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Generalize tail continues (#1298)

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* Generalize tail continues

* Fix DecodeBasicBlock

`Next` and `Branch` would be null, which is not the state expected by
the branch instructions. They end up branching or falling into a block
which is never populated by the `Translator`. This causes an assert to
be fired when building the CFG.

* Clean up Decode overloads

* Do not synchronize when branching into exit block

If we're branching into an exit block, that exit block will tail
continue into another translation which already has a synchronization.

* Remove A32 predicate tail continue

If `block` is not an exit block then the `block.Next` must exist (as
per the last instruction of `block`).

* Throw if decoded 0 blocks

Address gdkchan's feedback

* Rebuild block list instead of setting to null

Address gdkchan's feedback
This commit is contained in:
Ficture Seven 2020-06-18 07:37:21 +04:00 • committed by GitHub
parent d47e6f1952
commit 2b4418d42c
9 changed files with 178 additions and 240 deletions
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3
ARMeilleure/Decoders/Block.cs
View file

@ -12,6 +12,7 @@ namespace ARMeilleure.Decoders
public Block Branch { get; set; }
public bool TailCall { get; set; }
public bool Exit { get; set; }
public List<OpCode> OpCodes { get; private set; }
@ -29,7 +30,7 @@ namespace ARMeilleure.Decoders
{
int splitIndex = BinarySearch(OpCodes, rightBlock.Address);
if ((ulong)OpCodes[splitIndex].Address < rightBlock.Address)
if (OpCodes[splitIndex].Address < rightBlock.Address)
{
splitIndex++;
}

103
ARMeilleure/Decoders/Decoder.cs
View file

@ -17,16 +17,7 @@ namespace ARMeilleure.Decoders
// For lower code quality translation, we set a lower limit since we're blocking execution.
private const int MaxInstsPerFunctionLowCq = 500;
public static Block[] DecodeBasicBlock(IMemoryManager memory, ulong address, ExecutionMode mode)
{
Block block = new Block(address);
FillBlock(memory, mode, block, ulong.MaxValue);
return new Block[] { block };
}
public static Block[] DecodeFunction(IMemoryManager memory, ulong address, ExecutionMode mode, bool highCq)
public static Block[] Decode(IMemoryManager memory, ulong address, ExecutionMode mode, bool highCq, bool singleBlock)
{
List<Block> blocks = new List<Block>();
@ -42,13 +33,14 @@ namespace ARMeilleure.Decoders
{
if (!visited.TryGetValue(blkAddress, out Block block))
{
if (opsCount > instructionLimit || !memory.IsMapped(blkAddress))
{
return null;
}
block = new Block(blkAddress);
if ((singleBlock && visited.Count >= 1) || opsCount > instructionLimit || !memory.IsMapped(blkAddress))
{
block.Exit = true;
block.EndAddress = blkAddress;
}
workQueue.Enqueue(block);
visited.Add(blkAddress, block);
@ -71,6 +63,8 @@ namespace ARMeilleure.Decoders
throw new InvalidOperationException("Found duplicate block address on the list.");
}
currBlock.Exit = false;
nBlock.Split(currBlock);
blocks.Insert(nBlkIndex + 1, currBlock);
@ -78,47 +72,50 @@ namespace ARMeilleure.Decoders
continue;
}
// If we have a block after the current one, set the limit address.
ulong limitAddress = ulong.MaxValue;
if (nBlkIndex != blocks.Count)
if (!currBlock.Exit)
{
Block nBlock = blocks[nBlkIndex];
// If we have a block after the current one, set the limit address.
ulong limitAddress = ulong.MaxValue;
int nextIndex = nBlkIndex + 1;
if (nBlock.Address < currBlock.Address && nextIndex < blocks.Count)
if (nBlkIndex != blocks.Count)
{
limitAddress = blocks[nextIndex].Address;
}
else if (nBlock.Address > currBlock.Address)
{
limitAddress = blocks[nBlkIndex].Address;
}
}
Block nBlock = blocks[nBlkIndex];
FillBlock(memory, mode, currBlock, limitAddress);
int nextIndex = nBlkIndex + 1;
opsCount += currBlock.OpCodes.Count;
if (currBlock.OpCodes.Count != 0)
{
// Set child blocks. "Branch" is the block the branch instruction
// points to (when taken), "Next" is the block at the next address,
// executed when the branch is not taken. For Unconditional Branches
// (except BL/BLR that are sub calls) or end of executable, Next is null.
OpCode lastOp = currBlock.GetLastOp();
bool isCall = IsCall(lastOp);
if (lastOp is IOpCodeBImm op && !isCall)
{
currBlock.Branch = GetBlock((ulong)op.Immediate);
if (nBlock.Address < currBlock.Address && nextIndex < blocks.Count)
{
limitAddress = blocks[nextIndex].Address;
}
else if (nBlock.Address > currBlock.Address)
{
limitAddress = blocks[nBlkIndex].Address;
}
}
if (!IsUnconditionalBranch(lastOp) || isCall)
FillBlock(memory, mode, currBlock, limitAddress);
opsCount += currBlock.OpCodes.Count;
if (currBlock.OpCodes.Count != 0)
{
currBlock.Next = GetBlock(currBlock.EndAddress);
// Set child blocks. "Branch" is the block the branch instruction
// points to (when taken), "Next" is the block at the next address,
// executed when the branch is not taken. For Unconditional Branches
// (except BL/BLR that are sub calls) or end of executable, Next is null.
OpCode lastOp = currBlock.GetLastOp();
bool isCall = IsCall(lastOp);
if (lastOp is IOpCodeBImm op && !isCall)
{
currBlock.Branch = GetBlock((ulong)op.Immediate);
}
if (!IsUnconditionalBranch(lastOp) || isCall)
{
currBlock.Next = GetBlock(currBlock.EndAddress);
}
}
}
@ -135,7 +132,15 @@ namespace ARMeilleure.Decoders
}
}
TailCallRemover.RunPass(address, blocks);
if (blocks.Count == 0)
{
throw new InvalidOperationException($"Decoded 0 blocks. Entry point = 0x{address:X}.");
}
if (!singleBlock)
{
return TailCallRemover.RunPass(address, blocks);
}
return blocks.ToArray();
}

50
ARMeilleure/Decoders/Optimizations/TailCallRemover.cs
View file

@ -1,16 +1,15 @@
using ARMeilleure.Decoders;
using System;
using System;
using System.Collections.Generic;
namespace ARMeilleure.Decoders.Optimizations
{
static class TailCallRemover
{
public static void RunPass(ulong entryAddress, List<Block> blocks)
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.
// - Unconditional jump to an area outside this contiguous region will be treated as a tail call.
// - 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))
@ -19,57 +18,72 @@ namespace ARMeilleure.Decoders.Optimizations
}
const ulong allowance = 4;
Block entryBlock = blocks[entryBlockId];
int startBlockIndex = entryBlockId;
Block startBlock = entryBlock;
int endBlockIndex = entryBlockId;
Block endBlock = 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;
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;
startBlock = block;
startBlockIndex = i;
}
if (startBlockIndex == 0 && endBlockIndex == blocks.Count - 1)
{
return; // Nothing to do here.
return blocks.ToArray(); // Nothing to do here.
}
// Replace all branches to blocks outside the range with null, and force a tail call.
// Mark branches outside of contiguous region as exit blocks.
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;
block.Branch.Exit = true;
block.Branch.TailCall = true;
}
}
// Finally, delete all blocks outside the contiguous range.
var newBlocks = new List<Block>(blocks.Count);
blocks.RemoveRange(endBlockIndex + 1, (blocks.Count - endBlockIndex) - 1);
blocks.RemoveRange(0, startBlockIndex);
// 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();
}
}
}