cmd/internal/obj/riscv: add missing instructions to the ternary expansion list

Updates #27532

Change-Id: I5beb7941c204755948350b181c713b046bc4f1f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/215841
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/internal/obj/riscv/obj.go b/src/cmd/internal/obj/riscv/obj.go
index 53cd860..5201581 100644
--- a/src/cmd/internal/obj/riscv/obj.go
+++ b/src/cmd/internal/obj/riscv/obj.go
@@ -91,7 +91,9 @@
 	if p.Reg == 0 {
 		switch p.As {
 		case AADDI, ASLTI, ASLTIU, AANDI, AORI, AXORI, ASLLI, ASRLI, ASRAI,
-			AADD, AAND, AOR, AXOR, ASLL, ASRL, ASUB, ASRA:
+			AADD, AAND, AOR, AXOR, ASLL, ASRL, ASUB, ASRA,
+			AMUL, AMULH, AMULHU, AMULHSU, AMULW, ADIV, ADIVU, ADIVW, ADIVUW,
+			AREM, AREMU, AREMW, AREMUW:
 			p.Reg = p.To.Reg
 		}
 	}