private void computeAllFrames()

in src/main/java/com/amazon/corretto/hotpatch/org/objectweb/asm/MethodWriter.java [1558:1657]
71 lines of code
15 McCabe index (conditional complexity)

  private void computeAllFrames() {
    // Complete the control flow graph with exception handler blocks.
    Handler handler = firstHandler;
    while (handler != null) {
      String catchTypeDescriptor =
          handler.catchTypeDescriptor == null ? "java/lang/Throwable" : handler.catchTypeDescriptor;
      int catchType = Frame.getAbstractTypeFromInternalName(symbolTable, catchTypeDescriptor);
      // Mark handlerBlock as an exception handler.
      Label handlerBlock = handler.handlerPc.getCanonicalInstance();
      handlerBlock.flags |= Label.FLAG_JUMP_TARGET;
      // Add handlerBlock as a successor of all the basic blocks in the exception handler range.
      Label handlerRangeBlock = handler.startPc.getCanonicalInstance();
      Label handlerRangeEnd = handler.endPc.getCanonicalInstance();
      while (handlerRangeBlock != handlerRangeEnd) {
        handlerRangeBlock.outgoingEdges =
            new Edge(catchType, handlerBlock, handlerRangeBlock.outgoingEdges);
        handlerRangeBlock = handlerRangeBlock.nextBasicBlock;
      }
      handler = handler.nextHandler;
    }

    // Create and visit the first (implicit) frame.
    Frame firstFrame = firstBasicBlock.frame;
    firstFrame.setInputFrameFromDescriptor(symbolTable, accessFlags, descriptor, this.maxLocals);
    firstFrame.accept(this);

    // Fix point algorithm: add the first basic block to a list of blocks to process (i.e. blocks
    // whose stack map frame has changed) and, while there are blocks to process, remove one from
    // the list and update the stack map frames of its successor blocks in the control flow graph
    // (which might change them, in which case these blocks must be processed too, and are thus
    // added to the list of blocks to process). Also compute the maximum stack size of the method,
    // as a by-product.
    Label listOfBlocksToProcess = firstBasicBlock;
    listOfBlocksToProcess.nextListElement = Label.EMPTY_LIST;
    int maxStackSize = 0;
    while (listOfBlocksToProcess != Label.EMPTY_LIST) {
      // Remove a basic block from the list of blocks to process.
      Label basicBlock = listOfBlocksToProcess;
      listOfBlocksToProcess = listOfBlocksToProcess.nextListElement;
      basicBlock.nextListElement = null;
      // By definition, basicBlock is reachable.
      basicBlock.flags |= Label.FLAG_REACHABLE;
      // Update the (absolute) maximum stack size.
      int maxBlockStackSize = basicBlock.frame.getInputStackSize() + basicBlock.outputStackMax;
      if (maxBlockStackSize > maxStackSize) {
        maxStackSize = maxBlockStackSize;
      }
      // Update the successor blocks of basicBlock in the control flow graph.
      Edge outgoingEdge = basicBlock.outgoingEdges;
      while (outgoingEdge != null) {
        Label successorBlock = outgoingEdge.successor.getCanonicalInstance();
        boolean successorBlockChanged =
            basicBlock.frame.merge(symbolTable, successorBlock.frame, outgoingEdge.info);
        if (successorBlockChanged && successorBlock.nextListElement == null) {
          // If successorBlock has changed it must be processed. Thus, if it is not already in the
          // list of blocks to process, add it to this list.
          successorBlock.nextListElement = listOfBlocksToProcess;
          listOfBlocksToProcess = successorBlock;
        }
        outgoingEdge = outgoingEdge.nextEdge;
      }
    }

    // Loop over all the basic blocks and visit the stack map frames that must be stored in the
    // StackMapTable attribute. Also replace unreachable code with NOP* ATHROW, and remove it from
    // exception handler ranges.
    Label basicBlock = firstBasicBlock;
    while (basicBlock != null) {
      if ((basicBlock.flags & (Label.FLAG_JUMP_TARGET | Label.FLAG_REACHABLE))
          == (Label.FLAG_JUMP_TARGET | Label.FLAG_REACHABLE)) {
        basicBlock.frame.accept(this);
      }
      if ((basicBlock.flags & Label.FLAG_REACHABLE) == 0) {
        // Find the start and end bytecode offsets of this unreachable block.
        Label nextBasicBlock = basicBlock.nextBasicBlock;
        int startOffset = basicBlock.bytecodeOffset;
        int endOffset = (nextBasicBlock == null ? code.length : nextBasicBlock.bytecodeOffset) - 1;
        if (endOffset >= startOffset) {
          // Replace its instructions with NOP ... NOP ATHROW.
          for (int i = startOffset; i < endOffset; ++i) {
            code.data[i] = Opcodes.NOP;
          }
          code.data[endOffset] = (byte) Opcodes.ATHROW;
          // Emit a frame for this unreachable block, with no local and a Throwable on the stack
          // (so that the ATHROW could consume this Throwable if it were reachable).
          int frameIndex = visitFrameStart(startOffset, /* numLocal = */ 0, /* numStack = */ 1);
          currentFrame[frameIndex] =
              Frame.getAbstractTypeFromInternalName(symbolTable, "java/lang/Throwable");
          visitFrameEnd();
          // Remove this unreachable basic block from the exception handler ranges.
          firstHandler = Handler.removeRange(firstHandler, basicBlock, nextBasicBlock);
          // The maximum stack size is now at least one, because of the Throwable declared above.
          maxStackSize = Math.max(maxStackSize, 1);
        }
      }
      basicBlock = basicBlock.nextBasicBlock;
    }

    this.maxStack = maxStackSize;
  }