oracle/graal · error · IllegalArgumentException

illegal call to bits on

Error message

illegal call to bits on 

What it means

JavaKind.getBitCount returns the bit width of a numeric kind (16 for Char/Short, 32 for Float/Int, 64 for Double/Long). Boolean, Void, Illegal, and Object are not in the switch, so calling getBitCount on them throws IllegalArgumentException 'illegal call to bits on <kind>'.

Source

Thrown at espresso-shared/src/com.oracle.truffle.espresso.classfile/src/com/oracle/truffle/espresso/classfile/JavaKind.java:410

    public int getBitCount() {
        switch (this) {
            case Boolean:
                return 1;
            case Byte:
                return 8;
            case Char:
            case Short:
                return 16;
            case Float:
                return 32;
            case Int:
                return 32;
            case Double:
                return 64;
            case Long:
                return 64;
            default:
                throw new IllegalArgumentException("illegal call to bits on " + this);
        }
    }

    /**
     * Returns the Espresso type (symbol) of this kind.
     *
     * @return the Espresso type (symbol) of this kind
     */
    public Symbol<Type> getType() {
        return type;
    }

    public Symbol<Name> getPrimitiveBinaryName() {
        ErrorUtil.guarantee(isPrimitive(), "not a primitive");
        return name;
    }

    public String getUnwrapMethodName() {

View on GitHub (pinned to a66e9ccd1d)

Solutions

1. Special-case Boolean (use getByteCount() == 1) and skip Object/Void/Illegal before calling getBitCount()
2. Restrict calls to kind.isPrimitive() && kind != JavaKind.Void && kind != JavaKind.Boolean

Example fix

// before
int bits = kind.getBitCount(); // fails for Boolean/Void/Object/Illegal

// after
int bits = (kind == JavaKind.Boolean) ? 1 : (kind.isPrimitive() && kind != JavaKind.Void) ? kind.getBitCount() : -1;

if (!kind.isPrimitive() || kind == JavaKind.Void || kind == JavaKind.Boolean) throw new IllegalArgumentException("no bit count for " + kind);

static boolean hasBitCount(JavaKind k) { return k.isPrimitive() && k != JavaKind.Void && k != JavaKind.Boolean; }

When it happens

Trigger: Calling getBitCount() on JavaKind.Boolean, Void, Illegal, or Object — e.g. generic sizing code computing slot widths or struct layouts over all kinds.

Common situations: Word/slot size computations that assume every kind has a bit width (Boolean is 1 byte but has no 'bits' entry here); table generation over JavaKind.values(); ports of Graal compiler code where the guard was lost.

Related errors

• illegal call to minValue on
• illegal call to maxValue on
• Expected value kind {} but got {}
• Bad argument kind at index {}: expected Boolean, got {}
• Bad argument kind at index {}: expected Byte, got {}

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/76d68137c01b5b38. Report an issue: GitHub.