l1a/l1b PASS; l2 FAIL (unsupported + 2/4 codepaths broken)

[opencode-agent]

Spec compliance report

Compiler	Status	Issues
l1a	✅ PASS	None
l1b	✅ PASS	None
l2	❌ FAIL	L2ByteCodeSupportChecker marks l2i as unsupported; GenericX86CodeGenerator has 2/4 code paths incorrect

---

Details

l1a Implementation

• Status: ✅ PASS
• Files: core/src/core/org/jnode/vm/x86/compiler/l1a/X86BytecodeVisitor.java:2981, core/src/core/org/jnode/vm/x86/compiler/l1a/DoubleWordItem.java, core/src/core/org/jnode/vm/x86/compiler/l1a/VirtualStack.java:178
• Issues: None

Analysis:

• Correctly implements JVM spec for l2i (opcode 0x88): converts long to int by taking low-order 32 bits
• visit_l2i() at line 2981: pops LongItem, handles constant folding ((int) v.getValue()), and for non-constants:
  • 32-bit mode (line 2989-2994): Loads long into LSB/MSB registers, releases MSB, keeps LSB (low 32 bits) as IntItem
  • 64-bit mode (line 2995-3002): Loads long into 64-bit register, gets same-group register for INT, keeps low 32 bits via register aliasing
• VirtualStack.popLong() (line 178) correctly enforces category-2 type checking
• DoubleWordItem.getLsbRegister() (line 171) provides access to low 32 bits in 32-bit mode
• Operand stack effect verified: one category-2 input (long) → one category-1 output (int)

l1b Implementation

• Status: ✅ PASS
• Files: core/src/core/org/jnode/vm/x86/compiler/l1b/X86BytecodeVisitor.java:3717, core/src/core/org/jnode/vm/x86/compiler/l1b/DoubleWordItem.java, core/src/core/org/jnode/vm/x86/compiler/l1b/VirtualStack.java:177
• Issues: None

Analysis:

• Identical logic to l1a (code duplicated)
• visit_l2i() at line 3717: same constant folding and register handling
• 32-bit mode (line 3735-3740): uses LSB register for result
• 64-bit mode (line 3741-3748): uses register aliasing for low 32 bits
• Includes counter instrumentation (l2i, l2i-const, l2i-nonconst)
• VirtualStack.popLong() (line 177) enforces category-2 type
• Operand stack effect matches spec

l2 Implementation

• Status: ❌ FAIL
• Files:
  • core/src/core/org/jnode/vm/x86/compiler/l2/L2ByteCodeSupportChecker.java:270
  • core/src/core/org/jnode/vm/x86/compiler/l2/GenericX86CodeGenerator.java:425,501,586,666
  • core/src/core/org/jnode/vm/compiler/ir/IRGenerator.java:776
  • core/src/core/org/jnode/vm/compiler/ir/Constant.java:68
  • core/src/core/org/jnode/vm/compiler/ir/quad/UnaryQuad.java:128
• Issues:
  1. L2ByteCodeSupportChecker.visit_l2i() (line 270): Explicitly calls notSupported(), throwing UnsupportedOperationException. This prevents L2 compilation of any method containing l2i.
  2. GenericX86CodeGenerator has 4 code paths for L2I, 2 are incorrect:
     • generateCodeFor(UnaryQuad, Object lhsReg, UnaryOperation, Object rhsReg) (line 425-428): Throws IllegalArgumentException for L2I
     • generateCodeFor(UnaryQuad, Object lhsReg, UnaryOperation, int rhsDisp) (line 501-503): CORRECT - MOV BITS32 lhsReg, [EBP + rhsDisp - SLOTSIZE] (loads low 32 bits)
     • generateCodeFor(UnaryQuad, int lhsDisp, UnaryOperation, int rhsDisp) (line 585-593): WRONG - Uses FPU instructions FLD32 + FISTP32 (float conversion semantics, not integer truncation)
     • generateCodeFor(UnaryQuad, int lhsDisp, UnaryOperation, int rhsDisp) (line 666-669): CORRECT - MOV BITS32 SR1, [EBP + rhsDisp - SLOTSIZE] then MOV BITS32 [EBP + lhsDisp], SR1
  3. IR Generator (IRGenerator.java:776): Correctly models stack effect: stackOffset -= 2 (pop long), setType(INT), add UnaryQuad(L2I), stackOffset += 1 (push int)
  4. Constant folding (Constant.java:68-70): Correctly implements l2i as (int) longValue
  5. UnaryQuad (UnaryQuad.java:128-129): Correctly dispatches to Constant.l2i() for constant folding

Spec References:

• JVM Spec l2i: "converted to an int result by taking the low-order 32 bits of the long value and discarding the high-order 32 bits"
• JVM Spec operand stack: ..., value → ..., result (category-2 → category-1)
• JNode L2 IR correctly models category change (2 slots → 1 slot)

Conclusion: L2 cannot compile methods with l2i due to support checker. Even if enabled, 2 of 4 code generation paths are broken (one throws, one uses wrong FPU semantics).

Closes #333

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