CodeGen: BlockPlacement: Add comment about DenseMap Safety.
The use of a DenseMap in precomputeTriangleChains does not cause
non-determinism, even though it is iterated over, as the only thing the
iteration does is to insert entries into a new DenseMap, which is not iterated.
Comment only change.
llvm-svn: 300088
diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index e23f90b..4cfc128 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -1165,6 +1165,9 @@
}
}
+ // Iterating over a DenseMap is safe here, because the only thing in the body
+ // of the loop is inserting into another DenseMap (ComputedEdges).
+ // ComputedEdges is never iterated, so this doesn't lead to non-determinism.
for (auto &ChainPair : TriangleChainMap) {
TriangleChain &Chain = ChainPair.second;
// Benchmarking has shown that due to branch correlation duplicating 2 or