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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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61
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, // Merge basic blocks into their predecessor if there is only one distinct
// and if there is only one successor of the predecessor. // pred, and if there is only one distinct successor of the predecessor, and
pred_iterator PI(pred_begin(BB)); // if there are no PHI nodes.
if (PI != pred_end(BB) && *PI != BB && // Not empty? Not same BB? //
++PI == pred_end(BB) && !BB->hasConstantReferences()) { if (!isa<PHINode>(BB->front()) && !BB->hasConstantReferences()) {
BasicBlock *Pred = *pred_begin(BB); pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
TerminatorInst *Term = Pred->getTerminator(); BasicBlock *OnlyPred = *PI++;
assert(Term != 0 && "malformed basic block without terminator!"); for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
if (*PI != OnlyPred) {
OnlyPred = 0; // There are multiple different predecessors...
break;
}
// Does the predecessor block only have a single successor? BasicBlock *OnlySucc = 0;
succ_iterator SI(succ_begin(Pred)); if (OnlyPred && OnlyPred != BB) { // Don't break self loops
if (++SI == succ_end(Pred)) { // 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; //cerr << "Merging: " << BB << "into: " << Pred;
TerminatorInst *Term = OnlyPred->getTerminator();
// Delete the unconditianal branch from the predecessor... // Delete the unconditional branch from the predecessor...
BasicBlock::iterator DI = Pred->end(); BasicBlock::iterator DI = OnlyPred->end();
assert(Pred->getTerminator() && delete OnlyPred->getInstList().remove(--DI); // Destroy branch
"Degenerate basic block encountered!"); // Empty bb???
delete Pred->getInstList().remove(--DI); // Destroy uncond branch
// Move all definitions in the succecessor to the predecessor... // Move all definitions in the succecessor to the predecessor...
while (!BB->empty()) { std::vector<Instruction*> Insts(BB->begin(), BB->end());
DI = BB->begin(); BB->getInstList().remove(BB->begin(), BB->end());
Instruction *Def = BB->getInstList().remove(DI); // Remove from front OnlyPred->getInstList().insert(OnlyPred->end(),
Pred->getInstList().push_back(Def); // Add to end... Insts.begin(), Insts.end());
}
// Remove basic block from the function... and advance iterator to the // Remove basic block from the function... and advance iterator to the
// next valid block... // 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 // Make all PHI nodes that refered to BB now refer to Pred as their
// source... // source...
BB->replaceAllUsesWith(Pred); BB->replaceAllUsesWith(OnlyPred);
// Inherit predecessors name if it exists... // 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 delete BB; // You ARE the weakest link... goodbye
return true; return true;