//
// For a given BasicBlock, compute which variables are used.
//
Assignments DataFlowUtil::uses(const BasicBlock& block) {
Assignments useSet;
for (BasicBlock::const_reverse_iterator it = block.rbegin(); it != block.rend(); ++it) {
const Instruction& instr = *it;
const User* user = &instr;
// iterate through all operands
User::const_op_iterator OI, OE;
for(OI = user->op_begin(), OE = user->op_end(); OI != OE; ++OI) {
Value* val = *OI;
// check if the operand is used
if ((isa<Instruction>(val) || isa<Argument>(val)) && (!isa<PHINode>(val))) {
useSet.insert(Assignment(val));
}
}
useSet.erase(Assignment(&instr));
}
return useSet;
}
//
// The following functions perform basic set operations in O(n*log(m)) time,
// where m and n are the sizes of the sets. For our purposes, this is fast
// enough.
//
// The result of these operations is stored back into the 1st argument.
//
void DataFlowUtil::setSubtract(Assignments& dest, const Assignments& src) {
for (Assignments::const_iterator i = src.begin(); i != src.end(); ++i) {
const Assignment& sub = *i;
dest.erase(sub);
}
}