[dev.ssa] cmd/compile: PPC64, FP to/from int conversions.

Passes ssa_test.

Requires a few new instructions and some scratchpad
memory to move data between G and F registers.

Also fixed comparisons to be correct in case of NaN.
Added missing instructions for run.bash.
Removed some FP registers that are apparently "reserved"
(but that are also apparently also unused except for a
gratuitous multiplication by two when y = x+x would work
just as well).

Currently failing stack splits.

Updates #16010.

Change-Id: I73b161bfff54445d72bd7b813b1479f89fc72602
Reviewed-on: https://go-review.googlesource.com/26813
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/cmd/compile/internal/ssa/config.go

@@ -31,6 +31,7 @@ type Config struct {
 	noDuffDevice    bool                       // Don't use Duff's device
 	nacl            bool                       // GOOS=nacl
 	use387          bool                       // GO386=387
+	NeedsFpScratch  bool                       // No direct move between GP and FP register sets
 	sparsePhiCutoff uint64                     // Sparse phi location algorithm used above this #blocks*#variables score
 	curFunc         *Func
 
@@ -190,6 +191,7 @@ func NewConfig(arch string, fe Frontend, ctxt *obj.Link, optimize bool) *Config
 		c.fpRegMask = fpRegMaskPPC64
 		c.FPReg = framepointerRegPPC64
 		c.noDuffDevice = true // TODO: Resolve PPC64 DuffDevice (has zero, but not copy)
+		c.NeedsFpScratch = true
 		c.hasGReg = true
 	default:
 		fe.Unimplementedf(0, "arch %s not implemented", arch)
@@ -245,6 +247,7 @@ func NewConfig(arch string, fe Frontend, ctxt *obj.Link, optimize bool) *Config
 }
 
 func (c *Config) Set387(b bool) {
+	c.NeedsFpScratch = b
 	c.use387 = b
 }