> Switch more uses of DominatorTree over to ETForest.
This change is also subtly non-trival. Specially, stuff like this:
>
> - DominatorTree::Node *BlockInLoopNode = DT->getNode
> (BlockInLoop);
> - DominatorTree::Node *IDom = DT->getNode(ExitBlock);
> + BasicBlock *IDom = ExitBlock;
>
> // Because the exit block is not in the loop, we know we
> have to get _at
> // least_ its immediate dominator.
> do {
> // Get next Immediate Dominator.
> - IDom = IDom->getIDom();
> + IDom = ET->getIDom(IDom);
>
> // If we have got to the header of the loop, then the
> instructions block
> // did not dominate the exit node, so we can't hoist it.
> - if (IDom->getBlock() == LoopHeader)
> + if (IDom == LoopHeader)
> return false;
>
> - } while (IDom != BlockInLoopNode);
> + } while (IDom != BlockInLoop);
One of the key reasons that domtree was faster to use than idom was
that traversing from a BB node to its idom was a simple pointer
dereference. In the case of idom, walking up idoms required a map
lookup for each access.
Before your change, this would walk up the idom with a series of
pointer dereferences, now we have to do map lookups. I don't see any
specific reason why the code couldn't continue to walk up the
etforest idom pointers, is there one?
-Chris
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