Change FindEarliestCallSeqEnd (used by libcall insertion) to use a set to avoid revisiting nodes more than once.  This eliminates a source of potentially exponential behavior.  For a small function in 191.fma3d (hexah_stress_divergence_), this speeds up isel from taking > 20mins to taking 0.07s.
Change FindEarliestCallSeqEnd (used by libcall insertion) to use a set to
avoid revisiting nodes more than once.  This eliminates a source of
potentially exponential behavior.  For a small function in 191.fma3d
(hexah_stress_divergence_), this speeds up isel from taking > 20mins to
taking 0.07s.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@22680 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-llvm,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,apple/swift-llvm,apple/swift-llvm,chubbymaggie/asap,llvm-mirror/llvm,chubbymaggie/asap,chubbymaggie/asap,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,chubbymaggie/asap,dslab-epfl/asap,dslab-epfl/asap,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,chubbymaggie/asap,chubbymaggie/asap,dslab-epfl/asap,dslab-epfl/asap,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm