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Fix bug: ADCE/2003-06-24-BadSuccessor.ll

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llvm-svn: 6891
This commit is contained in:
Chris Lattner 2003-06-24 23:02:45 +00:00
parent b5b462bf61
commit 2cd94ee470
1 changed files with 35 additions and 12 deletions
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47
lib/Transforms/Scalar/ADCE.cpp
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@ -73,6 +73,8 @@ private:
// instructions that are dead according to LiveSet.
bool dropReferencesOfDeadInstructionsInLiveBlock(BasicBlock *BB);
TerminatorInst *convertToUnconditionalBranch(TerminatorInst *TI);
inline void markInstructionLive(Instruction *I) {
if (LiveSet.count(I)) return;
DEBUG(std::cerr << "Insn Live: " << I);
@ -139,6 +141,24 @@ bool ADCE::dropReferencesOfDeadInstructionsInLiveBlock(BasicBlock *BB) {
}
/// convertToUnconditionalBranch - Transform this conditional terminator
/// instruction into an unconditional branch because we don't care which of the
/// successors it goes to. This eliminate a use of the condition as well.
///
TerminatorInst *ADCE::convertToUnconditionalBranch(TerminatorInst *TI) {
BranchInst *NB = new BranchInst(TI->getSuccessor(0), TI);
BasicBlock *BB = TI->getParent();
// Remove entries from PHI nodes to avoid confusing ourself later...
for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
TI->getSuccessor(i)->removePredecessor(BB);
// Delete the old branch itself...
BB->getInstList().erase(TI);
return NB;
}
// doADCE() - Run the Aggressive Dead Code Elimination algorithm, returning
// true if the function was modified.
//
@ -234,13 +254,25 @@ bool ADCE::doADCE() {
// new entry node...
//
if (AliveBlocks.size() == Func->size()) { // No dead blocks?
for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I)
for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I) {
// Loop over all of the instructions in the function, telling dead
// instructions to drop their references. This is so that the next sweep
// over the program can safely delete dead instructions without other dead
// instructions still refering to them.
//
dropReferencesOfDeadInstructionsInLiveBlock(I);
// Check to make sure the terminator instruction is live. If it isn't,
// this means that the condition that it branches on (we know it is not an
// unconditional branch), is not needed to make the decision of where to
// go to, because all outgoing edges go to the same place. We must remove
// the use of the condition (because it's probably dead), so we convert
// the terminator to a conditional branch.
//
TerminatorInst *TI = I->getTerminator();
if (!LiveSet.count(TI))
convertToUnconditionalBranch(TI);
}
} else { // If there are some blocks dead...
// If the entry node is dead, insert a new entry node to eliminate the entry
@ -269,17 +301,8 @@ bool ADCE::doADCE() {
// on a condition that doesn't matter. Make it an unconditional branch
// to ONE of the successors. This has the side effect of dropping a use
// of the conditional value, which may also be dead.
if (!LiveSet.count(TI)) {
assert(TI->getNumSuccessors() > 1 && "Not a conditional?");
BranchInst *NB = new BranchInst(TI->getSuccessor(0), TI);
// Remove entries from PHI nodes to avoid confusing ourself later...
for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
TI->getSuccessor(i)->removePredecessor(BB);
BB->getInstList().erase(TI);
TI = NB;
}
if (!LiveSet.count(TI))
TI = convertToUnconditionalBranch(TI);
// Loop over all of the successors, looking for ones that are not alive.
// We cannot save the number of successors in the terminator instruction