cmd/compile: fix confusion with ANDCCconst in PPC64 rules

Currently there is a an ANDconst and an ANDCCconst op in PPC64,
which is confusing since they map onto the same instruction.
One of these ops sets the result of the AND operation, and the
other sets the flag (condition register).

This converts ANDCCconst into an op with the 2 expected results:
the integer result of the AND and the flag setting. The ANDconst
op has been removed.

Note that in the PPC64 ISA the only variation of the 'and immediate'
is the one that sets the condition bit, which probably led to the
original (confusing) implementation.

This also adds a few rules to improve the use of ANDCCconst with
ISELB and some testcases to verify those improvements.

Change-Id: I523703fa4da2098eb995dc3ba744d36fa28e41d4
Reviewed-on: https://go-review.googlesource.com/c/go/+/422015
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: David Chase <[email protected]>
Reviewed-by: Paul Murphy <[email protected]>

src/cmd/compile/internal/ppc64/ssa.go

@@ -702,7 +702,7 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = v.Args[0].Reg()
 
-	case ssa.OpPPC64ADDconst, ssa.OpPPC64ANDconst, ssa.OpPPC64ORconst, ssa.OpPPC64XORconst,
+	case ssa.OpPPC64ADDconst, ssa.OpPPC64ORconst, ssa.OpPPC64XORconst,
 		ssa.OpPPC64SRADconst, ssa.OpPPC64SRAWconst, ssa.OpPPC64SRDconst, ssa.OpPPC64SRWconst,
 		ssa.OpPPC64SLDconst, ssa.OpPPC64SLWconst, ssa.OpPPC64EXTSWSLconst, ssa.OpPPC64MULLWconst, ssa.OpPPC64MULLDconst:
 		p := s.Prog(v.Op.Asm())
@@ -761,7 +761,8 @@ func ssaGenValue(s *ssagen.State, v *ssa.Value) {
 		p.From.Type = obj.TYPE_CONST
 		p.From.Offset = v.AuxInt
 		p.To.Type = obj.TYPE_REG
-		p.To.Reg = ppc64.REGTMP // discard result
+		//		p.To.Reg = ppc64.REGTMP // discard result
+		p.To.Reg = v.Reg0()
 
 	case ssa.OpPPC64MOVDaddr:
 		switch v.Aux.(type) {