SelectionDAG representation shows data and instructions in the form of nodes. Similar to the
InstCombine pass in the LLVM IR, these nodes can be combined and optimized to form a minimized
SelectionDAG. But, it's not just a
DAGCombine operation that optimizes the SelectionDAG. A
DAGLegalize phase may generate some unnecessary DAG nodes, which are cleaned up by subsequent runs of the DAG optimization pass. This finally represents the
SelectionDAG in a more simple and elegant way.
How to do it…
There are lots and lots of function members (most of them are named like this:
visit**()) provided in the
DAGCombiner class to perform optimizations by folding, reordering, combining, and modifying
SDNode nodes. Note that, from the ...