Move early tail duplication earlier.
Move early tail duplication earlier.

This fixes the issue noted in PR10251 where early tail dup of bbs with
indirectbr would cause a bb to be duplicated into a loop preheader
and then into its predecessors, creating phi nodes with identical
operands just before register allocation.

This helps with jsinterp.o size (__TEXT goes from 163568 to 126656)
and a bit with performance 1.005x faster on sunspider (jits still enabled).

The result on webkit with the jit disabled is more significant: 1.021x faster.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@134372 91177308-0d34-0410-b5e6-96231b3b80d8

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