Use PPC reciprocal estimates with Newton iteration in fast-math mode

When unsafe FP math operations are enabled, we can use the fre[s] and
frsqrte[s] instructions, which generate reciprocal (sqrt) estimates, together
with some Newton iteration, in order to quickly generate floating-point
division and sqrt results. All of these instructions are separately optional,
and so each has its own feature flag (except for the Altivec instructions,
which are covered under the existing Altivec flag). Doing this is not only
faster than using the IEEE-compliant fdiv/fsqrt instructions, but allows these
computations to be pipelined with other computations in order to hide their
overall latency.

I've also added a couple of missing fnmsub patterns which turned out to be
missing (but are necessary for good code generation of the Newton iterations).
Altivec needs a similar fix, but that will probably be more complicated because
fneg is expanded for Altivec's v4f32.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178617 91177308-0d34-0410-b5e6-96231b3b80d8
Remove some unsupported-feature comments from PPC.td

These refer to the reciprocal estimate support recently committed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178618 91177308-0d34-0410-b5e6-96231b3b80d8
Add 64-bit compare + branch for SPARC v9.

The same compare instruction is used for 32-bit and 64-bit compares. It
sets two different sets of flags: icc and xcc.

This patch adds a conditional branch instruction using the xcc flags for
64-bit compares.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178621 91177308-0d34-0410-b5e6-96231b3b80d8