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Do not mark ALL terminators live if any instruciton in the block is live. We only

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want to mark it live if it is an unconditional branch.  This fixes bug:
ADCE/2002-05-28-Crash.ll and makes this pass _much_ more useful.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6887 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2003-06-24 21:49:45 +00:00
parent e4b79d3324
commit 99c91e021a
1 changed files with 23 additions and 2 deletions
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25
lib/Transforms/Scalar/ADCE.cpp
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@ -105,8 +105,11 @@ void ADCE::markBlockAlive(BasicBlock *BB) {
bind_obj(this, &ADCE::markTerminatorLive)); bind_obj(this, &ADCE::markTerminatorLive));
} }
// If this basic block is live, then the terminator must be as well! // If this basic block is live, and it ends in an unconditional branch, then
markTerminatorLive(BB); // the branch is alive as well...
if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
if (BI->isUnconditional())
markTerminatorLive(BB);
} }
// dropReferencesOfDeadInstructionsInLiveBlock - Loop over all of the // dropReferencesOfDeadInstructionsInLiveBlock - Loop over all of the
@ -248,6 +251,7 @@ bool ADCE::doADCE() {
NewEntry->getInstList().push_back(new BranchInst(&Func->front())); NewEntry->getInstList().push_back(new BranchInst(&Func->front()));
Func->getBasicBlockList().push_front(NewEntry); Func->getBasicBlockList().push_front(NewEntry);
AliveBlocks.insert(NewEntry); // This block is always alive! AliveBlocks.insert(NewEntry); // This block is always alive!
LiveSet.insert(NewEntry->getTerminator()); // The branch is live
} }
// Loop over all of the alive blocks in the function. If any successor // Loop over all of the alive blocks in the function. If any successor
@ -260,6 +264,23 @@ bool ADCE::doADCE() {
BasicBlock *BB = I; BasicBlock *BB = I;
TerminatorInst *TI = BB->getTerminator(); TerminatorInst *TI = BB->getTerminator();
// If the terminator instruction is alive, but the block it is contained
// in IS alive, this means that this terminator is a conditional branch
// 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;
}
// Loop over all of the successors, looking for ones that are not alive. // Loop over all of the successors, looking for ones that are not alive.
// We cannot save the number of successors in the terminator instruction // We cannot save the number of successors in the terminator instruction
// here because we may remove them if we don't have a postdominator... // here because we may remove them if we don't have a postdominator...