cmd/internal/obj/ppc64: handle MOVDU for SP delta

If a MOVDU instruction is used with an offset of SP, the
instruction changes SP therefore needs an SP delta, which is used
for generating the PC-SP table for stack unwinding. MOVDU is
frequently used for allocating the frame and saving the LR in the
same instruction, so this is particularly useful.

Change-Id: Icb63eb55aa01c3dc350ac4e4cff6371f4c3c5867
Reviewed-on: https://go-review.googlesource.com/c/go/+/205279
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/internal/obj/ppc64/obj9.go

@@ -961,6 +961,13 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			if p.To.Type == obj.TYPE_REG && p.To.Reg == REGSP && p.From.Type == obj.TYPE_CONST {
 				p.Spadj = int32(-p.From.Offset)
 			}
+		case AMOVDU:
+			if p.To.Type == obj.TYPE_MEM && p.To.Reg == REGSP {
+				p.Spadj = int32(-p.To.Offset)
+			}
+			if p.From.Type == obj.TYPE_MEM && p.From.Reg == REGSP {
+				p.Spadj = int32(-p.From.Offset)
+			}
 		case obj.AGETCALLERPC:
 			if cursym.Leaf() {
 				/* MOVD LR, Rd */