diff options
| -rw-r--r-- | llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 59 |
1 files changed, 58 insertions, 1 deletions
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 591b2c7694a..69e2ce198e0 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -11142,7 +11142,7 @@ void DAGCombiner::GatherAllAliases(SDNode *N, SDValue OriginalChain, if (Depth > 6 || Aliases.size() == 2) { Aliases.clear(); Aliases.push_back(OriginalChain); - break; + return; } // Don't bother if we've been before. @@ -11204,6 +11204,63 @@ void DAGCombiner::GatherAllAliases(SDNode *N, SDValue OriginalChain, break; } } + + // We need to be careful here to also search for aliases through the + // value operand of a store, etc. Consider the following situation: + // Token1 = ... + // L1 = load Token1, %52 + // S1 = store Token1, L1, %51 + // L2 = load Token1, %52+8 + // S2 = store Token1, L2, %51+8 + // Token2 = Token(S1, S2) + // L3 = load Token2, %53 + // S3 = store Token2, L3, %52 + // L4 = load Token2, %53+8 + // S4 = store Token2, L4, %52+8 + // If we search for aliases of S3 (which loads address %52), and we look + // only through the chain, then we'll miss the trivial dependence on L1 + // (which also loads from %52). We then might change all loads and + // stores to use Token1 as their chain operand, which could result in + // copying %53 into %52 before copying %52 into %51 (which should + // happen first). + // + // The problem is, however, that searching for such data dependencies + // can become expensive, and the cost is not directly related to the + // chain depth. Instead, we'll rule out such configurations here by + // insisting that we've visited all chain users (except for users + // of the original chain, which is not necessary). When doing this, + // we need to look through nodes we don't care about (otherwise, things + // like register copies will interfere with trivial cases). + + SmallVector<const SDNode *, 16> Worklist; + for (SmallPtrSet<SDNode *, 16>::iterator I = Visited.begin(), + IE = Visited.end(); I != IE; ++I) + if (*I != OriginalChain.getNode()) + Worklist.push_back(*I); + + while (!Worklist.empty()) { + const SDNode *M = Worklist.pop_back_val(); + + // We have already visited M, and want to make sure we've visited any uses + // of M that we care about. For uses that we've not visisted, and don't + // care about, queue them to the worklist. + + for (SDNode::use_iterator UI = M->use_begin(), + UIE = M->use_end(); UI != UIE; ++UI) + if (UI.getUse().getValueType() == MVT::Other && Visited.insert(*UI)) { + if (isa<MemIntrinsicSDNode>(*UI) || isa<MemSDNode>(*UI)) { + // We've not visited this use, and we care about it (it could have an + // ordering dependency with the original node). + Aliases.clear(); + Aliases.push_back(OriginalChain); + return; + } + + // We've not visited this use, but we don't care about it. Mark it as + // visited and enqueue it to the worklist. + Worklist.push_back(*UI); + } + } } /// FindBetterChain - Walk up chain skipping non-aliasing memory nodes, looking |
