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using ARMeilleure.Decoders;
using System;
using System.Collections.Generic;
namespace ARMeilleure.Decoders.Optimizations
{
static class TailCallRemover
{
public static void RunPass(ulong entryAddress, List<Block> blocks)
{
// Detect tail calls:
// - Assume this function spans the space covered by contiguous code blocks surrounding the entry address.
// - Unconditional jump to an area outside this contiguous region will be treated as a tail call.
// - 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];
int startBlockIndex = entryBlockId;
Block startBlock = entryBlock;
int endBlockIndex = entryBlockId;
Block endBlock = entryBlock;
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; // Nothing to do here.
}
// Replace all branches to blocks outside the range with null, and force a tail call.
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 = null;
block.TailCall = true;
}
}
// Finally, delete all blocks outside the contiguous range.
blocks.RemoveRange(endBlockIndex + 1, (blocks.Count - endBlockIndex) - 1);
blocks.RemoveRange(0, startBlockIndex);
}
}
}
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