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Eliminate assigned only variables

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git-svn-id: file://localhost/svn/verilator/trunk/verilator@797 77ca24e4-aefa-0310-84f0-b9a241c72d87
This commit is contained in:
Wilson Snyder
2006-09-26 17:05:08 +00:00
parent ba7b4f261a
commit ca4e3c1737
3 changed files with 67 additions and 6 deletions
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src/V3Dead.cpp
+37 -3
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@@ -29,6 +29,7 @@
#include <stdarg.h>
#include <unistd.h>
#include <vector>
#include <map>
#include "V3Global.h"
#include "V3Dead.h"
@@ -70,10 +71,15 @@ private:
// AstVar::user() -> int. Count of number of references
// AstVarScope::user() -> int. Count of number of references
// TYPES
typedef multimap<AstVarScope*,AstNodeAssign*> AssignMap;
// STATE
vector<AstVar*> m_varsp; // List of all encountered to avoid another loop through tree
vector<AstVarScope*> m_vscsp; // List of all encountered to avoid another loop through tree
AssignMap m_assignMap; // List of all simple assignments for each variable
bool m_elimUserVars; // Allow removal of user's vars
bool m_sideEffect; // Side effects discovered in assign RHS
//int debug() { return 9; }
// METHODS
@@ -102,6 +108,25 @@ private:
m_varsp.push_back(nodep);
}
virtual void visit(AstNodeAssign* nodep, AstNUser*) {
// See if simple assignments to variables may be eliminated because that variable is never used.
// Similar code in V3Life
m_sideEffect = false;
nodep->rhsp()->iterateAndNext(*this);
// Has to be direct assignment without any EXTRACTing.
AstVarRef* varrefp = nodep->lhsp()->castVarRef();
if (varrefp && !m_sideEffect
&& varrefp->varScopep()) { // For simplicity, we only remove post-scoping
m_assignMap.insert(make_pair(varrefp->varScopep(), nodep));
} else { // Track like any other statement
nodep->lhsp()->iterateAndNext(*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(AstNode* nodep, AstNUser*) {
nodep->iterateChildren(*this);
@@ -131,14 +156,22 @@ private:
}
bool canElim(AstVar* nodep) {
return (!nodep->isSigPublic() // Can't elim publics!
&& !nodep->isIO()
&& (nodep->isTemp() || nodep->isParam() || m_elimUserVars));
}
void deadCheckVar() {
// Delete any unused varscopes
for (vector<AstVarScope*>::iterator it = m_vscsp.begin(); it!=m_vscsp.end(); ++it) {
if ((*it)->user() == 0 && canElim((*it)->varp())) {
UINFO(4," Dead "<<(*it)<<endl);
(*it)->unlinkFrBack()->deleteTree(); (*it)=NULL;
AstVarScope* vscp = *it;
if (vscp->user() == 0 && canElim(vscp->varp())) {
UINFO(4," Dead "<<vscp<<endl);
pair <AssignMap::iterator,AssignMap::iterator> eqrange = m_assignMap.equal_range(vscp);
for (AssignMap::iterator it = eqrange.first; it != eqrange.second; ++it) {
AstNodeAssign* assp = it->second;
UINFO(4," Dead assign "<<assp<<endl);
assp->unlinkFrBack()->deleteTree(); assp=NULL;
}
vscp->unlinkFrBack()->deleteTree(); vscp=NULL;
}
}
for (vector<AstVar*>::iterator it = m_varsp.begin(); it!=m_varsp.end(); ++it) {
@@ -153,6 +186,7 @@ public:
// CONSTRUCTORS
DeadVisitor(AstNetlist* nodep, bool elimUserVars) {
m_elimUserVars = elimUserVars;
m_sideEffect = false;
// Operate on whole netlist
AstNode::userClearTree(); // userp() used on entire tree
nodep->accept(*this);