[SelectionDAG] Get rid of recursion in CalcNodeSethiUllmanNumber
[SelectionDAG] Get rid of recursion in CalcNodeSethiUllmanNumber

The recursive implementation of CalcNodeSethiUllmanNumber may
overflow stack on extremely long pred chains. This patch replaces it
with an equivalent iterative implementation.

Differential Revision: https://reviews.llvm.org/D33769


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@305775 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm