diff options
Diffstat (limited to 'llvm/lib/Transforms/Scalar/EarlyCSE.cpp')
| -rw-r--r-- | llvm/lib/Transforms/Scalar/EarlyCSE.cpp | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp index d5b9e03677f..d536a937dce 100644 --- a/llvm/lib/Transforms/Scalar/EarlyCSE.cpp +++ b/llvm/lib/Transforms/Scalar/EarlyCSE.cpp @@ -461,6 +461,30 @@ bool EarlyCSE::processNode(DomTreeNode *Node) { if (!BB->getSinglePredecessor()) ++CurrentGeneration; + // If this node has a single predecessor which ends in a conditional branch, + // we can infer the value of the branch condition given that we took this + // path. We need the single predeccesor to ensure there's not another path + // which reaches this block where the condition might hold a different + // value. Since we're adding this to the scoped hash table (like any other + // def), it will have been popped if we encounter a future merge block. + if (BasicBlock *Pred = BB->getSinglePredecessor()) + if (auto *BI = dyn_cast<BranchInst>(Pred->getTerminator())) + if (BI->isConditional()) + if (auto *CondInst = dyn_cast<Instruction>(BI->getCondition())) + if (SimpleValue::canHandle(CondInst)) { + assert(BI->getSuccessor(0) == BB || BI->getSuccessor(1) == BB); + auto *ConditionalConstant = (BI->getSuccessor(0) == BB) ? + ConstantInt::getTrue(BB->getContext()) : + ConstantInt::getFalse(BB->getContext()); + AvailableValues.insert(CondInst, ConditionalConstant); + DEBUG(dbgs() << "EarlyCSE CVP: Add conditional value for '" + << CondInst->getName() << "' as " << *ConditionalConstant + << " in " << BB->getName() << "\n"); + // Replace all dominated uses with the known value + replaceDominatedUsesWith(CondInst, ConditionalConstant, DT, + BasicBlockEdge(Pred, BB)); + } + /// LastStore - Keep track of the last non-volatile store that we saw... for /// as long as there in no instruction that reads memory. If we see a store /// to the same location, we delete the dead store. This zaps trivial dead |
