Class ElvisCoalescingOperatorAsmGenerator

java.lang.Object

org.ek9lang.compiler.backend.jvm.AbstractAsmGenerator

org.ek9lang.compiler.backend.jvm.AbstractControlFlowAsmGenerator

org.ek9lang.compiler.backend.jvm.ElvisCoalescingOperatorAsmGenerator

final class ElvisCoalescingOperatorAsmGenerator
extends AbstractControlFlowAsmGenerator

Specialized generator for EK9 Elvis coalescing operator (:?). Handles CONTROL_FLOW_CHAIN with chain_type: "ELVIS_COALESCING_OPERATOR".

EK9 Elvis Coalescing Operator Pattern: lhs :? rhs

• If LHS is null → returns RHS
• If LHS is not null BUT unset → returns RHS
• If LHS is not null AND set → returns LHS

Key Difference from Null Coalescing (??):

• ?? checks ONLY null (IS_NULL instruction) - 1 case
• :? checks BOTH null AND set (IS_NULL + IS_SET instructions) - 2 cases

IR Structure:

CONTROL_FLOW_CHAIN [chain_type: "ELVIS_COALESCING_OPERATOR"]
  condition_chain:
    [case 1: case_type: "NULL_CHECK"]
      condition_evaluation: [LOAD lhs, IS_NULL lhs]
      primitive_condition: temp_is_null
      body_evaluation: [LOAD rhs]  // Returns RHS if null
      body_result: rhs
    [case 2: case_type: "EXPRESSION"]
      condition_evaluation: [CALL lhs._isSet(), CALL result._false()]
      condition_result: isSetResult (EK9 Boolean)
      primitive_condition: invertedPrimitive (NOT set)
      body_evaluation: [LOAD rhs]  // Returns RHS if unset
      body_result: rhs
  default_body_evaluation: []  // LHS already evaluated
  default_result: lhs

Safety: NULL_CHECK always precedes _isSet() call to prevent accessing unallocated memory.

Stack Frame Invariant: All paths arrive at 'end' label with empty stack. Result is stored in local variable (overall_result).

Nested Class Summary

Nested classes/interfaces inherited from class AbstractAsmGenerator

AbstractAsmGenerator.LocalVariableInfo, AbstractAsmGenerator.MethodContext, AbstractAsmGenerator.ScopeInfo, AbstractAsmGenerator.TempVariableSource

Field Summary

Fields inherited from class AbstractControlFlowAsmGenerator

context

Fields inherited from class AbstractAsmGenerator

classWriter, constructTargetTuple, outputVisitor

Constructor Summary

Constructors

Constructor	Description
ElvisCoalescingOperatorAsmGenerator(ConstructTargetTuple constructTargetTuple, OutputVisitor outputVisitor, org.objectweb.asm.ClassWriter classWriter, BytecodeGenerationContext context)

Method Summary

Modifier and Type	Method	Description
void	generate(ControlFlowChainInstr instr)	Generate bytecode for Elvis coalescing operator (:?).

Methods inherited from class AbstractControlFlowAsmGenerator

branchIfFalse, branchIfTrue, copyResultVariable, createControlFlowLabel, jumpTo, placeLabel, processBodyEvaluation, processConditionCase, processConditionCaseWithoutLabelPlacement, processConditionEvaluation, processInstructions

Methods inherited from class AbstractAsmGenerator

convertToJvmDescriptor, convertToJvmName, extractFieldName, generateBooleanLiteral, generateCharacterLiteral, generateDebugInfo, generateFloatLiteral, generateIntegerLiteral, generateLoadVariable, generateLocalVariableTable, generateMethodDescriptor, generateObjectLiteral, generateStackOperation, generateStoreVariable, generateStringLiteral, getCurrentMethodVisitor, getFieldDescriptor, getMethodContext, getOrCreateLabel, getOwnerClassName, getVariableIndex, isFieldAccess, isVariableAllocated, setCurrentMethodVisitor, setSharedMethodContext, trackTempVariableFromLiteral, trackTempVariableFromLoad

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

ElvisCoalescingOperatorAsmGenerator

ElvisCoalescingOperatorAsmGenerator(ConstructTargetTuple constructTargetTuple,
 OutputVisitor outputVisitor,
 org.objectweb.asm.ClassWriter classWriter,
 BytecodeGenerationContext context)

Method Details

generate

public void generate(ControlFlowChainInstr instr)

Generate bytecode for Elvis coalescing operator (:?).

Bytecode Pattern:

// Case 1: Check if LHS is null
ALOAD lhs_index
IFNONNULL not_null_label
// NULL case: load RHS
ALOAD rhs_index
ASTORE result_index
GOTO end_label

not_null_label:
// Case 2: Check if LHS is set (safe because not null)
ALOAD lhs_index
INVOKEVIRTUAL _isSet()
INVOKEVIRTUAL _false()  // Inverted: if NOT set
ILOAD invertedPrimitive_index
IFEQ is_set_label
// UNSET case: load RHS
ALOAD rhs_index
ASTORE result_index
GOTO end_label

is_set_label:
// SET case: load LHS
ALOAD lhs_index
ASTORE result_index

end_label:
// result now holds correct value

Stack Frame Invariant: Pre-condition: stack is empty Post-condition: stack is empty (result in local variable)

Parameters:

instr - CONTROL_FLOW_CHAIN instruction with ELVIS_COALESCING_OPERATOR type