/**
* @brief Finds a next SCC and its represent and returns them.
*
* @param[in] sccs All SCCs in the call graph.
* @param[in] computedFuncs Functions that already have been included in
* FuncInfoCompOrder::order.
* @param[in] remainingFuncs Functions that haven't been included in
* FuncInfoCompOrder::order.
*
* @par Preconditions
* - @a remainingFuncs is non-empty
* - @a remainingFuncs doesn't contain a function which calls just functions
* from @a computedFuncs.
*/
CallInfoObtainer::SCCWithRepresent CallInfoObtainer::findNextSCC(const FuncSetSet &sccs,
const FuncSet &computedFuncs, const FuncSet &remainingFuncs) const {
PRECONDITION(!remainingFuncs.empty(), "it should not be empty");
//
// We try to locate an SCC whose members call just the functions in
// the SCC or in computedFuncs. Then, if the found SCC contains a function
// from remainingFuncs, return the function.
//
// For every SCC...
for (const auto &scc : sccs) {
bool sccFound = true;
ShPtr<Function> funcFromRemainingFuncs;
// For every function in the SCC...
for (const auto &func : scc) {
// Check whether the function calls just the functions in the SCC
// or in computedFuncs.
ShPtr<CG::CalledFuncs> calledFuncs(cg->getCalledFuncs(func));
FuncSet mayCall(setUnion(scc, computedFuncs));
if (!setDifference(calledFuncs->callees, mayCall).empty()) {
sccFound = false;
} else {
// Have we encountered a function from remainingFuncs?
if (hasItem(remainingFuncs, func)) {
funcFromRemainingFuncs = func;
}
}
}
if (sccFound && funcFromRemainingFuncs) {
return SCCWithRepresent(scc, funcFromRemainingFuncs);
}
}
// TODO Can this happen?
printWarningMessage("[SCCComputer] No viable SCC has been found.");
FuncSet scc;
ShPtr<Function> func(*(remainingFuncs.begin()));
scc.insert(func);
return SCCWithRepresent(scc, func);
}
//
// Method: calculateGraphs()
//
// Description:
// Perform recursive bottom-up inlining of DSGraphs from callee to caller.
//
// Inputs:
// F - The function which should have its callees' DSGraphs merged into its
// own DSGraph.
// Stack - The stack used for Tarjan's SCC-finding algorithm.
// NextID - The nextID value used for Tarjan's SCC-finding algorithm.
// ValMap - The map used for Tarjan's SCC-finding algorithm.
//
// Return value:
//
unsigned
BUDataStructures::calculateGraphs (const Function *F,
TarjanStack & Stack,
unsigned & NextID,
TarjanMap & ValMap) {
assert(!ValMap.count(F) && "Shouldn't revisit functions!");
unsigned Min = NextID++, MyID = Min;
ValMap[F] = Min;
Stack.push_back(F);
//
// FIXME: This test should be generalized to be any function that we have
// already processed in the case when there isn't a main() or there are
// unreachable functions!
//
if (F->isDeclaration()) { // sprintf, fprintf, sscanf, etc...
// No callees!
Stack.pop_back();
ValMap[F] = ~0;
return Min;
}
//
// Get the DSGraph of the current function. Make one if one doesn't exist.
//
DSGraph* Graph = getOrCreateGraph(F);
//
// Find all callee functions. Use the DSGraph for this (do not use the call
// graph (DSCallgraph) as we're still in the process of constructing it).
//
FuncSet CalleeFunctions;
getAllAuxCallees(Graph, CalleeFunctions);
//
// Iterate through each call target (these are the edges out of the current
// node (i.e., the current function) in Tarjan graph parlance). Find the
// minimum assigned ID.
//
for (FuncSet::iterator I = CalleeFunctions.begin(), E = CalleeFunctions.end();
I != E; ++I) {
const Function *Callee = *I;
unsigned M;
//
// If we have not visited this callee before, visit it now (this is the
// post-order component of the Bottom-Up algorithm). Otherwise, look up
// the assigned ID value from the Tarjan Value Map.
//
TarjanMap::iterator It = ValMap.find(Callee);
if (It == ValMap.end()) // No, visit it now.
M = calculateGraphs(Callee, Stack, NextID, ValMap);
else // Yes, get it's number.
M = It->second;
//
// If we've found a function with a smaller ID than this funtion, record
// that ID as the minimum ID.
//
if (M < Min) Min = M;
}
assert(ValMap[F] == MyID && "SCC construction assumption wrong!");
//
// If the minimum ID found is not this function's ID, then this function is
// part of a larger SCC.
//
if (Min != MyID)
return Min;
//
// If this is a new SCC, process it now.
//
if (Stack.back() == F) { // Special case the single "SCC" case here.
DEBUG(errs() << "Visiting single node SCC #: " << MyID << " fn: "
<< F->getName() << "\n");
Stack.pop_back();
DEBUG(errs() << " [BU] Calculating graph for: " << F->getName()<< "\n");
DSGraph* G = getOrCreateGraph(F);
calculateGraph(G);
DEBUG(errs() << " [BU] Done inlining: " << F->getName() << " ["
<< G->getGraphSize() << "+" << G->getAuxFunctionCalls().size()
<< "]\n");
if (MaxSCC < 1) MaxSCC = 1;
//
// Should we revisit the graph? Only do it if there are now new resolvable
// callees.
FuncSet NewCallees;
getAllAuxCallees(G, NewCallees);
if (!NewCallees.empty()) {
if (hasNewCallees(NewCallees, CalleeFunctions)) {
DEBUG(errs() << "Recalculating " << F->getName() << " due to new knowledge\n");
ValMap.erase(F);
++NumRecalculations;
return calculateGraphs(F, Stack, NextID, ValMap);
}
++NumRecalculationsSkipped;
}
ValMap[F] = ~0U;
return MyID;
} else {
unsigned SCCSize = 1;
const Function *NF = Stack.back();
if(NF != F)
ValMap[NF] = ~0U;
DSGraph* SCCGraph = getDSGraph(*NF);
//
// First thing first: collapse all of the DSGraphs into a single graph for
// the entire SCC. Splice all of the graphs into one and discard all of
// the old graphs.
//
while (NF != F) {
Stack.pop_back();
NF = Stack.back();
if(NF != F)
ValMap[NF] = ~0U;
DSGraph* NFG = getDSGraph(*NF);
if (NFG != SCCGraph) {
// Update the Function -> DSG map.
for (DSGraph::retnodes_iterator I = NFG->retnodes_begin(),
E = NFG->retnodes_end(); I != E; ++I)
setDSGraph(*I->first, SCCGraph);
SCCGraph->spliceFrom(NFG);
delete NFG;
++SCCSize;
}
}
Stack.pop_back();
DEBUG(errs() << "Calculating graph for SCC #: " << MyID << " of size: "
<< SCCSize << "\n");
// Compute the Max SCC Size.
if (MaxSCC < SCCSize)
MaxSCC = SCCSize;
// Clean up the graph before we start inlining a bunch again...
SCCGraph->removeDeadNodes(DSGraph::KeepUnreachableGlobals);
// Now that we have one big happy family, resolve all of the call sites in
// the graph...
calculateGraph(SCCGraph);
DEBUG(errs() << " [BU] Done inlining SCC [" << SCCGraph->getGraphSize()
<< "+" << SCCGraph->getAuxFunctionCalls().size() << "]\n"
<< "DONE with SCC #: " << MyID << "\n");
FuncSet NewCallees;
getAllAuxCallees(SCCGraph, NewCallees);
if (!NewCallees.empty()) {
if (hasNewCallees(NewCallees, CalleeFunctions)) {
DEBUG(errs() << "Recalculating SCC Graph " << F->getName() << " due to new knowledge\n");
ValMap.erase(F);
++NumRecalculations;
return calculateGraphs(F, Stack, NextID, ValMap);
}
++NumRecalculationsSkipped;
}
ValMap[F] = ~0U;
return MyID;
}
}