feat(arch): add the amd64 extended-instruction layer with BF16 and VP2INTERSECT

Assisted-by: GLM 5.3 Flash

asm/extension_test.go

@@ -152,14 +152,15 @@ func TestExtensionEncodable(t *testing.T) {
 	}
 }
 
-// TestExtensionArchIsolation is the architecture-binding negative case: the
-// extension layer is registered for arm64 alone, and no other architecture
-// answers its queries, not even for a mnemonic the amd64 base table carries.
+// TestExtensionArchIsolation is the architecture-binding negative case: no
+// architecture answers the arm64 mnemonics but arm64, and the amd64 layer
+// answers nothing of the arm64 family either (its own mnemonics live in
+// extension_amd64_test.go).
 func TestExtensionArchIsolation(t *testing.T) {
 	ops := []arch.ExtOperand{
 		arch.ExtVector(0, arch.ExtArrB), arch.ExtVector(0, arch.ExtArrB), arch.ExtVector(0, arch.ExtArrB),
 	}
-	for _, a := range []arch.Arch{arch.AMD64, arch.RISCV, arch.LOONG64, arch.Unknown} {
+	for _, a := range []arch.Arch{arch.RISCV, arch.LOONG64, arch.Unknown} {
 		if cands, ok := LookupExtension(a, "ADD"); ok || cands != nil {
 			t.Errorf("LookupExtension(%s, ADD) offered %d candidates", a, len(cands))
 		}
@@ -181,6 +182,24 @@ func TestExtensionArchIsolation(t *testing.T) {
 			t.Errorf("arch.Extensions(%s) carries %d instructions", a, len(got))
 		}
 	}
+	// The amd64 layer exists but stays silent about the arm64 family.
+	if cands, ok := LookupExtension(arch.AMD64, "ADD"); ok || cands != nil {
+		t.Errorf("LookupExtension(AMD64, ADD) offered %d candidates", len(cands))
+	}
+	if got, err := EncodeExtension(arch.AMD64, "ADD", ops...); err == nil {
+		t.Errorf("EncodeExtension(AMD64, ADD) encoded %x, want a refusal", got)
+	} else if !strings.Contains(err.Error(), string(arch.AMD64)) {
+		t.Errorf("EncodeExtension(AMD64) error %q does not name the architecture", err)
+	}
+	if ExtensionEncodable(arch.AMD64, "ADD", ops...) {
+		t.Error("ExtensionEncodable(AMD64, ADD) reported true")
+	}
+	if names := ExtensionNames(arch.AMD64); len(names) == 0 {
+		t.Error("the amd64 layer registers no names")
+	}
+	if got := arch.Extensions(arch.AMD64); len(got) == 0 {
+		t.Error("arch.Extensions(AMD64) is empty")
+	}
 }
 
 // TestExtensionNamesARM64 checks the completion-facing name list: every