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Do not mark obviously unreachable blocks live when processing PHI nodes,

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and handle incomplete control dependences correctly.  This fixes:

Regression/Transforms/ADCE/dead-phi-edge.ll
  -> a missed optimization

Regression/Transforms/ADCE/dead-phi-edge.ll
  -> a compiler crash distilled from QT4


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20227 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-02-17 19:28:49 +00:00
parent ae02b723bf
commit 1a84bd38ef
1 changed files with 62 additions and 41 deletions
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103
lib/Transforms/Scalar/ADCE.cpp
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@ -253,7 +253,7 @@ bool ADCE::doADCE() {
// function which unwinds, exits or has side-effects, we don't want to delete
// the infinite loop or those blocks leading up to it.
for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I)
if (DT[I] == 0)
if (DT[I] == 0 && ReachableBBs.count(I))
for (pred_iterator PI = pred_begin(I), E = pred_end(I); PI != E; ++PI)
markInstructionLive((*PI)->getTerminator());
@ -281,17 +281,28 @@ bool ADCE::doADCE() {
// defined in the predecessor nodes of this block, meaning that the PHI
// makes the predecessors alive.
//
if (PHINode *PN = dyn_cast<PHINode>(I))
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (AliveBlocks.insert(PN->getIncomingBlock(i)).second)
markBlockAlive(PN->getIncomingBlock(i)); // Block is newly ALIVE!
// Loop over all of the operands of the live instruction, making sure that
// they are known to be alive as well.
//
for (unsigned op = 0, End = I->getNumOperands(); op != End; ++op)
if (Instruction *Operand = dyn_cast<Instruction>(I->getOperand(op)))
markInstructionLive(Operand);
if (PHINode *PN = dyn_cast<PHINode>(I)) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
// If the incoming edge is clearly dead, it won't have control
// dependence information. Do not mark it live.
BasicBlock *PredBB = PN->getIncomingBlock(i);
if (ReachableBBs.count(PredBB)) {
// FIXME: This should mark the control dependent edge as live, not
// necessarily the predecessor itself!
if (AliveBlocks.insert(PredBB).second)
markBlockAlive(PN->getIncomingBlock(i)); // Block is newly ALIVE!
if (Instruction *Op = dyn_cast<Instruction>(PN->getIncomingValue(i)))
markInstructionLive(Op);
}
}
} else {
// Loop over all of the operands of the live instruction, making sure that
// they are known to be alive as well.
//
for (unsigned op = 0, End = I->getNumOperands(); op != End; ++op)
if (Instruction *Operand = dyn_cast<Instruction>(I->getOperand(op)))
markInstructionLive(Operand);
}
}
DEBUG(
@ -359,7 +370,7 @@ bool ADCE::doADCE() {
// Loop over all of the successors, looking for ones that are not alive.
// We cannot save the number of successors in the terminator instruction
// here because we may remove them if we don't have a postdominator...
// here because we may remove them if we don't have a postdominator.
//
for (unsigned i = 0; i != TI->getNumSuccessors(); ++i)
if (!AliveBlocks.count(TI->getSuccessor(i))) {
@ -368,39 +379,49 @@ bool ADCE::doADCE() {
// dead...
//
PostDominatorTree::Node *LastNode = DT[TI->getSuccessor(i)];
PostDominatorTree::Node *NextNode = 0;
// There is a special case here... if there IS no post-dominator for
// the block we have no owhere to point our branch to. Instead,
// convert it to a return. This can only happen if the code branched
// into an infinite loop. Note that this may not be desirable,
// because we _are_ altering the behavior of the code. This is a well
// known drawback of ADCE, so in the future if we choose to revisit
// the decision, this is where it should be.
//
if (LastNode == 0) { // No postdominator!
// Call RemoveSuccessor to transmogrify the terminator instruction
// to not contain the outgoing branch, or to create a new terminator
// if the form fundamentally changes (i.e., unconditional branch to
// return). Note that this will change a branch into an infinite
// loop into a return instruction!
//
RemoveSuccessor(TI, i);
// RemoveSuccessor may replace TI... make sure we have a fresh
// pointer... and e variable.
//
TI = BB->getTerminator();
// Rescan this successor...
--i;
} else {
PostDominatorTree::Node *NextNode = LastNode->getIDom();
if (LastNode) {
NextNode = LastNode->getIDom();
while (!AliveBlocks.count(NextNode->getBlock())) {
LastNode = NextNode;
NextNode = NextNode->getIDom();
if (NextNode == 0) {
LastNode = 0;
break;
}
}
}
// There is a special case here... if there IS no post-dominator for
// the block we have nowhere to point our branch to. Instead, convert
// it to a return. This can only happen if the code branched into an
// infinite loop. Note that this may not be desirable, because we
// _are_ altering the behavior of the code. This is a well known
// drawback of ADCE, so in the future if we choose to revisit the
// decision, this is where it should be.
//
if (LastNode == 0) { // No postdominator!
if (!isa<InvokeInst>(TI)) {
// Call RemoveSuccessor to transmogrify the terminator instruction
// to not contain the outgoing branch, or to create a new
// terminator if the form fundamentally changes (i.e.,
// unconditional branch to return). Note that this will change a
// branch into an infinite loop into a return instruction!
//
RemoveSuccessor(TI, i);
// RemoveSuccessor may replace TI... make sure we have a fresh
// pointer.
//
TI = BB->getTerminator();
// Rescan this successor...
--i;
} else {
}
} else {
// Get the basic blocks that we need...
BasicBlock *LastDead = LastNode->getBlock();
BasicBlock *NextAlive = NextNode->getBlock();