diff options
Diffstat (limited to 'lib/Transforms')
| -rw-r--r-- | lib/Transforms/Scalar/ADCE.cpp | 25 |
1 files changed, 23 insertions, 2 deletions
diff --git a/lib/Transforms/Scalar/ADCE.cpp b/lib/Transforms/Scalar/ADCE.cpp index 15ae767..38dcff1 100644 --- a/lib/Transforms/Scalar/ADCE.cpp +++ b/lib/Transforms/Scalar/ADCE.cpp @@ -105,8 +105,11 @@ void ADCE::markBlockAlive(BasicBlock *BB) { bind_obj(this, &ADCE::markTerminatorLive)); } - // If this basic block is live, then the terminator must be as well! - markTerminatorLive(BB); + // If this basic block is live, and it ends in an unconditional branch, then + // 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 @@ -248,6 +251,7 @@ bool ADCE::doADCE() { NewEntry->getInstList().push_back(new BranchInst(&Func->front())); Func->getBasicBlockList().push_front(NewEntry); 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 @@ -260,6 +264,23 @@ bool ADCE::doADCE() { BasicBlock *BB = I; 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. // We cannot save the number of successors in the terminator instruction // here because we may remove them if we don't have a postdominator... |