[LLVMdev] Dead node removal in DAGCombiner

[Akira Hatanaka]

Is this piece of code in DAGCombiner::visitLOAD removing a dead node?

06155         if (N->use_empty()) {
06156           removeFromWorkList(N);
06157           DAG.DeleteNode(N);
06158         }

If it is, is there a reason it doesn't push its operands to the work
list as done in line 974-975?

00970     // If N has no uses, it is dead.  Make sure to revisit all
N's operands once
00971     // N is deleted from the DAG, since they too may now be dead
or may have a
00972     // reduced number of uses, allowing other xforms.
00973     if (N->use_empty() && N != &Dummy) {
00974       for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
00975         AddToWorkList(N->getOperand(i).getNode());
00976
00977       DAG.DeleteNode(N);
00978       continue;
00979     }

Or is it one of the corner cases mentioned in SelectionDAGISel.cpp:644?

00644       // Skip dead nodes. DAGCombiner is expected to eliminate
all dead nodes,
00645       // but there are currently some corner cases that it
misses. Also, this
00646       // makes it theoretically possible to disable the DAGCombiner.

I am seeing an error message "LLVM ERROR: Cannot select:" because
operands of a dead node do not get removed.