Optimize SelectionDAG's AssignTopologicalOrder even further.
Completely eliminate the TopOrder std::vector. Instead, sort
the AllNodes list in place. This also eliminates the need to
call AllNodes.size(), a linear-time operation, before
performing the sort.
Also, eliminate the Sources temporary std::vector, since it
essentially duplicates the sorted result as it is being
built.
This also changes the direction of the topological sort
from bottom-up to top-down. The AllNodes list starts out in
roughly top-down order, so this reduces the amount of
reordering needed. Top-down is also more convenient for
Legalize, and ISel needed only minor adjustments.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56867 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index c3ab368..d6bb142 100644
--- a/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -280,11 +280,10 @@
// practice however, this causes us to run out of stack space on large basic
// blocks. To avoid this problem, compute an ordering of the nodes where each
// node is only legalized after all of its operands are legalized.
- std::vector<SDNode *> TopOrder;
- unsigned N = DAG.AssignTopologicalOrder(TopOrder);
- for (unsigned i = N; i != 0; --i)
- HandleOp(SDValue(TopOrder[i-1], 0));
- TopOrder.clear();
+ DAG.AssignTopologicalOrder();
+ for (SelectionDAG::allnodes_iterator I = DAG.allnodes_begin(),
+ E = prior(DAG.allnodes_end()); I != next(E); ++I)
+ HandleOp(SDValue(I, 0));
// Finally, it's possible the root changed. Get the new root.
SDValue OldRoot = DAG.getRoot();