cmd/internal/obj/riscv: handle MOV rewrites in separate pass

Handle the rewriting of MOV pseudo-instructions in a separate pass. This allows
AMOV to be more readily used by other code, including AGETCALLERPC and ARET
implementations.

Updates #27532

Change-Id: Iea794121210048ed23ed0fb8f3c5e3cd5354a311
Reviewed-on: https://go-review.googlesource.com/c/go/+/212758Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/obj/riscv/obj.go

@@ -594,9 +594,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 	// Additional instruction rewriting. Any rewrites that change the number
 	// of instructions must occur here (before jump target resolution).
 	for p := cursym.Func.Text; p != nil; p = p.Link {
-		if p.As == obj.AGETCALLERPC {
-			// Handle AGETCALLERPC early so we can use AMOV, which is then
-			// rewritten below.
+		switch p.As {
+		case obj.AGETCALLERPC:
 			if cursym.Leaf() {
 				// MOV LR, Rd
 				p.As = AMOV
@@ -608,14 +607,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				p.From.Type = obj.TYPE_MEM
 				p.From.Reg = REG_SP
 			}
-		}
-
-		switch p.As {
-		case AMOV, AMOVB, AMOVH, AMOVW, AMOVBU, AMOVHU, AMOVWU, AMOVF, AMOVD:
-			// Rewrite MOV pseudo-instructions. This cannot be done in
-			// progedit, as SP offsets need to be applied before we split
-			// up some of the Addrs.
-			rewriteMOV(ctxt, newprog, p)
 
 		case obj.ACALL:
 			switch p.To.Type {
@@ -666,6 +657,16 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		}
 	}
 
+	// Rewrite MOV pseudo-instructions. This cannot be done in
+	// progedit, as SP offsets need to be applied before we split
+	// up some of the Addrs.
+	for p := cursym.Func.Text; p != nil; p = p.Link {
+		switch p.As {
+		case AMOV, AMOVB, AMOVH, AMOVW, AMOVBU, AMOVHU, AMOVWU, AMOVF, AMOVD:
+			rewriteMOV(ctxt, newprog, p)
+		}
+	}
+
 	// Split immediates larger than 12-bits.
 	for p := cursym.Func.Text; p != nil; p = p.Link {
 		switch p.As {