fix(parser): fold a signed parenthesised displacement expression

Assisted-by: GLM 5.3 Flash

parser/parser.go

@@ -552,6 +552,20 @@ func parseAddress(g []token.Token) ast.Address {
 			i = len(g) - len(rest)
 		}
 	}
+	// The same expression under a leading sign: -(24+8)(X6) puts the sign
+	// outside the fold.  The base group must follow for the value to
+	// commit, exactly as in the unsigned branch above.
+	if i < len(g) && (g[i].Kind == token.Minus || g[i].Kind == token.Plus) &&
+		i+1 < len(g) && g[i+1].Kind == token.LParen {
+		if v, rest, ok := foldExpr(g[i+1:]); ok && len(rest) > 0 && rest[0].Kind == token.LParen {
+			if g[i].Kind == token.Minus {
+				v = -v
+			}
+			addr.Offset = v
+			addr.HasOff = true
+			i = len(g) - len(rest)
+		}
+	}
 	// Optional leading displacement before a '(' base group.  A sign pushes
 	// the parenthesis one token further out: -4(DX) has it at i+2.
 	if isSignedNumber(g, i) {

parser/parser_test.go

@@ -634,3 +634,27 @@ func TestBareTrailingImmediate(t *testing.T) {
 		t.Errorf("jump target = %+v, want label loop", jmp.Operands[0])
 	}
 }
+
+// TestSignedParenDisplacement pins a sign before a parenthesised
+// displacement expression: -(24+8)(X6) negates the folded value and keeps
+// the base group, the shape GOROOT's riscv64 and loong64 files use.
+func TestSignedParenDisplacement(t *testing.T) {
+	file, errs := Parse("t.s", "TEXT \u00b7f(SB), NOSPLIT, $0-0\n\tMOV X7, -(24+8)(X6)\n\tMOV X7, +(16)(X6)\n\tRET\n")
+	if len(errs) > 0 {
+		t.Fatalf("parse: %v", errs)
+	}
+	text := file.Decls[0].(*ast.Text)
+	ins := text.Body[0].(*ast.Instr)
+	op := ins.Operands[1] // Plan 9 order: the destination address is last
+	if !op.Addr.HasOff || op.Addr.Offset != -32 {
+		t.Errorf("-(24+8): offset = %v hasOff=%v, want -32 true", op.Addr.Offset, op.Addr.HasOff)
+	}
+	if op.Addr.Base != "X6" {
+		t.Errorf("-(24+8): base = %q, want X6", op.Addr.Base)
+	}
+	ins = text.Body[1].(*ast.Instr)
+	op = ins.Operands[1]
+	if !op.Addr.HasOff || op.Addr.Offset != 16 || op.Addr.Base != "X6" {
+		t.Errorf("+(16): offset = %v hasOff=%v base=%q, want 16 true X6", op.Addr.Offset, op.Addr.HasOff, op.Addr.Base)
+	}
+}