fix(format): preserve square brackets in SIMD operands

Assisted-by: GLM 5.3 Flash

format/format_test.go

@@ -153,6 +153,121 @@ func TestOperandSpacing(t *testing.T) {
 	}
 }
 
+// TestVectorBracketSpacing pins the square-bracket operand forms of the
+// arm64 and loong64 vector syntaxes.  The lexer emits '[' and ']' as Illegal
+// tokens carrying their spelling, and renderOps must glue them back exactly
+// where they were: a register list and an element selector are load-bearing
+// operands the assembler reads out of the operand text, so no bracket may be
+// dropped, and the canonical spelling inside the brackets is tight.
+func TestVectorBracketSpacing(t *testing.T) {
+	cases := map[string]string{
+		// Register lists of one to four registers.
+		"[V21.B16]":                            "[V21.B16]",
+		"[V17.B16, V18.B16]":                   "[V17.B16, V18.B16]",
+		"[V18.D1, V19.D1, V20.D1]":             "[V18.D1, V19.D1, V20.D1]",
+		"[V14.B16, V15.B16, V16.B16, V17.B16]": "[V14.B16, V15.B16, V16.B16, V17.B16]",
+		// Element selectors.
+		"V31.B[15]":            "V31.B[15]",
+		"V19.S[0]":             "V19.S[0]",
+		"V1.D[1]":              "V1.D[1]",
+		"V11.B[11], V16.B[12]": "V11.B[11], V16.B[12]",
+		// Lists beside address operands, on either side.
+		"32(R1), [V2.B16, V3.B16]": "32(R1), [V2.B16, V3.B16]",
+		"[V2.S4, V3.S4], (R14)":    "[V2.S4, V3.S4], (R14)",
+		"(R24), [V18.D1, V19.D1]":  "(R24), [V18.D1, V19.D1]",
+		// A spaced spelling canonicalises to the tight one.
+		"[ V21.B16 ]": "[V21.B16]",
+		"V31.B [15]":  "V31.B[15]",
+	}
+	for in, want := range cases {
+		toks := lexOperands(in)
+		if got := renderOps(toks); got != want {
+			t.Errorf("renderOps(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
+// TestSIMDBracketRoundTrip formats whole functions carrying the bracket
+// shapes of the arm64 vector kernels and pins the output byte for byte.  The
+// brackets are load-bearing: formatting must not change what the file
+// assembles to, so the formatted text keeps every bracket, re-formats to
+// itself and still parses cleanly.
+func TestSIMDBracketRoundTrip(t *testing.T) {
+	in := "#include \"textflag.h\"\n" +
+		"\n" +
+		"TEXT ·f(SB), NOSPLIT, $0\n" +
+		"VDUP V31.B[15], R3\n" +
+		"VTBL V22.B16, [V28.B16], V11.B16\n" +
+		"VLD1 (R2), [V21.B16]\n" +
+		"VMOVQ $0x70, $0x80, V10\n" +
+		"RET\n"
+
+	want := "#include \"textflag.h\"\n" +
+		"\n" +
+		"TEXT ·f(SB), NOSPLIT, $0\n" +
+		"\tVDUP  V31.B[15], R3\n" +
+		"\tVTBL  V22.B16, [V28.B16], V11.B16\n" +
+		"\tVLD1  (R2), [V21.B16]\n" +
+		"\tVMOVQ $0x70, $0x80, V10\n" +
+		"\tRET\n"
+
+	got := Source(in)
+	if got != want {
+		t.Fatalf("formatting mismatch:\n--- got ---\n%q\n--- want ---\n%q", got, want)
+	}
+	if again := Source(got); again != got {
+		t.Fatalf("not idempotent:\n%q", again)
+	}
+	if n := strings.Count(got, "["); n != 3 {
+		t.Errorf("output carries %d '[', want 3:\n%s", n, got)
+	}
+	if _, errs := parser.Parse("in.s", got); len(errs) > 0 {
+		t.Errorf("formatted output no longer parses: %v", errs)
+	}
+}
+
+// TestBracketFormsRoundTrip runs every bracket shape of the vector kernels
+// through a full format pass as its own single-instruction function, where
+// the canonical form is the line itself indented: formatting must be a no-op
+// on each, so no bracket moves, vanishes or gains a space.
+func TestBracketFormsRoundTrip(t *testing.T) {
+	for _, instr := range []string{
+		"VDUP V31.B[15], V18",
+		"VDUP V19.S[3], V18.S4",
+		"VDUP V1.D[1], V2.D2",
+		"VMOV V13.S[0], R20",
+		"VMOV V11.B[11], V16.B[12]",
+		"VMOV R20, V21.B[2]",
+		"VTBL V22.B16, [V28.B16], V11.B16",
+		"VTBL V18.B8, [V17.B16, V18.B16], V22.B8",
+		"VTBL V31.B8, [V14.B16, V15.B16, V16.B16, V17.B16], V15.B8",
+		"VLD1 (R2), [V21.B16]",
+		"VLD1 (R24), [V18.D1, V19.D1, V20.D1]",
+		"VLD1 (R29), [V14.D1, V15.D1, V16.D1, V17.D1]",
+		"VLD1.P 32(R1), [V2.B16, V3.B16]",
+		"VLD1R (R1), [V9.B8]",
+		"VLD4R (R0), [V0.B8, V1.B8, V2.B8, V3.B8]",
+		"VST1 [V2.S4, V3.S4, V4.S4, V5.S4], (R14)",
+		"VST1.P [V2.B16], (R1)",
+		"VST1.P [V2.B16, V3.B16], 32(R1)",
+		"VMOVQ $0x70, $0x80, V10",
+	} {
+		src := "TEXT ·f(SB), NOSPLIT, $0\n" + instr + "\nRET\n"
+		want := "TEXT ·f(SB), NOSPLIT, $0\n\t" + instr + "\n\tRET\n"
+		got := Source(src)
+		if got != want {
+			t.Errorf("formatting %q:\n got  %q\n want %q", instr, got, want)
+			continue
+		}
+		if again := Source(got); again != got {
+			t.Errorf("not idempotent for %q:\n%q", instr, again)
+		}
+		if _, errs := parser.Parse("in.s", got); len(errs) > 0 {
+			t.Errorf("formatted output of %q no longer parses: %v", instr, errs)
+		}
+	}
+}
+
 // TestFlagListRoundTrip pins the '|' flag separator and the <ABIInternal>
 // marker through a full format pass: the bars the Go toolchain requires and
 // the ABI bracket must survive byte for byte, on TEXT and GLOBL alike.