// Helper function for UserProc::propagateStatements()
// Works on basic block n; call from UserProc with n=0 (entry BB)
// If an SSA location is in usedByDomPhi it means it is used in a phi that dominates its assignment
// However, it could turn out that the phi is dead, in which case we don't want to keep the associated entries in
// usedByDomPhi. So we maintain the map defdByPhi which maps locations defined at a phi to the phi statements. Every
// time we see a use of a location in defdByPhi, we remove that map entry. At the end of the procedure we therefore have
// only dead phi statements in the map, so we can delete the associated entries in defdByPhi and also remove the dead
// phi statements.
// We add to the set usedByDomPhi0 whenever we see a location referenced by a phi parameter. When we see a definition
// for such a location, we remove it from the usedByDomPhi0 set (to save memory) and add it to the usedByDomPhi set.
// For locations defined before they are used in a phi parameter, there will be no entry in usedByDomPhi, so we ignore
// it. Remember that each location is defined only once, so that's the time to decide if it is dominated by a phi use or
// not.
void DataFlow::findLiveAtDomPhi(int n, LocationSet& usedByDomPhi, LocationSet& usedByDomPhi0,
std::map<Exp*, PhiAssign*, lessExpStar>& defdByPhi) {
// For each statement this BB
BasicBlock::rtlit rit; StatementList::iterator sit;
PBB bb = BBs[n];
Statement* S;
for (S = bb->getFirstStmt(rit, sit); S; S = bb->getNextStmt(rit, sit)) {
if (S->isPhi()) {
// For each phi parameter, insert an entry into usedByDomPhi0
PhiAssign* pa = (PhiAssign*)S;
PhiAssign::iterator it;
for (it = pa->begin(); it != pa->end(); ++it) {
if (it->e) {
RefExp* re = new RefExp(it->e, it->def);
usedByDomPhi0.insert(re);
}
}
// Insert an entry into the defdByPhi map
RefExp* wrappedLhs = new RefExp(pa->getLeft(), pa);
defdByPhi[wrappedLhs] = pa;
// Fall through to the below, because phi uses are also legitimate uses
}
LocationSet ls;
S->addUsedLocs(ls);
// Consider uses of this statement
LocationSet::iterator it;
for (it = ls.begin(); it != ls.end(); ++it) {
// Remove this entry from the map, since it is not unused
defdByPhi.erase(*it);
}
// Now process any definitions
ls.clear();
S->getDefinitions(ls);
for (it = ls.begin(); it != ls.end(); ++it) {
RefExp* wrappedDef = new RefExp(*it, S);
// If this definition is in the usedByDomPhi0 set, then it is in fact dominated by a phi use, so move it to
// the final usedByDomPhi set
if (usedByDomPhi0.find(wrappedDef) != usedByDomPhi0.end()) {
usedByDomPhi0.remove(wrappedDef);
usedByDomPhi.insert(wrappedDef);
}
}
}
// Visit each child in the dominator graph
// Note: this is a linear search!
// Note also that usedByDomPhi0 may have some irrelevant entries, but this will do no harm, and attempting to erase
// the irrelevant ones would probably cost more than leaving them alone
int sz = idom.size();
for (int c = 0; c < sz; ++c) {
if (idom[c] != n) continue;
// Recurse to the child
findLiveAtDomPhi(c, usedByDomPhi, usedByDomPhi0, defdByPhi);
}
}
bool DataFlow::renameBlockVars(UserProc* proc, int n, bool clearStacks /* = false */ ) {
if (++progress > 200) {
std::cerr << 'r' << std::flush;
progress = 0;
}
bool changed = false;
// Need to clear the Stacks of old, renamed locations like m[esp-4] (these will be deleted, and will cause compare
// failures in the Stacks, so it can't be correctly ordered and hence balanced etc, and will lead to segfaults)
if (clearStacks) Stacks.clear();
// For each statement S in block n
BasicBlock::rtlit rit; StatementList::iterator sit;
PBB bb = BBs[n];
Statement* S;
for (S = bb->getFirstStmt(rit, sit); S; S = bb->getNextStmt(rit, sit)) {
// if S is not a phi function (per Appel)
/* if (!S->isPhi()) */ {
// For each use of some variable x in S (not just assignments)
LocationSet locs;
if (S->isPhi()) {
PhiAssign* pa = (PhiAssign*)S;
Exp* phiLeft = pa->getLeft();
if (phiLeft->isMemOf() || phiLeft->isRegOf())
phiLeft->getSubExp1()->addUsedLocs(locs);
// A phi statement may use a location defined in a childless call, in which case its use collector
// needs updating
PhiAssign::iterator pp;
for (pp = pa->begin(); pp != pa->end(); ++pp) {
Statement* def = pp->def;
if (def && def->isCall())
((CallStatement*)def)->useBeforeDefine(phiLeft->clone());
}
}
else { // Not a phi assignment
S->addUsedLocs(locs);
}
LocationSet::iterator xx;
for (xx = locs.begin(); xx != locs.end(); xx++) {
Exp* x = *xx;
// Don't rename memOfs that are not renamable according to the current policy
if (!canRename(x, proc)) continue;
Statement* def = NULL;
if (x->isSubscript()) { // Already subscripted?
// No renaming required, but redo the usage analysis, in case this is a new return, and also because
// we may have just removed all call livenesses
// Update use information in calls, and in the proc (for parameters)
Exp* base = ((RefExp*)x)->getSubExp1();
def = ((RefExp*)x)->getDef();
if (def && def->isCall()) {
// Calls have UseCollectors for locations that are used before definition at the call
((CallStatement*)def)->useBeforeDefine(base->clone());
continue;
}
// Update use collector in the proc (for parameters)
if (def == NULL)
proc->useBeforeDefine(base->clone());
continue; // Don't re-rename the renamed variable
}
// Else x is not subscripted yet
if (STACKS_EMPTY(x)) {
if (!Stacks[defineAll].empty())
def = Stacks[defineAll].top();
else {
// If the both stacks are empty, use a NULL definition. This will be changed into a pointer
// to an implicit definition at the start of type analysis, but not until all the m[...]
// have stopped changing their expressions (complicates implicit assignments considerably).
def = NULL;
// Update the collector at the start of the UserProc
proc->useBeforeDefine(x->clone());
}
}
else
def = Stacks[x].top();
if (def && def->isCall())
// Calls have UseCollectors for locations that are used before definition at the call
((CallStatement*)def)->useBeforeDefine(x->clone());
// Replace the use of x with x{def} in S
changed = true;
if (S->isPhi()) {
Exp* phiLeft = ((PhiAssign*)S)->getLeft();
phiLeft->setSubExp1(phiLeft->getSubExp1()->expSubscriptVar(x, def /*, this*/));
} else {
S->subscriptVar(x, def /*, this */);
}
}
}
// MVE: Check for Call and Return Statements; these have DefCollector objects that need to be updated
// Do before the below, so CallStatements have not yet processed their defines
if (S->isCall() || S->isReturn()) {
DefCollector* col;
if (S->isCall())
col = ((CallStatement*)S)->getDefCollector();
else
col = ((ReturnStatement*)S)->getCollector();
col->updateDefs(Stacks, proc);
}
// For each definition of some variable a in S
LocationSet defs;
S->getDefinitions(defs);
LocationSet::iterator dd;
for (dd = defs.begin(); dd != defs.end(); dd++) {
Exp* a = *dd;
// Don't consider a if it cannot be renamed
bool suitable = canRename(a, proc);
if (suitable) {
// Push i onto Stacks[a]
// Note: we clone a because otherwise it could be an expression that gets deleted through various
// modifications. This is necessary because we do several passes of this algorithm to sort out the
// memory expressions
Stacks[a->clone()].push(S);
// Replace definition of a with definition of a_i in S (we don't do this)
}
// FIXME: MVE: do we need this awful hack?
if (a->getOper() == opLocal) {
Exp *a1 = S->getProc()->expFromSymbol(((Const*)a->getSubExp1())->getStr());
assert(a1);
a = a1;
// Stacks already has a definition for a (as just the bare local)
if (suitable) {
Stacks[a->clone()].push(S);
}
}
}
// Special processing for define-alls (presently, only childless calls).
// But note that only everythings at the current memory level are defined!
if (S->isCall() && ((CallStatement*)S)->isChildless() && !Boomerang::get()->assumeABI) {
// S is a childless call (and we're not assuming ABI compliance)
Stacks[defineAll]; // Ensure that there is an entry for defineAll
std::map<Exp*, std::stack<Statement*>, lessExpStar>::iterator dd;
for (dd = Stacks.begin(); dd != Stacks.end(); ++dd) {
// if (dd->first->isMemDepth(memDepth))
dd->second.push(S); // Add a definition for all vars
}
}
}
// For each successor Y of block n
std::vector<PBB>& outEdges = bb->getOutEdges();
unsigned numSucc = outEdges.size();
for (unsigned succ = 0; succ < numSucc; succ++) {
PBB Ybb = outEdges[succ];
// Suppose n is the jth predecessor of Y
int j = Ybb->whichPred(bb);
// For each phi-function in Y
Statement* S;
for (S = Ybb->getFirstStmt(rit, sit); S; S = Ybb->getNextStmt(rit, sit)) {
PhiAssign* pa = dynamic_cast<PhiAssign*>(S);
// if S is not a phi function, then quit the loop (no more phi's)
// Wrong: do not quit the loop: there's an optimisation that turns a PhiAssign into an ordinary Assign.
// So continue, not break.
if (!pa) continue;
// Suppose the jth operand of the phi is a
// For now, just get the LHS
Exp* a = pa->getLeft();
// Only consider variables that can be renamed
if (!canRename(a, proc)) continue;
Statement* def;
if (STACKS_EMPTY(a))
def = NULL; // No reaching definition
else
def = Stacks[a].top();
// "Replace jth operand with a_i"
pa->putAt(j, def, a);
}
}
// For each child X of n
// Note: linear search!
unsigned numBB = proc->getCFG()->getNumBBs();
for (unsigned X=0; X < numBB; X++) {
if (idom[X] == n)
renameBlockVars(proc, X);
}
// For each statement S in block n
// NOTE: Because of the need to pop childless calls from the Stacks, it is important in my algorithm to process the
// statments in the BB *backwards*. (It is not important in Appel's algorithm, since he always pushes a definition
// for every variable defined on the Stacks).
BasicBlock::rtlrit rrit; StatementList::reverse_iterator srit;
for (S = bb->getLastStmt(rrit, srit); S; S = bb->getPrevStmt(rrit, srit)) {
// For each definition of some variable a in S
LocationSet defs;
S->getDefinitions(defs);
LocationSet::iterator dd;
for (dd = defs.begin(); dd != defs.end(); dd++) {
if (canRename(*dd, proc)) {
// if ((*dd)->getMemDepth() == memDepth)
std::map<Exp*, std::stack<Statement*>, lessExpStar>::iterator ss = Stacks.find(*dd);
if (ss == Stacks.end()) {
std::cerr << "Tried to pop " << *dd << " from Stacks; does not exist\n";
assert(0);
}
ss->second.pop();
}
}
// Pop all defs due to childless calls
if (S->isCall() && ((CallStatement*)S)->isChildless()) {
std::map<Exp*, std::stack<Statement*>, lessExpStar>::iterator sss;
for (sss = Stacks.begin(); sss != Stacks.end(); ++sss) {
if (!sss->second.empty() && sss->second.top() == S) {
sss->second.pop();
}
}
}
}
return changed;
}
