Revert "Fix the computation of linear ordering."
Build is broken.
This reverts commit 3054a90063d379ab8c9e5a42a7daf0d644b48b07.
Change-Id: I259bc2bd6a58e30391b8176f3db5fdb5c07e4d6d
diff --git a/compiler/optimizing/ssa_liveness_analysis.cc b/compiler/optimizing/ssa_liveness_analysis.cc
index 54eb581..0085b27 100644
--- a/compiler/optimizing/ssa_liveness_analysis.cc
+++ b/compiler/optimizing/ssa_liveness_analysis.cc
@@ -28,6 +28,11 @@
ComputeLiveness();
}
+static bool IsLoopExit(HLoopInformation* current, HLoopInformation* to) {
+ // `to` is either not part of a loop, or `current` is an inner loop of `to`.
+ return to == nullptr || (current != to && current->IsIn(*to));
+}
+
static bool IsLoop(HLoopInformation* info) {
return info != nullptr;
}
@@ -43,65 +48,46 @@
&& inner->IsIn(*outer);
}
-static void AddToListForLinearization(GrowableArray<HBasicBlock*>* worklist, HBasicBlock* block) {
- size_t insert_at = worklist->Size();
- HLoopInformation* block_loop = block->GetLoopInformation();
- for (; insert_at > 0; --insert_at) {
- HBasicBlock* current = worklist->Get(insert_at - 1);
- HLoopInformation* current_loop = current->GetLoopInformation();
- if (InSameLoop(block_loop, current_loop)
- || !IsLoop(current_loop)
- || IsInnerLoop(current_loop, block_loop)) {
- // The block can be processed immediately.
- break;
- }
+static void VisitBlockForLinearization(HBasicBlock* block,
+ GrowableArray<HBasicBlock*>* order,
+ ArenaBitVector* visited) {
+ if (visited->IsBitSet(block->GetBlockId())) {
+ return;
}
- worklist->InsertAt(insert_at, block);
+ visited->SetBit(block->GetBlockId());
+ size_t number_of_successors = block->GetSuccessors().Size();
+ if (number_of_successors == 0) {
+ // Nothing to do.
+ } else if (number_of_successors == 1) {
+ VisitBlockForLinearization(block->GetSuccessors().Get(0), order, visited);
+ } else {
+ DCHECK_EQ(number_of_successors, 2u);
+ HBasicBlock* first_successor = block->GetSuccessors().Get(0);
+ HBasicBlock* second_successor = block->GetSuccessors().Get(1);
+ HLoopInformation* my_loop = block->GetLoopInformation();
+ HLoopInformation* first_loop = first_successor->GetLoopInformation();
+ HLoopInformation* second_loop = second_successor->GetLoopInformation();
+
+ if (!IsLoop(my_loop)) {
+ // Nothing to do. Current order is fine.
+ } else if (IsLoopExit(my_loop, second_loop) && InSameLoop(my_loop, first_loop)) {
+ // Visit the loop exit first in post order.
+ std::swap(first_successor, second_successor);
+ } else if (IsInnerLoop(my_loop, first_loop) && !IsInnerLoop(my_loop, second_loop)) {
+ // Visit the inner loop last in post order.
+ std::swap(first_successor, second_successor);
+ }
+ VisitBlockForLinearization(first_successor, order, visited);
+ VisitBlockForLinearization(second_successor, order, visited);
+ }
+ order->Add(block);
}
void SsaLivenessAnalysis::LinearizeGraph() {
- // Create a reverse post ordering with the following properties:
- // - Blocks in a loop are consecutive,
- // - Back-edge is the last block before loop exits.
-
- // (1): Record the number of forward predecessors for each block. This is to
- // ensure the resulting order is reverse post order. We could use the
- // current reverse post order in the graph, but it would require making
- // order queries to a GrowableArray, which is not the best data structure
- // for it.
- GrowableArray<uint32_t> forward_predecessors(graph_.GetArena(), graph_.GetBlocks().Size());
- forward_predecessors.SetSize(graph_.GetBlocks().Size());
- for (size_t i = 0, e = graph_.GetBlocks().Size(); i < e; ++i) {
- HBasicBlock* block = graph_.GetBlocks().Get(i);
- size_t number_of_forward_predecessors = block->GetPredecessors().Size();
- if (block->IsLoopHeader()) {
- // We rely on having simplified the CFG.
- DCHECK_EQ(1u, block->GetLoopInformation()->NumberOfBackEdges());
- number_of_forward_predecessors--;
- }
- forward_predecessors.Put(block->GetBlockId(), number_of_foward_predecessors);
- }
-
- // (2): Following a worklist approach, first start with the entry block, and
- // iterate over the successors. When all non-back edge predecessors of a
- // successor block are visited, the successor block is added in the worklist
- // following an order that satisfies the requirements to build our linear graph.
- GrowableArray<HBasicBlock*> worklist(graph_.GetArena(), 1);
- worklist.Add(graph_.GetEntryBlock());
- do {
- HBasicBlock* current = worklist.Pop();
- linear_order_.Add(current);
- for (size_t i = 0, e = current->GetSuccessors().Size(); i < e; ++i) {
- HBasicBlock* successor = current->GetSuccessors().Get(i);
- int block_id = successor->GetBlockId();
- size_t number_of_remaining_predecessors = forward_predecessors.Get(block_id);
- if (number_of_remaining_predecessors == 1) {
- AddToListForLinearization(&worklist, successor);
- } else {
- forward_predecessors.Put(block_id, number_of_remaining_predecessors - 1);
- }
- }
- } while (!worklist.IsEmpty());
+ // For simplicity of the implementation, we create post linear order. The order for
+ // computing live ranges is the reverse of that order.
+ ArenaBitVector visited(graph_.GetArena(), graph_.GetBlocks().Size(), false);
+ VisitBlockForLinearization(graph_.GetEntryBlock(), &linear_post_order_, &visited);
}
void SsaLivenessAnalysis::NumberInstructions() {