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Do not even attempt to compute dominator information for unreachable blocks

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@7963 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-08-18 22:11:16 +00:00
parent fd4d8975cf
commit 24f83a15dd
1 changed files with 8 additions and 26 deletions
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34
lib/VMCore/Dominators.cpp
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@ -48,7 +48,7 @@ void DominatorSet::calculateDominatorsFromBlock(BasicBlock *RootBB) {
BasicBlock *BB = *It;
pred_iterator PI = pred_begin(BB), PEnd = pred_end(BB);
if (PI != PEnd) { // Is there SOME predecessor?
// Loop until we get to a predecessor that has had it's dom set filled
// Loop until we get to a predecessor that has had its dom set filled
// in at least once. We are guaranteed to have this because we are
// traversing the graph in DFO and have handled start nodes specially,
// except when there are unreachable blocks.
@ -63,29 +63,15 @@ void DominatorSet::calculateDominatorsFromBlock(BasicBlock *RootBB) {
if (PredSet.size())
set_intersect(WorkingSet, PredSet);
}
} else {
// Otherwise this block is unreachable. it doesn't really matter what
// we use for the dominator set for the node...
//
WorkingSet = Doms[Root];
}
} else if (BB != Root) {
// If this isn't the root basic block and it has no predecessors, it
// must be an unreachable block. Fib a bit by saying that the root node
// dominates this unreachable node. This isn't exactly true, because
// there is no path from the entry node to this node, but it is sorta
// true because any paths to this node would have to go through the
// entry node.
//
// This allows for dominator properties to be built for unreachable code
// in a reasonable manner.
//
WorkingSet = Doms[Root];
} else {
assert(BB == Root && "We got into unreachable code somehow!");
}
WorkingSet.insert(BB); // A block always dominates itself
DomSetType &BBSet = Doms[BB];
if (BBSet != WorkingSet) {
//assert(WorkingSet.size() > BBSet.size() && "Must only grow sets!");
BBSet.swap(WorkingSet); // Constant time operation!
Changed = true; // The sets changed.
}
@ -113,16 +99,12 @@ void DominatorSet::recalculate() {
// Calculate dominator sets for the reachable basic blocks...
calculateDominatorsFromBlock(Root);
// Every basic block in the function should at least dominate themselves, and
// thus every basic block should have an entry in Doms. The one case where we
// miss this is when a basic block is unreachable. To get these we now do an
// extra pass over the function, calculating dominator information for
// Loop through the function, ensuring that every basic block has at least an
// empty set of nodes. This is important for the case when there is
// unreachable blocks.
//
Function *F = Root->getParent();
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
if (Doms[I].count(I) == 0)
calculateDominatorsFromBlock(I);
for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) Doms[I];
}