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All three JNode compilers (l1a, l1b, l2) ✅ PASS for iconst_4 spec compliance #560

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All three JNode compilers (l1a, l1b, l2) ✅ PASS for iconst_4 spec compliance #560

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58 changes: 58 additions & 0 deletions iconst_4_spec_compliance.md
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## Spec compliance report

| Compiler | Status | Issues |
|----------|--------|--------|
| l1a | ✅ PASS | None |
| l1b | ✅ PASS | None |
| l2 | ✅ PASS | None |

---

## Details

### l1a Implementation
- **Status:** ✅ PASS
- **Files:** `core/src/core/org/jnode/vm/x86/compiler/l1a/X86BytecodeVisitor.java:2161`, `core/src/core/org/jnode/vm/x86/compiler/l1a/ItemFactory.java:61`, `core/src/core/org/jnode/vm/x86/compiler/l1a/IntItem.java:60`, `core/src/core/org/jnode/vm/x86/compiler/l1a/Item.java:250`
- **Issues:** None

**Analysis:**
- BytecodeParser (line 174) correctly decodes opcode 0x07 → `handler.visit_iconst(4)`
- X86BytecodeVisitor.visit_iconst() pushes an IntItem with JvmType.INT via ItemFactory.createIConst()
- IntItem.getType() returns JvmType.INT (category 1)
- Item.getCategory() returns 1 (correct for int)
- VirtualStack correctly tracks the single-slot push

### l1b Implementation
- **Status:** ✅ PASS
- **Files:** `core/src/core/org/jnode/vm/x86/compiler/l1b/X86BytecodeVisitor.java:2604`, `core/src/core/org/jnode/vm/x86/compiler/l1b/ItemFactory.java:56`, `core/src/core/org/jnode/vm/x86/compiler/l1b/IntItem.java:61`, `core/src/core/org/jnode/vm/x86/compiler/l1b/Item.java:235`
- **Issues:** None

**Analysis:**
- Identical implementation pattern to l1a
- Adds bytecode counter for profiling
- IntItem extends WordItem with JvmType.INT, category 1
- VirtualStack correctly handles the push

### l2 Implementation
- **Status:** ✅ PASS
- **Files:** `core/src/core/org/jnode/vm/compiler/ir/IRGenerator.java:275`, `core/src/core/org/jnode/vm/x86/compiler/l2/GenericX86CodeGenerator.java:241`, `core/src/core/org/jnode/vm/compiler/ir/IntConstant.java:26`
- **Issues:** None

**Analysis:**
- IRGenerator.visit_iconst() creates ConstantRefAssignQuad with IntConstant(value)
- Stack offset incremented by 1 (category 1)
- GenericX86CodeGenerator.generateCodeFor(ConstantRefAssignQuad) emits MOV_Const to register or stack
- L2ByteCodeSupportChecker does not override visit_iconst (inherits empty impl from BytecodeVisitorSupport) — this is correct as the checker only validates L2 eligibility, actual compilation uses IRGenerator

---

## JVM Spec References
- **Spec Base:** https://docs.oracle.com/javase/specs/jvms/se6/html/Instructions.doc.html
- **Spec Page:** https://docs.oracle.com/javase/specs/jvms/se6/html/Instructions2.doc6.html#iconst
- **Operation:** Push `int` constant
- **Format:** `iconst_<i>`
- **Forms:** `iconst_4` = 7 (0x7)
- **Operand Stack:** `...` → `..., <i>`
- **Description:** Push the `int` constant `<i>` (-1, 0, 1, 2, 3, 4 or 5) onto the operand stack
- **Notes:** Equivalent to `bipush <i>` except operand is implicit
- **Category:** 1 (int is a category-1 computational type per JVM Spec §2.11.1)
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