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 (the null-safe ?: IS_NULL, then IS_SET) - 1 case

IR Structure:

CONTROL_FLOW_CHAIN [chain_type: "ELVIS_COALESCING_OPERATOR"]
  condition_chain:
    [case 1: case_type: "EXPRESSION"]
      condition_evaluation: [LOAD lhs, lhs_set = QUESTION_OPERATOR(lhs), CALL lhs_set._false()]
      condition_result: lhs_set (EK9 Boolean)
      primitive_condition: lhs_not_set  // absent or not set
      body_evaluation: [LOAD rhs, RETAIN rhs]  // the RHS - generated ONCE, evaluated only here
      body_result: rhs
  default_body_evaluation: [RETAIN lhs]  // LHS already evaluated
  default_result: lhs

Safety: the null-safe ? (a nested QUESTION_OPERATOR chain) never calls _isSet() on an absent LHS. The RHS used to be returned by two cases - "absent" and "not set" - and generated for each, so a nested chain doubled n times.

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

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, generateCoalescingPattern, jumpTo, placeLabel, processBodyEvaluation, processConditionCase, processConditionCaseWithoutLabelPlacement, processConditionEvaluation, processInstructions, processSequentialCaseChain

Methods inherited from class AbstractAsmGenerator

convertToJvmDescriptor, convertToJvmName, extractFieldName, generateBooleanLiteral, generateCharacterLiteral, generateDebugInfo, generateFloatLiteral, generateIntegerLiteral, generateLoadVariable, generateLocalVariableTable, generateMethodDescriptor, generateObjectLiteral, generateStackOperation, generateStoreVariable, generateStoreVariableAsInt, generateStringLiteral, getCurrentMethodVisitor, getFieldDescriptor, getMethodContext, getOrCreateLabel, getOwnerClassName, getVariableIndex, isFieldAccess, isVariableAllocated, isVariableFieldAccess, setCurrentMethodVisitor, setSharedMethodContext, toJvmFieldName, 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 (:?).

Uses the common coalescing pattern from AbstractControlFlowAsmGenerator.

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