Fix (at least) quadratic worst-case complexity in DominanceFrontier::splitBlock: don't visit all blocks in the function, and don't iterate over the split blocks' predecessor lists for each block visited.
Fix (at least) quadratic worst-case complexity in DominanceFrontier::splitBlock:
don't visit all blocks in the function, and don't iterate over the split blocks'
predecessor lists for each block visited.

Also, remove the special-case test for the entry block. Splitting the entry
block isn't common enough to make this worthwhile.

This fixes a major compile-time bottleneck which is exposed now that
LoopSimplify isn't being redundantly run both before and after
DominanceFrontier.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@109408 91177308-0d34-0410-b5e6-96231b3b80d8

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