################
// Life class functions

void V3Life::lifeAll(AstNetlist* nodep) {
    UINFO(2,__FUNCTION__<<": "<<endl);
    LifeState state;
    LifeTopVisitor visitor (nodep, &state);
}