Fix issues with ISD::FNEG and ISD::FMA SDNodes where they would not be constant-folded during DAGCombine in certain circumstances.  Unfortunately, the circumstances required to trigger the issue seem to require a pretty specific interaction of DAGCombines, and I haven't been able to find a testcase that reproduces on X86, ARM, or AArch64. The functionality added here is replicated in essentially every other DAG combine, so it seems pretty obviously correct.
Fix issues with ISD::FNEG and ISD::FMA SDNodes where they would not be constant-folded
during DAGCombine in certain circumstances.  Unfortunately, the circumstances required
to trigger the issue seem to require a pretty specific interaction of DAGCombines,
and I haven't been able to find a testcase that reproduces on X86, ARM, or AArch64.
The functionality added here is replicated in essentially every other DAG combine,
so it seems pretty obviously correct.



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@214622 91177308-0d34-0410-b5e6-96231b3b80d8

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