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Implement test/Regression/Transforms/SimplifyCFG/UncondBranchToReturn.ll,

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see the testcase for the reasoning.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@11496 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-02-16 06:35:48 +00:00
parent 5ea27d820a
commit 19831ec853
1 changed files with 48 additions and 0 deletions
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48
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -342,6 +342,54 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
}
}
// If this is a returning block with only PHI nodes in it, fold the return
// instruction into any unconditional branch predecessors.
if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
BasicBlock::iterator BBI = BB->getTerminator();
if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
// Find predecessors that end with unconditional branches.
std::vector<BasicBlock*> UncondBranchPreds;
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
TerminatorInst *PTI = (*PI)->getTerminator();
if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
if (BI->isUnconditional())
UncondBranchPreds.push_back(*PI);
}
// If we found some, do the transformation!
if (!UncondBranchPreds.empty()) {
while (!UncondBranchPreds.empty()) {
BasicBlock *Pred = UncondBranchPreds.back();
UncondBranchPreds.pop_back();
Instruction *UncondBranch = Pred->getTerminator();
// Clone the return and add it to the end of the predecessor.
Instruction *NewRet = RI->clone();
Pred->getInstList().push_back(NewRet);
// If the return instruction returns a value, and if the value was a
// PHI node in "BB", propagate the right value into the return.
if (NewRet->getNumOperands() == 1)
if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0)))
if (PN->getParent() == BB)
NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred));
// Update any PHI nodes in the returning block to realize that we no
// longer branch to them.
BB->removePredecessor(Pred);
Pred->getInstList().erase(UncondBranch);
}
// If we eliminated all predecessors of the block, delete the block now.
if (pred_begin(BB) == pred_end(BB))
// We know there are no successors, so just nuke the block.
M->getBasicBlockList().erase(BB);
return true;
}
}
}
// 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.