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Implement CFGSimplify/PhiBlockMerge*.ll 

llvm-svn: 5702
This commit is contained in:
Chris Lattner 2003-03-05 21:36:33 +00:00
parent 9115973f47
commit e54d214fcb
1 changed files with 36 additions and 10 deletions
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46
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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@ -39,8 +39,8 @@ static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) { if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
// Loop over all of the PHI nodes checking to see if there are // Loop over all of the PHI nodes checking to see if there are
// incompatible values coming in. // incompatible values coming in.
BasicBlock::iterator BBI = Succ->begin(); for (BasicBlock::iterator I = Succ->begin();
while (PHINode *PN = dyn_cast<PHINode>(&*BBI++)) { PHINode *PN = dyn_cast<PHINode>(&*I); ++I) {
// Loop up the entries in the PHI node for BB and for *PI if the values // Loop up the entries in the PHI node for BB and for *PI if the values
// coming in are non-equal, we cannot merge these two blocks (instead we // coming in are non-equal, we cannot merge these two blocks (instead we
// should insert a conditional move or something, then merge the // should insert a conditional move or something, then merge the
@ -60,10 +60,19 @@ static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
Value *OldVal = PN->removeIncomingValue(BB, false); Value *OldVal = PN->removeIncomingValue(BB, false);
assert(OldVal && "No entry in PHI for Pred BB!"); assert(OldVal && "No entry in PHI for Pred BB!");
for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(), // If this incoming value is one of the PHI nodes in BB...
End = BBPreds.end(); PredI != End; ++PredI) { if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
// Add an incoming value for each of the new incoming values... PHINode *OldValPN = cast<PHINode>(OldVal);
PN->addIncoming(OldVal, *PredI); for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
End = BBPreds.end(); PredI != End; ++PredI) {
PN->addIncoming(OldValPN->getIncomingValueForBlock(*PredI), *PredI);
}
} else {
for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
End = BBPreds.end(); PredI != End; ++PredI) {
// Add an incoming value for each of the new incoming values...
PN->addIncoming(OldVal, *PredI);
}
} }
} }
return false; return false;
@ -84,7 +93,6 @@ bool SimplifyCFG(BasicBlock *BB) {
assert(BB->getTerminator() && "Degenerate basic block encountered!"); assert(BB->getTerminator() && "Degenerate basic block encountered!");
assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!"); assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!");
// Remove basic blocks that have no predecessors... which are unreachable. // Remove basic blocks that have no predecessors... which are unreachable.
if (pred_begin(BB) == pred_end(BB) && if (pred_begin(BB) == pred_end(BB) &&
!BB->hasConstantReferences()) { !BB->hasConstantReferences()) {
@ -113,11 +121,16 @@ bool SimplifyCFG(BasicBlock *BB) {
return true; return true;
} }
// Check to see if this block has no instructions and only a single // Check to see if this block has no non-phi instructions and only a single
// successor. If so, replace block references with successor. // successor. If so, replace references to this basic block with references
// to the successor.
succ_iterator SI(succ_begin(BB)); succ_iterator SI(succ_begin(BB));
if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ? if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ?
if (BB->front().isTerminator()) { // Terminator is the only instruction!
BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
while (isa<PHINode>(*BBI)) ++BBI;
if (BBI->isTerminator()) { // Terminator is the only non-phi instruction!
BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor
if (Succ != BB) { // Arg, don't hurt infinite loops! if (Succ != BB) { // Arg, don't hurt infinite loops!
@ -131,6 +144,19 @@ bool SimplifyCFG(BasicBlock *BB) {
BB->replaceAllUsesWith(Succ); BB->replaceAllUsesWith(Succ);
std::string OldName = BB->getName(); std::string OldName = BB->getName();
// Move all PHI nodes in BB to Succ if they are alive, otherwise
// delete them.
while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
if (PN->use_empty())
BB->getInstList().erase(BB->begin()); // Nuke instruction...
else {
// The instruction is alive, so this means that Succ must have
// *ONLY* had BB as a predecessor, and the PHI node is still valid
// now. Simply move it into Succ.
BB->getInstList().remove(BB->begin());
Succ->getInstList().push_front(PN);
}
// Delete the old basic block... // Delete the old basic block...
M->getBasicBlockList().erase(BB); M->getBasicBlockList().erase(BB);