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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@300088 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed