Substantially optimize APFloat::toString() by doing a single large divide to cut the significand down to the desired precision *before* entering the core divmod loop.  Makes the overall algorithm logarithmic in the exponent.
Substantially optimize APFloat::toString() by doing a single large divide to
cut the significand down to the desired precision *before* entering the
core divmod loop.  Makes the overall algorithm logarithmic in the exponent.

There's still a lot of room for improvement here, but this gets the
performance back down to acceptable-for-diagnostics levels, even for
long doubles.
negligible, even on long doubles.



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@92130 91177308-0d34-0410-b5e6-96231b3b80d8

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