test(disasm): pin the toolchain's own ADDU16I.D rendering

Assisted-by: GLM 5.3 Flash

disasm/loong64_naming_test.go

@@ -88,14 +88,30 @@ func TestUnknownNaming(t *testing.T) {
 	}
 }
 
-// TestUnknownNamingBoundaries pins what stays untouched: the macro helper
-// ADDU16I.D has no toolchain spelling (the assembler never takes it as
-// input), so its "Unknown" render is the decoder's own and stays.
+// TestUnknownNamingBoundaries pins what stays untouched: the ADDU16I.D
+// render.  The truth of the naming question, established against the live
+// toolchain: the assembler spells the family ADDV16 (loong64enc1.s pins
+// the rows and go tool asm refuses "ADDU16I.D" as input), while the
+// toolchain's own disassembler names the encoding ADDU16I.D with the
+// "Unknown" prefix x/arch gives the ops its Plan 9 map lacks, and `go tool
+// objdump` prints exactly this text ("Unknown ADDU16I.D $16, R4" for the
+// 0x10004084 the loong64enc1.s corpus carries).  The render is therefore
+// the toolchain's own on both counts, name and prefix, and stays.
 func TestUnknownNamingBoundaries(t *testing.T) {
 	for _, tt := range []struct {
 		code []byte
 		text string
 	}{
+		// loong64enc1.s: ADDV16 $(-32768<<16), R4, R5 // 85000012.
+		{[]byte{0x85, 0x00, 0x00, 0x12}, "Unknown ADDU16I.D $-32768, R4, R5"},
+		// loong64enc1.s: ADDV16 $(0<<16), R4, R5 // 85000010.
+		{[]byte{0x85, 0x00, 0x00, 0x10}, "Unknown ADDU16I.D $0, R4, R5"},
+		// loong64enc1.s: ADDV16 $(8<<16), R4, R5 // 85200010.
+		{[]byte{0x85, 0x20, 0x00, 0x10}, "Unknown ADDU16I.D $8, R4, R5"},
+		// loong64enc1.s: ADDV16 $(32767<<16), R4, R5 // 85fcff11.
+		{[]byte{0x85, 0xfc, 0xff, 0x11}, "Unknown ADDU16I.D $32767, R4, R5"},
+		// loong64enc1.s: ADDV16 $(16<<16), R4 // 84400010; the destination-
+		// only form collapses in the renderer when rd equals rj.
 		{[]byte{0x84, 0x40, 0x00, 0x10}, "Unknown ADDU16I.D $16, R4"},
 		{[]byte{0x85, 0x00, 0x17, 0x00}, "MOVW R4, R5"},
 	} {