// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
void SimpleDeadCodeElimination::RemoveDeadVariables(Function* function) {
SparseBitVector liveVars;
// Scan every instruction in the function and mark any local variable
// that appears as an operand. All variables that are not marked are deleted.
function->ForEachInstruction([&liveVars](Instruction* instr) -> bool {
for(int i = 0; i < instr->SourceOpCount(); i++) {
if(auto variableRef = instr->GetSourceOp(i)->As<VariableReference>()) {
auto variable = variableRef->GetVariable(); // Only local variables.
if(variable && (variable->IsParameter() == false)) {
liveVars.SetBit(variable->Id());
}
}
}
return true;
});
// Now removed all unused variables.
for(int i = 0; i < function->VariableCount(); i++) {
auto variable = function->Variables()[i];
if(liveVars.IsSet(variable->Id()) == false) {
function->RemoveVariable(variable);
i--;
}
}
}
const TBlock* GetStartBlock(const TFunction* function) {
// It's possible that the function has multiple exit blocks.
// In this case we need to create a fake block that acts like an
// "unique" exit block, whose predecessors are the real exit blocks.
if(exitBlock_) {
// A fake exit block has been already created.
return exitBlock_;
}
StaticList<const TBlock*, 16> exitBlocks;
const TBlock* block = function->FirstBlock();
while(block) {
if(block->SuccessorCount() == 0) {
// This is an exit block.
exitBlocks.Add(block);
returnBlocks_.SetBit(block->Id());
}
block = block->NextBlock();
}
// Now return the exit block. If there is no unique block
// we create a "fake" one that has all the exit blocks
// as its predecessors. This block will be deleted after the analysis.
if(exitBlocks.Count() == 1) {
// There is a single exit block.
return exitBlocks[0];
}
else if(exitBlocks.Count() > 1) {
// There are multiple exit blocks, create a fake block.
exitBlock_ = TBlock::GetBlock("#fakeBlock");
for(int i = 0; i < exitBlocks.Count(); i++) {
exitBlock_->AddPredecessor(const_cast<TBlock*>(exitBlocks[i]));
}
return exitBlock_;
}
else {
// There is no exit block. This can happen, for example, if the last
// block represents an infinite loop. In this case return the last block.
return function->LastBlock();
}
}
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
void AggregateCopyPropagation::IterateToFixedpoint() {
// We use an iterative data-flow algorithm to propagate the copies
// that are available on entry of each block. Add the blocks
// in reverse-postorder, this minimizes the number of iterations.
StaticList<Block*, 64> worklist;
SparseBitVector inWorklist;
CFGInfo<Block, Function> cfgInfo(funct_->FirstBlock(), false);
auto& postorderList = cfgInfo.PostorderList();
int copyCount = infoList_.Count();
// Add all blocks to the worklist.
for(int i = 0; i < postorderList.Count(); i++) {
auto block = const_cast<Block*>(postorderList[i]);
worklist.Add(block);
inWorklist.SetBit(block->Id());
}
while(worklist.IsNotEmpty()) {
// Extract a block from the worklist.
auto block = worklist.RemoveLast();
inWorklist.ResetBit(block->Id());
// Compute the 'in' set, which is the intersection
// out the 'out' sets of the predecessors.
BitVector inSet(copyCount, false);
auto predecessorEnum = block->GetPredecessorEnum();
bool first = true;
while(predecessorEnum.IsValid()) {
auto predecessorBlock = predecessorEnum.Next();
if(first) {
inSet = outSets_[predecessorBlock];
first = false;
}
else inSet.And(outSets_[predecessorBlock]);
}
// Save the 'in' set, it's needed later
// when we want to eliminate the copies.
inSets_.Add(block, inSet);
// Now compute the new 'out' set, which is the union of the 'copy' set
// with the 'in' set, from which the 'kill' set has been subtracted.
// Out(B) = Copy(B) U (In(B) - Kill(B))
BitVector outSet = copySets_[block];
inSet.Difference(killSets_[block]);
outSet.Or(inSet);
if(outSets_[block] != outSet) {
// The 'out' set must be updated, and all successors
// must be added to the worklist and reprocessed.
outSets_[block] = outSet;
auto successorEnum = block->GetSuccessorEnum();
while(successorEnum.IsValid()) {
auto successorBlock = successorEnum.Next();
if(inWorklist.IsSet(successorBlock->Id()) == false) {
worklist.Add(successorBlock);
inWorklist.IsSet(successorBlock->Id());
}
}
}
}
}