From ca4e3c173753067893e833eea8736504fcf09fef Mon Sep 17 00:00:00 2001
From: Wilson Snyder <wsnyder@wsnyder.org>
Date: Tue, 26 Sep 2006 17:05:08 +0000
Subject: [PATCH] Eliminate assigned only variables
git-svn-id: file://localhost/svn/verilator/trunk/verilator@797 77ca24e4-aefa-0310-84f0-b9a241c72d87
---
src/V3Dead.cpp | 40 +++++++++++++++++++++++++++++++++++++---
src/V3Life.cpp | 26 +++++++++++++++++++++++---
src/Verilator.cpp | 7 +++++++
3 files changed, 67 insertions(+), 6 deletions(-)
diff --git a/src/V3Dead.cpp b/src/V3Dead.cpp
index 573b16113..fb8cde3be 100644
--- a/src/V3Dead.cpp
+++ b/src/V3Dead.cpp
@@ -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);
diff --git a/src/V3Life.cpp b/src/V3Life.cpp
index d94df75fa..c35a87b1f 100644
--- a/src/V3Life.cpp
+++ b/src/V3Life.cpp
@@ -264,7 +264,8 @@ public:
class LifeVisitor : public AstNVisitor {
private:
// STATE
- LifeState* m_statep; // Current state
+ LifeState* m_statep; // Current state
+ bool m_sideEffect; // Side effects discovered in assign RHS
//static int debug() { return 9; }
// LIFE MAP
@@ -289,7 +290,9 @@ private:
}
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
@@ -297,7 +300,7 @@ private:
V3Const::constifyTree(nodep->rhsp());
}
// Has to be direct assignment without any EXTRACTing.
- if (nodep->lhsp()->castVarRef()) {
+ 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);
@@ -373,6 +376,10 @@ private:
// Enter the function and trace it
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*) {
@@ -381,9 +388,10 @@ private:
public:
// CONSTRUCTORS
- LifeVisitor(AstCFunc* nodep, LifeState* statep) {
+ 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);
@@ -409,6 +417,18 @@ private:
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
diff --git a/src/Verilator.cpp b/src/Verilator.cpp
index e132efd92..85b95e5bc 100644
--- a/src/Verilator.cpp
+++ b/src/Verilator.cpp
@@ -248,7 +248,13 @@ void process () {
V3Case::caseAll(v3Global.rootp());
v3Global.rootp()->dumpTreeFile(v3Global.debugFilename("case.tree"));
+ // Push constants across variables and remove redundant assignments
V3Const::constifyAll(v3Global.rootp());
+ if (v3Global.opt.oLife()) {
+ V3Life::lifeAll(v3Global.rootp());
+ v3Global.rootp()->dumpTreeFile(v3Global.debugFilename("life.tree"));
+ }
+
//v3Global.rootp()->dumpTreeFile(v3Global.debugFilename("const.tree"));
// Make large low-fanin logic blocks into lookup tables
@@ -329,6 +335,7 @@ void process () {
// 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()) {
+ V3Const::constifyAll(v3Global.rootp());
V3Life::lifeAll(v3Global.rootp());
}
if (v3Global.opt.oLifePost()) {