l1a/l1b PASS; L2 FAIL - LSHL unimplemented

[opencode-agent]

Spec compliance report

Compiler	Status	Issues
l1a	✅ PASS	None
l1b	✅ PASS	None
l2	❌ FAIL	LSHL not implemented in GenericX86CodeGenerator; all code paths throw IllegalArgumentException

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Details

l1a Implementation

• Status: ✅ PASS
• Files: core/src/core/org/jnode/vm/x86/compiler/l1a/X86BytecodeVisitor.java:3425-3466
• Issues: None

Analysis:

• Correctly pops IntItem (shift count) and LongItem (value) from virtual stack per JVM spec operand stack effect (..., value1, value2 → ..., result)
• Masks shift count with AND ECX, 63 (line 3443) implementing the spec requirement "s is the low 6 bits of value2"
• 32-bit mode (lines 3438-3457): Properly handles two cases:
  • Shift < 32: Uses SHLD_CL (v1_msb, v1_lsb) + SHL_CL (v1_lsb) for 64-bit shift
  • Shift ≥ 32: Moves LSB to MSB, zeroes LSB, then SHL_CL on MSB
• 64-bit mode (lines 3458-3461): Uses single SHL_CL on 64-bit GPR
• Releases shift count item and pushes result LongItem back to vstack
• No runtime exceptions thrown (spec-compliant)

l1b Implementation

• Status: ✅ PASS
• Files: core/src/core/org/jnode/vm/x86/compiler/l1b/X86BytecodeVisitor.java:4274-4325
• Issues: None

Analysis:

• Identical logic to l1a with same correct handling of shift count masking and 32/64-bit cases
• Includes bytecode counter instrumentation (line 4275-4277)
• Same register allocation strategy using ECX for variable shifts
• Releases shift count item and pushes result (lines 4322-4324)
• No runtime exceptions thrown (spec-compliant)

l2 Implementation

• Status: ❌ FAIL
• Files:
  • IR generation: core/src/core/org/jnode/vm/compiler/ir/IRGenerator.java:690-696 (correctly creates BinaryQuad with LSHL)
  • Support checker: core/src/core/org/jnode/vm/x86/compiler/l2/L2ByteCodeSupportChecker.java (no visit_lshl override - implicitly supported)
  • Code generation: core/src/core/org/jnode/vm/x86/compiler/l2/GenericX86CodeGenerator.java (lines 921, 1084, 1267, 1482, 1667, 1860, 2046, 2208, 2385, 2542, 2689, 2863, 3017, 3211, 3400, 3635)
• Issues: All 16 generateBinaryOP overloads in GenericX86CodeGenerator have case LSHL: that throws IllegalArgumentException("Unknown operation: " + operation). X86CodeGenerator and FPX86CodeGenerator do not override this behavior.

Impact: Any method containing lshl that gets compiled by L2 will fail at compile time with UnsupportedOperationException / IllegalArgumentException. The L2 compiler cannot compile code containing long shift-left instructions.

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JVM Spec References

JVM Spec (Java SE 6) - lshl instruction:

• Page: https://docs.oracle.com/javase/specs/jvms/se6/html/Instructions2.doc8.html
• Operation: Shift left long
• Format: lshl
• Forms: lshl = 121 (0x79)
• Operand Stack: ..., value1, value2 → ..., result
• Description: "value1 must be of type long, and value2 must be of type int. The values are popped from the operand stack. A long result is calculated by shifting value1 left by s bit positions, where s is the low 6 bits of value2."
• Notes: "The shift distance actually used is therefore always in the range 0 to 63, inclusive, as if value2 were subjected to a bitwise logical AND with the mask value 0x3f."
• Runtime Exceptions: None

Closes #352

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