Class NullCoalescingOperatorAsmGenerator

java.lang.Object

org.ek9lang.compiler.backend.jvm.AbstractAsmGenerator

org.ek9lang.compiler.backend.jvm.AbstractControlFlowAsmGenerator

org.ek9lang.compiler.backend.jvm.NullCoalescingOperatorAsmGenerator

final class NullCoalescingOperatorAsmGenerator
extends AbstractControlFlowAsmGenerator

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

EK9 Null Coalescing Operator Pattern: lhs ?? rhs

• If LHS is null → returns RHS
• If LHS is not null → returns LHS (regardless of set/unset state)

Key Difference from Elvis Operator (:?):

• ?? checks ONLY null (IS_NULL instruction)
• :? checks BOTH null AND set (IS_NULL + IS_SET instructions)

IR Structure:

CONTROL_FLOW_CHAIN [chain_type: "NULL_COALESCING_OPERATOR"]
  condition_chain:
    [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
  default_body_evaluation: [LOAD lhs]  // Returns LHS if not null
  default_result: lhs

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
NullCoalescingOperatorAsmGenerator(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 null 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

NullCoalescingOperatorAsmGenerator

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

Method Details

generate

public void generate(ControlFlowChainInstr instr)

Generate bytecode for null coalescing operator (??).

Bytecode Pattern:

// Evaluate condition: LOAD 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:
// NOT NULL 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 NULL_COALESCING_OPERATOR type