MachineCombiner Pass for selecting faster instruction
 sequence -  AArch64 target support

 This patch turns off madd/msub generation in the DAGCombiner and generates
 them in the MachineCombiner instead. It replaces the original code sequence
 with the combined sequence when it is beneficial to do so.

 When there is no machine model support it always generates the madd/msub
 instruction. This is true also when the objective is to optimize for code
 size: when the combined sequence is shorter is always chosen and does not
 get evaluated.

 When there is a machine model the combined instruction sequence
 is evaluated for critical path and resource length using machine
 trace metrics and the original code sequence is replaced when it is
 determined to be faster.

 rdar://16319955



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214669 91177308-0d34-0410-b5e6-96231b3b80d8
fix for PR20354 - Miscompile of fabs due to vectorization

This is intended to be the minimal change needed to fix PR20354 ( http://llvm.org/bugs/show_bug.cgi?id=20354 ). The check for a vector operation was wrong; we need to check that the fabs itself is not a vector operation.

This patch will not generate the optimal code. A constant pool load and 'and' op will be generated instead of just returning a value that we can calculate in advance (as we do for the scalar case). I've put a 'TODO' comment for that here and expect to have that patch ready soon.

There is a very similar optimization that we can do in visitFNEG, so I've put another 'TODO' there and expect to have another patch for that too.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214670 91177308-0d34-0410-b5e6-96231b3b80d8