/** Perform the actual copy propagation. */
public void perform() {
Stack<Chord> wl = WorkArea.<Chord>getStack("perform CP");
Chord start = scribble.getBegin();
boolean doSubscripts = scribble.scalarReplacementPerformed();
// If subscript addresses are propagated before scalar replacement
// is performed, scalar replacement generates incorrect code.
wl.push(start);
Chord.nextVisit();
start.setVisited();
while (!wl.empty()) {
Chord s = wl.pop();
s.pushOutCfgEdges(wl);
if (s.isAssignChord()) {
visitExprChord((ExprChord) s, doSubscripts);
}
}
WorkArea.<Chord>returnStack(wl);
if (rChanged) {
scribble.recomputeRefs();
}
}
/**
* Return true if this is a legal loop. A legal loop contains no function calls and has no scalar
* variable cycles. A cycle exists when the variable is referenced before it is defed. We go to
* some trouble to allow loops containing cycles such as
*
* <pre>
* s = s + a(i,j)
* </pre>
*
* to be permuted.
*/
private boolean legalLoop(LoopHeaderChord loop) {
Stack<Chord> wl = WorkArea.<Chord>getStack("legalLoop");
References refs = scribble.getRefs();
Chord.nextVisit();
wl.push(loop);
loop.setVisited();
int n = loop.numLoopExits();
for (int i = 0; i < n; i++) loop.getLoopExit(i).setVisited();
boolean legal = true;
outer:
while (!wl.empty()) {
Chord c = wl.pop();
if (c.getCall(true) != null) {
legal = false;
break;
}
if ((c instanceof DecisionChord) && (c != loop.getLoopTest())) {
legal = false;
break;
}
if (c.isAssignChord() && !c.isPhiExpr()) {
ExprChord ec = (ExprChord) c;
Expr lhs = ec.getLValue();
Expr rhs = ec.getRValue();
// The variable is both defed and used in the loop and
// we don't know how it is used. For example, it could be
// s = s + 1
// c(i,j) = s
// or
// c(i,j) = s
// s = s + 1
// We want to allow
// s = s + c(i,j)
// because we know that s is not used to specify the
// value of an array element. We want to allow
// s = ...
// = s
// since there is no cycle.
if (lhs instanceof LoadDeclAddressExpr) {
LoadDeclAddressExpr ldae = (LoadDeclAddressExpr) lhs;
VariableDecl vd = ldae.getDecl().returnVariableDecl();
if ((vd != null) && !loop.isLoopIndex(vd)) {
boolean cycle = false;
Iterator<Chord> it1 = refs.getUseChords(vd);
while (it1.hasNext()) {
Chord s = it1.next();
cycle |= (s == c);
}
Iterator<Chord> it2 = refs.getUseChords(vd);
while (it2.hasNext()) {
Chord s = it2.next();
if (c == s) continue;
if (s.getLoopHeader() != loop) continue;
if (cycle) {
// There was a cycle and another use.
// s = s + 1
// = s
legal = false;
break outer;
}
// Check for a use before the def.
while (true) {
s = s.getNextChord();
if (s == null) break;
if (s == c) {
legal = false;
break outer;
}
}
}
}
}
}
c.pushOutCfgEdges(wl);
}
WorkArea.<Chord>returnStack(wl);
return legal;
}
private void visitExprChord(ExprChord se, boolean doSubscripts) {
if (se.getPredicate() != null) {
return;
}
Expr rvalue = se.getRValue();
if (rvalue instanceof PhiExpr) {
return;
}
if (rvalue instanceof DualExpr) {
if (!doSubscripts && (((DualExpr) rvalue).getHigh() instanceof SubscriptExpr)) {
return; // Don't mess up ScalarReplacement.
}
rvalue = ((DualExpr) rvalue).getLow();
}
// Check if the statement is a simple assignment to a variable.
Expr lvalue = se.getLValue();
if (!(lvalue instanceof LoadDeclAddressExpr)) {
return;
}
if (!rvalue.getCoreType().isAtomicType()) {
return;
}
LoadDeclAddressExpr lhs = (LoadDeclAddressExpr) lvalue;
VariableDecl ldecl = (VariableDecl) lhs.getDecl();
if (ldecl.isNotAliasCandidate()) {
return;
}
if (doSubscripts) {
while (rvalue instanceof DualExpr) {
rvalue = rvalue.getLow();
}
}
Expr rv = rvalue;
while (rv.isCast()) {
rv = rv.getOperand(0);
}
if (!(rv instanceof LoadDeclValueExpr)) {
if (!(rv instanceof AdditionExpr) && !(rv instanceof SubtractionExpr)) {
return;
}
if (!rv.optimizationCandidate()) {
return;
}
BinaryExpr be = (BinaryExpr) rv;
Expr ra = be.getRightArg();
if (!ra.isLiteralExpr()) {
return;
}
if (!ra.getCoreType().isIntegerType()) {
return;
}
Expr la = be.getLeftArg();
while (la.isCast()) {
la = la.getOperand(0);
}
if (!(la instanceof LoadDeclValueExpr)) {
return; // It's not a simple add or subtract.
}
// Undo some of the damage caused by ValNum & LICM. Move simple
// adds & subtracts to reduce register pressure.
// It makes no sense to propagate an addition expression that
// references a variable that should not be aliased. For
// example, if the variable is in memory, this could increase
// the number of memory references and undo much of what global
// variable replacement tries to do.
VariableDecl org = ((VariableDecl) ((LoadDeclValueExpr) la).getDecl()).getOriginal();
if ((org == ldecl.getOriginal()) || org.isNotAliasCandidate()) {
return;
}
LoopHeaderChord lh = be.getChord().getLoopHeader();
LoadExpr[] uda = se.getDefUseArray();
for (int i = 0; i < uda.length; i++) {
LoadExpr ud = uda[i];
Chord s = ud.getChord();
LoopHeaderChord slh = s.getLoopHeader();
Note out = ud.getOutDataEdge();
// Propagate the expression.
out.changeInDataEdge(ud, rvalue.copy());
ud.unlinkExpression();
rChanged = true;
}
return;
}
LoadDeclValueExpr rhs = (LoadDeclValueExpr) rv;
VariableDecl rdecl = (VariableDecl) rhs.getDecl();
if (!rdecl.optimizationCandidate()) {
return;
}
if ((rdecl == rdecl.getOriginal()) && (ldecl.getOriginal() == rdecl)) {
return; // The original variable is special in SSA form.
}
ExprChord rhsud = rhs.getUseDef();
if (!doSubscripts && (rhsud != null)) {
// Don't mess up scalar replacement by creating new data
// dependence edges.
Expr rhsv = rhsud.getRValue();
if (rhsv instanceof DualExpr) {
return;
}
}
// For now if the may use info is not null, do not propagate.
if (rhs.getMayUse() != null) {
return;
}
MayDef md = se.getMayDef();
LoadExpr[] uses = se.getDefUseArray();
for (int i = 0; i < uses.length; i++) {
LoadExpr use = uses[i];
// Copy propagation of a variable into a phi function just
// results in extra copy operations. For example, consider
// x1 = y
// l: x3 = phi(x1, x4)
//
// After copy propagation
// x1 = y
// l: x3 = phi(y, x4)
//
// After phi removal
// x1 = y
// x3 = y
// l:
//
// After variable coalescing
// x = y
// x = y
if (use.getOutDataEdge() instanceof PhiExpr) {
continue;
}
boolean doit = true;
// If there is may def information associated with the
// lhs of the expression, check to see if it can be
// propagated.
if (!unsafe) {
MayUse mu = use.getMayUse();
if (md != null) {
if (mu == null) {
doit = false;
} else {
Declaration d1 = null;
MayDef ud = mu.findMayDef();
if (ud != null) {
d1 = ((LoadExpr) (ud.getLhs())).getDecl();
}
/*Declaration d1 = mu.getDecl();*/
Declaration d2 = ((LoadExpr) md.getLhs()).getDecl();
doit = (d1 == d2);
}
}
}
if (doit) { // Change the variable in the use.
if (rv == rvalue) {
use.setDecl(rdecl);
use.setUseDef(rhsud);
} else {
Note out = use.getOutDataEdge();
out.changeInDataEdge(use, rvalue.copy());
use.unlinkExpression();
}
rChanged = true;
propagationCount++;
} else {
aliasInhibitedCount++;
}
}
}
