test(disasm): pin the vector spaces the decoder refuses

The RISC-V vector extension and the LoongArch LSX/LASX families carry
no x/arch decode tables, and the loong64 WORD directive is no
instruction: all three stay on the placeholder.  The pins record
today's refusal with the corpus rows that assemble the same bytes, so
a decoder bump that learns one of these spaces flips a row here and
asks for the naming pass to cover it.

Assisted-by: GLM 5.3

disasm/parity_test.go

@@ -128,6 +128,44 @@ func TestBranchTargetConvention(t *testing.T) {
 	// of the disassembler's text, and the fixtures carry it stripped.
 }
 
+// TestVectorSpaceStaysRejected pins the instruction spaces x/arch carries
+// no decode tables for at all: the RISC-V vector extension (riscv64.s
+// spells 40 such rows) and the LoongArch LSX/LASX vector families
+// (loong64enc1.s spells 807), plus the loong64 WORD data directive, which
+// is no instruction.  The corpus assembles every one of these encodings,
+// so the rows are honest negatives: they pin today's refusal, and a
+// decoder bump that learns one of these spaces flips a row here and asks
+// for the naming pass to cover it.
+func TestVectorSpaceStaysRejected(t *testing.T) {
+	for _, tt := range []struct {
+		a    arch.Arch
+		code []byte
+	}{
+		// riscv64.s: VANDNVV V1, V2, V3 // d7812006 and VCLMULVV V1,
+		// V2, V3 // d7a12032.
+		{arch.RISCV, []byte{0xd7, 0x81, 0x20, 0x06}},
+		{arch.RISCV, []byte{0xd7, 0xa1, 0x20, 0x32}},
+		// loong64enc1.s: VMOVQ V2, (R5)(R5) // a2144438 and the XV
+		// form // 82144838.
+		{arch.LOONG64, []byte{0xa2, 0x14, 0x44, 0x38}},
+		{arch.LOONG64, []byte{0x82, 0x14, 0x48, 0x38}},
+		// loong64enc1.s: VADDW V1, V2, V3 // 43040b70.
+		{arch.LOONG64, []byte{0x43, 0x04, 0x0b, 0x70}},
+		// loong64enc1.s: WORD $74565 // 45230100: a data word the
+		// assembler emits verbatim, no instruction to decode.
+		{arch.LOONG64, []byte{0x45, 0x23, 0x01, 0x00}},
+	} {
+		ins, err := Decode(tt.a, tt.code, 0)
+		if err != nil {
+			t.Errorf("%s % x: %v", tt.a, tt.code, err)
+			continue
+		}
+		if ins.Text != "???" {
+			t.Errorf("%s % x: %q, want the placeholder", tt.a, tt.code, ins.Text)
+		}
+	}
+}
+
 // relativeBranch reports whether the rendered text carries a PC-relative
 // or position-dependent target.  Such an operand is an address, not a
 // datum: it is faithful to the bytes only at the address the instruction