cmd/compile: use CheckLoweredPhi on PPC64

This custom version is identical to CheckLoweredPhi. The addition of
CheckLoweredPhi likely raced with adding PPC64.

Change-Id: I294dcb758d312e93fb8842f4d1e12bf0f63a1e06
Reviewed-on: https://go-review.googlesource.com/28479
Run-TryBot: Michael Pratt <mpratt@google.com>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -854,17 +854,7 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		gc.Gvarlive(n)
 
 	case ssa.OpPhi:
-		// just check to make sure regalloc and stackalloc did it right
-		if v.Type.IsMemory() {
-			return
-		}
-		f := v.Block.Func
-		loc := f.RegAlloc[v.ID]
-		for _, a := range v.Args {
-			if aloc := f.RegAlloc[a.ID]; aloc != loc { // TODO: .Equal() instead?
-				v.Fatalf("phi arg at different location than phi: %v @ %v, but arg %v @ %v\n%s\n", v, loc, a, aloc, v.Block.Func)
-			}
-		}
+		gc.CheckLoweredPhi(v)
 
 	case ssa.OpPPC64LoweredNilCheck:
 		// Optimization - if the subsequent block has a load or store