l1a/l1b: PARTIAL (no explicit NPE); l2: FAIL (unsupported, broken codegen)

[opencode-agent]

Spec compliance report

Compiler	Status	Issues
l1a	⚠️ PARTIAL	Missing explicit NullPointerException check (relies on implicit page fault); otherwise correct operand order, sign-extension, bounds check
l1b	⚠️ PARTIAL	Missing explicit NullPointerException check (relies on implicit page fault); otherwise correct operand order, sign-extension, bounds check
l2	❌ FAIL	saload marked unsupported in L2ByteCodeSupportChecker; GenericX86CodeGenerator.generateCodeFor(ArrayAssignQuad) ignores element type (hardcodes 32-bit, scale=4)

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Details

l1a Implementation

• Status: ⚠️ PARTIAL
• Files: core/src/core/org/jnode/vm/x86/compiler/l1a/X86BytecodeVisitor.java:3919 (visit_saload), :4045 (waload), :330 (checkBounds)
• Issues:
  • Operand stack order: Correct. waload pops IntItem idx (index) then RefItem ref (arrayref) — matches spec ..., arrayref, index → ..., value.
  • Element size & scaling: Correct for SHORT. valSize = BITS16, scale = 2 (lines 4058-4062).
  • Result type: Correct. resultType = JvmType.INT; pushes WordItem (int).
  • Sign extension: Correct. os.writeMOVSX(resultr, resultr, WORDSIZE) at line 4126 sign-extends 16-bit short to 32-bit int.
  • ArrayIndexOutOfBoundsException: Correct. checkBounds(ref, idx) emits bounds check calling SoftByteCodes.throwArrayOutOfBounds.
  • NullPointerException: ❌ Missing explicit check. No test ref, ref / jz throw_npe sequence. Relies on JNode's page fault handler (ints32.asm:406-408, ints64.asm:427-428) to convert null-page access to EX_NULLPOINTER → NullPointerException. Spec requires explicit NPE throw; implicit HW fault is implementation-dependent.

l1b Implementation

• Status: ⚠️ PARTIAL
• Files: core/src/core/org/jnode/vm/x86/compiler/l1b/X86BytecodeVisitor.java:4870 (visit_saload), :5029 (waload), :322 (checkBounds)
• Issues: Identical to l1a. Same waload implementation, same operand handling, same missing explicit null check.

l2 Implementation

• Status: ❌ FAIL
• Files: core/src/core/org/jnode/vm/x86/compiler/l2/L2ByteCodeSupportChecker.java:71, core/src/core/org/jnode/vm/x86/compiler/l2/GenericX86CodeGenerator.java:4001
• Issues:
  • L2ByteCodeSupportChecker.visit_saload() calls notSupported() (line 72) — methods containing saload never reach L2 compilation; fall back to L1.
  • IR generation exists: IRGenerator.visit_saload() (line 384) emits ArrayAssignQuad with type = Operand.SHORT.
  • Code generation broken: GenericX86CodeGenerator.generateCodeFor(ArrayAssignQuad) (line 4001) hardcodes scale = 4 and BITS32 (line 4018, 4030, 4043, etc.), ignoring quad.getType(). For SHORT it should use scale = 2, BITS16, and emit sign-extension (MOVSX).
  • checkBounds (line 4276) also lacks explicit null check (same implicit page-fault reliance).

Closes #374

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