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void "test3"(bool %T) {
        br bool %T, label %BB1, label %BB1
BB1:
        ret void
}


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@2472 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2002-05-06 03:02:02 +00:00
parent 4c1061f58c
commit cdac78b8a4
1 changed files with 39 additions and 26 deletions
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65
lib/Transforms/Scalar/DCE.cpp
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@ -231,43 +231,56 @@ bool SimplifyCFG(Function::iterator &BBIt) {
}
}
// Merge basic blocks into their predecessor if there is only one pred,
// and if there is only one successor of the predecessor.
pred_iterator PI(pred_begin(BB));
if (PI != pred_end(BB) && *PI != BB && // Not empty? Not same BB?
++PI == pred_end(BB) && !BB->hasConstantReferences()) {
BasicBlock *Pred = *pred_begin(BB);
TerminatorInst *Term = Pred->getTerminator();
assert(Term != 0 && "malformed basic block without terminator!");
// Does the predecessor block only have a single successor?
succ_iterator SI(succ_begin(Pred));
if (++SI == succ_end(Pred)) {
// Merge basic blocks into their predecessor if there is only one distinct
// pred, and if there is only one distinct successor of the predecessor, and
// if there are no PHI nodes.
//
if (!isa<PHINode>(BB->front()) && !BB->hasConstantReferences()) {
pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
BasicBlock *OnlyPred = *PI++;
for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
if (*PI != OnlyPred) {
OnlyPred = 0; // There are multiple different predecessors...
break;
}
BasicBlock *OnlySucc = 0;
if (OnlyPred && OnlyPred != BB) { // Don't break self loops
// Check to see if there is only one distinct successor...
succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
OnlySucc = BB;
for (; SI != SE; ++SI)
if (*SI != OnlySucc) {
OnlySucc = 0; // There are multiple distinct successors!
break;
}
}
if (OnlySucc) {
//cerr << "Merging: " << BB << "into: " << Pred;
// Delete the unconditianal branch from the predecessor...
BasicBlock::iterator DI = Pred->end();
assert(Pred->getTerminator() &&
"Degenerate basic block encountered!"); // Empty bb???
delete Pred->getInstList().remove(--DI); // Destroy uncond branch
TerminatorInst *Term = OnlyPred->getTerminator();
// Delete the unconditional branch from the predecessor...
BasicBlock::iterator DI = OnlyPred->end();
delete OnlyPred->getInstList().remove(--DI); // Destroy branch
// Move all definitions in the succecessor to the predecessor...
while (!BB->empty()) {
DI = BB->begin();
Instruction *Def = BB->getInstList().remove(DI); // Remove from front
Pred->getInstList().push_back(Def); // Add to end...
}
std::vector<Instruction*> Insts(BB->begin(), BB->end());
BB->getInstList().remove(BB->begin(), BB->end());
OnlyPred->getInstList().insert(OnlyPred->end(),
Insts.begin(), Insts.end());
// Remove basic block from the function... and advance iterator to the
// next valid block...
BB = M->getBasicBlocks().remove(BBIt);
M->getBasicBlocks().remove(BBIt);
// Make all PHI nodes that refered to BB now refer to Pred as their
// source...
BB->replaceAllUsesWith(Pred);
BB->replaceAllUsesWith(OnlyPred);
// Inherit predecessors name if it exists...
if (BB->hasName() && !Pred->hasName()) Pred->setName(BB->getName());
if (BB->hasName() && !OnlyPred->hasName())
OnlyPred->setName(BB->getName());
delete BB; // You ARE the weakest link... goodbye
return true;