All three JIT tiers (L1A, L1B, L2) PASS fstore_1 spec compliance.

[opencode-agent]

Spec compliance report

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

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Details

l1a Implementation

• Status: ✅ PASS
• Files: core/src/core/org/jnode/vm/x86/compiler/l1a/X86BytecodeVisitor.java:1850, core/src/core/org/jnode/vm/x86/compiler/l1a/X86BytecodeVisitor.java:4375 (wstore)
• Issues: None

Analysis:
The L1A compiler correctly handles fstore_1 through the standard visit_fstore(int index) pathway:

1. BytecodeParser (BytecodeParser.java:393-394) correctly decodes opcode 0x44 and calls handler.visit_fstore(1) with the implicit index 1.
2. X86BytecodeVisitor.visit_fstore (X86BytecodeVisitor.java:1850) delegates to wstore(JvmType.FLOAT, index).
3. wstore (X86BytecodeVisitor.java:4375-4421) correctly:
   • Computes the frame offset via stackFrame.getEbpOffset(typeSizeInfo, index) (index=1)
   • Pins aliases via vstack.loadLocal(eContext, disp)
   • Pops a WordItem of type FLOAT from the virtual stack
   • Handles all value states: CONSTANT (via Float.floatToRawIntBits + MOV_Const), FPUSTACK (via FSTP32), STACK (via POP), and GPR (via MOV)
   • Releases the item after store

The implementation matches the JVM spec: pops a float from the operand stack, performs value-set conversion (implicit in bitwise representation), and stores to local variable 1. Category-1 (single-slot) handling is correct for float.

l1b Implementation

• Status: ✅ PASS
• Files: core/src/core/org/jnode/vm/x86/compiler/l1b/X86BytecodeVisitor.java:2235, core/src/core/org/jnode/vm/x86/compiler/l1b/X86BytecodeVisitor.java:5368 (wstore)
• Issues: None

Analysis:
L1B mirrors L1A's structure with minor additions:

1. visit_fstore (X86BytecodeVisitor.java:2235-2240) adds bytecode counting then calls wstore(JvmType.FLOAT, index).
2. wstore (X86BytecodeVisitor.java:5368-5424) is functionally identical to L1A's but adds constLocals tracking for constant propagation optimization.
3. All value-state handling (CONSTANT, FPUSTACK, STACK, GPR) is correct and matches the spec's operand stack effect (..., value → ...).

The wide prefix is correctly NOT handled for fstore_1 (BytecodeParser.java:827-872 only includes base fstore 0x38 in the wide opcode list, not fstore_), per JVM spec.

l2 Implementation

• Status: ✅ PASS
• Files:
  • core/src/core/org/jnode/vm/x86/compiler/l2/L2ByteCodeSupportChecker.java (inherits default, no override → supported)
  • core/src/core/org/jnode/vm/compiler/ir/IRGenerator.java:401 (visit_fstore)
  • core/src/core/org/jnode/vm/x86/compiler/l2/GenericX86CodeGenerator.java:278 (generateCodeFor VariableRefAssignQuad)
• Issues: None

Analysis:
The L2 compiler uses an IR-based pipeline:

1. L2ByteCodeSupportChecker does not override visit_fstore, inheriting the empty implementation from BytecodeVisitorSupport → instruction is supported.
2. IRGenerator.visit_fstore (IRGenerator.java:401-406) correctly:
   • Decrements stackOffset by 1 (category-1 pop)
   • Sets Operand.FLOAT type on both local variable and stack slot
   • Emits VariableRefAssignQuad(lhs=index, rhs=stackOffset) representing the store
3. GenericX86CodeGenerator.generateCodeFor(VariableRefAssignQuad) (GenericX86CodeGenerator.java:301-344) handles the store:
   • When LHS=STACK (local var) and RHS=TOPS (operand stack top): emits os.writePOP(X86Register.EBP, disp1) at line 340
   • Frame offset computed via X86StackFrame.getEbpOffset (X86StackFrame.java:322-333) which correctly handles category-1 locals at (stackSlot - noArgs + 1) * -slotSize

The IR and codegen correctly model the JVM spec: single-slot float value popped from operand stack, stored to local variable 1. The wide prefix is not applicable to fstore_1 (implicit index), consistent with spec.

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JVM Spec References:

• fstore_1 format: fstore_1 = 68 (0x44), no operands
• Operand stack: ..., value → ... (value must be float, category 1)
• Description: "The value on the top of the operand stack must be of type float. It is popped from the operand stack and undergoes value set conversion... The value of the local variable at 1 is set to value'."
• Notes: "Each of the fstore_ instructions is the same as fstore with an index of , except that the operand is implicit."

Closes #283

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