Redo V3Life to also do constant propagation

git-svn-id: file://localhost/svn/verilator/trunk/verilator@796 77ca24e4-aefa-0310-84f0-b9a241c72d87

Changes

@@ -9,6 +9,8 @@ indicates the contributor was also the author of the fix; Thanks!
 
 ***  Allow overriding Perl, Flex and Bison versions.  [by Robert Farrell]
 
+***  Optimize variables set to constants within basic blocks.
+
 **** Default make no longer makes the docs; if you edit the documentation
      sources, run "make info" to get them.
 

src/V3AstNodes.h

@@ -2776,6 +2776,7 @@ private:
     bool	m_funcPublic:1;		// From user public task/function
     bool	m_isStatic:1;		// Function is declared static (no this)
     bool	m_symProlog:1;		// Setup symbol table for later instructions
+    bool	m_entryPoint:1;		// User may call into this top level function
 public:
     AstCFunc(FileLine* fl, const string& name, AstScope* scopep, const string& rtnType="")
 	: AstNode(fl) {
@@ -2791,6 +2792,7 @@ public:
 	m_funcPublic = false;
 	m_isStatic = true;	// Note defaults to static, later we see where thisp is needed
 	m_symProlog = false;
+	m_entryPoint = false;
     }
     virtual ~AstCFunc() {}
     virtual AstType type() const { return AstType::CFUNC;}
@@ -2826,6 +2828,8 @@ public:
     void	isStatic(bool flag) { m_isStatic = flag; }
     bool	symProlog() const { return m_symProlog; }
     void	symProlog(bool flag) { m_symProlog = flag; }
+    bool	entryPoint() const { return m_entryPoint; }
+    void	entryPoint(bool flag) { m_entryPoint = flag; }
     //
     // If adding node accessors, see below
     AstNode*	argsp() 	const { return op1p()->castNode(); }

src/V3Clock.cpp

@@ -192,6 +192,7 @@ private:
 	    funcp->dontCombine(true);
 	    funcp->symProlog(true);
 	    funcp->isStatic(true);
+	    funcp->entryPoint(true);
 	    m_scopep->addActivep(funcp);
 	    m_evalFuncp = funcp;
 	}
@@ -202,6 +203,7 @@ private:
 	    funcp->slow(true);
 	    funcp->symProlog(true);
 	    funcp->isStatic(true);
+	    funcp->entryPoint(true);
 	    m_scopep->addActivep(funcp);
 	    m_initFuncp = funcp;
 	}
@@ -211,6 +213,7 @@ private:
 	    funcp->dontCombine(true);
 	    funcp->slow(true);
 	    funcp->isStatic(false);
+	    funcp->entryPoint(true);
 	    funcp->addInitsp(
 		new AstCStmt(nodep->fileline(),
 			     "    "+EmitCBaseVisitor::symClassVar()+" = this->__VlSymsp;\n"));
@@ -225,6 +228,7 @@ private:
 	    funcp->slow(true);
 	    funcp->isStatic(true);
 	    funcp->symProlog(true);
+	    funcp->entryPoint(true);
 	    m_scopep->addActivep(funcp);
 	    m_settleFuncp = funcp;
 	}

src/V3Life.cpp

@@ -38,152 +38,242 @@
 #include "V3Life.h"
 #include "V3Stats.h"
 #include "V3Ast.h"
+#include "V3Const.h"
 
 //######################################################################
-// Life state, as a visitor of each AstNode
+// Structure for global state
 
-class LifeVarEntry {
-    AstNode*	m_assignp;	// Last assignment to this varscope
-    bool	m_firstSet;	// True if creation was a set (and thus block above may have a set that can be deleted
+class LifeState {
+    // STATE
 public:
-    LifeVarEntry() {	// Construction for when a var is used
-	clearAssign();
-	m_firstSet = false;
+    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);
     }
-    LifeVarEntry(AstNode* assp) {	// Construction for when a var is set
-	m_assignp = assp;
-	m_firstSet = true;
-    }
-    LifeVarEntry(bool) {	// Construction for when a var is set, but ass isn't
-	m_assignp = NULL;
-	m_firstSet = true;
-    }
-    AstNode* assignp() const { return m_assignp; }
-    bool firstSet() const { return m_firstSet; }
-    void clearAssign() { m_assignp = NULL; }
-    void newerAssign(AstNode* assp) { m_assignp = assp; }
 };
 
-class LifeVisitor : public AstNVisitor {
-private:
-    // NODE STATE
-    //  AstVarScope::user()	-> int.       Used in combining to detect duplicates
+//######################################################################
+// Structure for each variable encountered
 
-    // STATE
-    //static int debug() { return 9; }
-    int		m_ifCount;	// If counter
-    V3Double0	m_statAssnDel;	// Statistic tracking
+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_lifep;	// Current active lifetime map for current scope
+    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(LifeVarEntry* entp) {
-	// 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->clearAssign();
-	    oldassp->unlinkFrBack();
-	    pushDeletep(oldassp);
-	    m_statAssnDel++;
+    void checkRemoveAssign(const LifeMap::iterator& it) {
+	AstVar* varp = it->first->varp();
+	LifeVarEntry* entp = &(it->second);
+	if (!varp->isSigPublic()) {
+	    // Rather then 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 setLast(AstVarScope* nodep, AstNode* assp) {
+    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 iter = m_lifep->find(nodep);
-	if (iter != m_lifep->end()) {
-	    checkRemoveAssign(&(iter->second));
-	    iter->second.newerAssign(assp);
+	LifeMap::iterator it = m_map.find(nodep);
+	if (it != m_map.end()) {
+	    checkRemoveAssign(it);
+	    it->second.simpleAssign(assp);
 	} else {
-	    m_lifep->insert(make_pair(nodep,LifeVarEntry(assp)));
+	    m_map.insert(make_pair(nodep,LifeVarEntry(LifeVarEntry::SIMPLEASSIGN(), assp)));
 	}
 	//lifeDump();
     }
-    void clearLastAssign(AstVarScope* nodep) {
+    void complexAssign(AstVarScope* nodep) {
 	UINFO(4,"     clearof: "<<nodep<<endl);
-	LifeMap::iterator iter = m_lifep->find(nodep);
-	if (iter != m_lifep->end()) {
-	    iter->second.clearAssign();
+	LifeMap::iterator it = m_map.find(nodep);
+	if (it != m_map.end()) {
+	    it->second.complexAssign();
 	} else {
-	    m_lifep->insert(make_pair(nodep,LifeVarEntry()));
+	    m_map.insert(make_pair(nodep,LifeVarEntry(LifeVarEntry::COMPLEXASSIGN())));
 	}
     }
-    void lifeDump(LifeMap* lifep) {
+    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 = lifep->begin(); it!=lifep->end(); ++it) {
+	for (LifeMap::iterator it = m_map.begin(); it!=m_map.end(); ++it) {
 	    UINFO(5, "     Ent:  "
-		  <<(it->second.firstSet()?"[F]  ":"     ")
+		  <<(it->second.setBeforeUse()?"[F]  ":"     ")
 		  <<it->first<<endl);
 	    if (it->second.assignp()) {
 		UINFO(5, "       Ass: "<<it->second.assignp()<<endl);
 	    }
 	}
     }
-    void clearLifeFromSublife (LifeMap* sublifep) {
-	// Any varrefs under a if/else branch affect statements outside and after the if/else
-	for (LifeMap::iterator it = sublifep->begin(); it!=sublifep->end(); ++it) {
-	    clearLastAssign(it->first);
-	}
-    }
-    void dualBranch (LifeMap* life1p, LifeMap* life2p) {
-	// Find any common sets on both branches of IF and propagate upwards
-	//lifeDump(life1p);
-	//lifeDump(life2p);
-	m_ifCount++;
-	for (LifeMap::iterator it = life1p->begin(); it!=life1p->end(); ++it) {
-	    // When the if branch sets a var before it's used, mark that variable
-	    if (it->second.firstSet()) it->first->user(m_ifCount);
-	}
-	for (LifeMap::iterator it = life2p->begin(); it!=life2p->end(); ++it) {
-	    // When the else branch sets a var before it's used
-	    AstVarScope* nodep = it->first;
-	    if (it->second.firstSet()
-		&& nodep->user()==m_ifCount) {	// And the if hit the same var
-		UINFO(4,"DUALBRANCH "<<nodep<<endl);
-		LifeMap::iterator iter = m_lifep->find(nodep);
-		if (iter != m_lifep->end()) {
-		    checkRemoveAssign(&(iter->second));
-		    iter->second.clearAssign();
-		} else {
-		    m_lifep->insert(make_pair(nodep,LifeVarEntry(true)));
-		}
-	    }
-	}
-	//lifeDump(m_lifep);
-    }
+};
 
+//######################################################################
+// Life state, as a visitor of each AstNode
+
+class LifeVisitor : public AstNVisitor {
+private:
+    // STATE
+    LifeState* m_statep;	// Current state
+    //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(AstModule* nodep, AstNUser*) {
-	// Only track the top scopes, not lower level functions
-	if (nodep->isTop()) nodep->iterateChildren(*this);
-    }
-    virtual void visit(AstTopScope* nodep, AstNUser*) {
-	AstNode::userClearTree();	// userp() used on entire tree
-	AstNode::user2ClearTree();	// userp() used on entire tree
-	AstNode::user3ClearTree();	// userp() used on entire tree
-	AstNode::user4ClearTree();	// userp() used on entire tree
-
-	AstScope* scopep = nodep->scopep();
-	if (!scopep) nodep->v3fatalSrc("TopScope has no scope\n");
-	AstCFunc* evalp = NULL;
-	for (AstNode* searchp = scopep->blocksp(); searchp; searchp=searchp->nextp()) {
-	    if (AstCFunc* funcp = searchp->castCFunc()) {
-		if (funcp->name() == "_eval") {
-		    evalp = funcp;
-		    break;
-		}
-	    }
-	}
-	if (!evalp) nodep->v3fatalSrc("Top _eval entry function not found\n");
-	evalp->iterateChildren(*this);
-    }
-
     virtual void visit(AstVarRef* nodep, AstNUser*) {
 	// Consumption/generation of a variable, 
 	// it's used so can't elim assignment before this use.
@@ -191,44 +281,59 @@ private:
 	//
 	AstVarScope* vscp = nodep->varScopep();
 	if (!vscp) nodep->v3fatalSrc("Scope not assigned");
-	clearLastAssign(vscp);
+	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
+	vluint64_t lastEdit = AstNode::editCountGbl();	// When it was last edited
 	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()) {
 	    AstVarScope* vscp = nodep->lhsp()->castVarRef()->varScopep();
 	    if (!vscp) vscp->v3fatalSrc("Scope lost on variable");
-	    setLast(vscp, nodep);
+	    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);
-	LifeMap* prevLifeMapp = m_lifep;
-	LifeMap* ifLifep = new LifeMap;
-	LifeMap* elseLifep = new LifeMap;
+	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);
-	m_lifep = prevLifeMapp;
 	// Find sets on both flows
-	dualBranch (ifLifep, elseLifep);
+	m_lifep->dualBranch (ifLifep, elseLifep);
 	// For the next assignments, clear any variables that were read or written in the block
-	clearLifeFromSublife(ifLifep);
-	clearLifeFromSublife(elseLifep);
+	ifLifep->lifeToAbove();
+	elseLifep->lifeToAbove();
 	delete ifLifep;
 	delete elseLifep;
     }
@@ -240,24 +345,25 @@ private:
 	// 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 in the body.
-	LifeMap* prevLifeMapp = m_lifep;
-	LifeMap* condLifep = new LifeMap;
-	LifeMap* bodyLifep = new LifeMap;
+	// 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);
-	m_lifep = prevLifeMapp;
 	// For the next assignments, clear any variables that were read or written in the block
-	clearLifeFromSublife(condLifep);
-	clearLifeFromSublife(bodyLifep);
+	condLifep->lifeToAbove();
+	bodyLifep->lifeToAbove();
 	delete condLifep;
 	delete bodyLifep;
     }
@@ -267,6 +373,7 @@ private:
 	// Enter the function and trace it
 	nodep->funcp()->accept(*this);
     }
+
     virtual void visit(AstVar*, AstNUser*) {}	// Don't want varrefs under it
     virtual void visit(AstNode* nodep, AstNUser*) {
 	nodep->iterateChildren(*this);
@@ -274,15 +381,47 @@ private:
 
 public:
     // CONSTRUCTORS
-    LifeVisitor(AstNetlist* nodep) {
-	m_ifCount = 1;
-	m_lifep = new LifeMap;
+    LifeVisitor(AstCFunc* nodep, LifeState* statep) {
+	UINFO(4,"  LifeVisitor on "<<nodep<<endl);
+	m_statep = statep;
+	{
+	    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(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);
-	delete m_lifep;
-    }
-    virtual ~LifeVisitor() {
-	V3Stats::addStat("Optimizations, Lifetime assign deletions", m_statAssnDel);
     }
+    virtual ~LifeTopVisitor() {}
 };
 
 //######################################################################
@@ -290,6 +429,6 @@ public:
 
 void V3Life::lifeAll(AstNetlist* nodep) {
     UINFO(2,__FUNCTION__<<": "<<endl);
-    // Delete lifelicate assignments
-    LifeVisitor visitor (nodep);
+    LifeState state;
+    LifeTopVisitor visitor (nodep, &state);
 }

src/V3Task.cpp

@@ -321,6 +321,7 @@ private:
 	if (rtnvarp) funcp->addArgsp(rtnvarp);
 	funcp->dontCombine(true);
 	funcp->funcPublic(true);
+	funcp->entryPoint(true);
 	funcp->isStatic(false);
 
 	// We need to get a pointer to all of our variables (may have eval'ed something else earlier)

src/Verilator.cpp

@@ -327,6 +327,7 @@ void process () {
     v3Global.rootp()->dumpTreeFile(v3Global.debugFilename("clock.tree"));
 
     // Cleanup any dly vars or other temps that are simple assignments
+    // Life must be done before Subst, as it assumes each CFunc under _eval is called only once.
     if (v3Global.opt.oLife()) {
 	V3Life::lifeAll(v3Global.rootp());
     }

test_regress/t/t_func.v

@@ -23,10 +23,9 @@ module t;
       nop(32'h11);
 
       global = 32'h00000001;
-      flipbit(global,5'd8);
-      flipbit(global,5'd16);
-      flipbit(global,5'd24);
-      if (global !== 32'h01010101) $stop;
+      flipupperbit(global,4'd4);
+      flipupperbit(global,4'd12);
+      if (global !== 32'h10100001) $stop;
 
       $write("*-* All Finished *-*\n");
       $finish;
@@ -76,10 +75,14 @@ module t;
       end
    endtask
 
-   task flipbit;
+   task flipupperbit;
       inout [31:0] vector;
-      input [4:0] bitnum;
-      vector[bitnum] = vector[bitnum] ^ 1'b1;
+      input [3:0] bitnum;
+      reg [4:0]   bitnum2;
+      begin
+	 bitnum2 = {1'b1, bitnum};	// A little math to test constant propagation
+	 vector[bitnum2] = vector[bitnum2] ^ 1'b1;
+      end
    endtask
 
 endmodule

test_regress/t/t_var_life.pl

@@ -12,7 +12,8 @@ compile (
 	 );
 
 if ($Last_Self->{v3}) {
-    file_grep ($Last_Self->{stats}, qr/Optimizations, Lifetime assign deletions\s+3/i);
+    file_grep ($Last_Self->{stats}, qr/Optimizations, Lifetime assign deletions\s+4/i);
+    file_grep ($Last_Self->{stats}, qr/Optimizations, Lifetime constant prop\s+2/i);
 }
 
 execute (