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Use MergeBlockIntoPredecessor to simplify some code.

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llvm-svn: 53735
This commit is contained in:
Owen Anderson 2008-07-17 20:00:46 +00:00
parent d26080487b
commit 8e971c22fd
1 changed files with 9 additions and 52 deletions
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61
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -2036,6 +2036,12 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
// pred, and if there is only one distinct successor of the predecessor, and
// if there are no PHI nodes.
//
if (MergeBlockIntoPredecessor(BB))
return true;
// Otherwise, if this block only has a single predecessor, and if that block
// is a conditional branch, see if we can hoist any code from this block up
// into our predecessor.
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
@ -2043,57 +2049,7 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
OnlyPred = 0; // There are multiple different predecessors...
break;
}
BasicBlock *OnlySucc = 0;
if (OnlyPred && OnlyPred != BB && // Don't break self loops
OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
// 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) {
DOUT << "Merging: " << *BB << "into: " << *OnlyPred;
// Resolve any PHI nodes at the start of the block. They are all
// guaranteed to have exactly one entry if they exist, unless there are
// multiple duplicate (but guaranteed to be equal) entries for the
// incoming edges. This occurs when there are multiple edges from
// OnlyPred to OnlySucc.
//
while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
PN->replaceAllUsesWith(PN->getIncomingValue(0));
BB->getInstList().pop_front(); // Delete the phi node.
}
// Delete the unconditional branch from the predecessor.
OnlyPred->getInstList().pop_back();
// Move all definitions in the successor to the predecessor.
OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
// Make all PHI nodes that referred to BB now refer to Pred as their
// source.
BB->replaceAllUsesWith(OnlyPred);
// Inherit predecessors name if it exists.
if (!OnlyPred->hasName())
OnlyPred->takeName(BB);
// Erase basic block from the function.
M->getBasicBlockList().erase(BB);
return true;
}
// Otherwise, if this block only has a single predecessor, and if that block
// is a conditional branch, see if we can hoist any code from this block up
// into our predecessor.
if (OnlyPred)
if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
if (BI->isConditional()) {
@ -2101,6 +2057,7 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
PI = pred_begin(OtherBB);
++PI;
if (PI == pred_end(OtherBB)) {
// We have a conditional branch to two blocks that are only reachable
// from the condbr. We know that the condbr dominates the two blocks,
@ -2108,7 +2065,7 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
// blocks. If so, we can hoist it up to the branching block.
Changed |= HoistThenElseCodeToIf(BI);
} else {
OnlySucc = NULL;
BasicBlock* OnlySucc = NULL;
for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
SI != SE; ++SI) {
if (!OnlySucc)