GVN-hoist: limit hoisting depth (PR28670)
GVN-hoist: limit hoisting depth (PR28670)

This patch adds an option to specify the maximum depth in a BB at which to
consider hoisting instructions.  Hoisting instructions from a deeper level is
not profitable as it increases register pressure and compilation time.

Differential Revision: https://reviews.llvm.org/D22772

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@276713 91177308-0d34-0410-b5e6-96231b3b80d8

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