using System; using System.Collections.Generic; namespace ARMeilleure.Decoders.Optimizations { static class TailCallRemover { public static Block[] RunPass(ulong entryAddress, List<Block> blocks) { // Detect tail calls: // - Assume this function spans the space covered by contiguous code blocks surrounding the entry address. // - A jump to an area outside this contiguous region will be treated as an exit block. // - Include a small allowance for jumps outside the contiguous range. if (!Decoder.BinarySearch(blocks, entryAddress, out int entryBlockId)) { throw new InvalidOperationException("Function entry point is not contained in a block."); } const ulong allowance = 4; Block entryBlock = blocks[entryBlockId]; Block startBlock = entryBlock; Block endBlock = entryBlock; int startBlockIndex = entryBlockId; int endBlockIndex = entryBlockId; for (int i = entryBlockId + 1; i < blocks.Count; i++) // Search forwards. { Block block = blocks[i]; if (endBlock.EndAddress < block.Address - allowance) { break; // End of contiguous function. } endBlock = block; endBlockIndex = i; } for (int i = entryBlockId - 1; i >= 0; i--) // Search backwards. { Block block = blocks[i]; if (startBlock.Address > block.EndAddress + allowance) { break; // End of contiguous function. } startBlock = block; startBlockIndex = i; } if (startBlockIndex == 0 && endBlockIndex == blocks.Count - 1) { return blocks.ToArray(); // Nothing to do here. } // Mark branches whose target is outside of the contiguous region as an exit block. for (int i = startBlockIndex; i <= endBlockIndex; i++) { Block block = blocks[i]; if (block.Branch != null && (block.Branch.Address > endBlock.EndAddress || block.Branch.EndAddress < startBlock.Address)) { block.Branch.Exit = true; } } var newBlocks = new List<Block>(blocks.Count); // Finally, rebuild decoded block list, ignoring blocks outside the contiguous range. for (int i = 0; i < blocks.Count; i++) { Block block = blocks[i]; if (block.Exit || (i >= startBlockIndex && i <= endBlockIndex)) { newBlocks.Add(block); } } return newBlocks.ToArray(); } } }