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Add brute-force dominance computation

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This commit is contained in:
Yoshi Askharoun
2025-09-24 17:46:17 -05:00
parent 7a36d81647
commit f9ab6c58c1
2 changed files with 94 additions and 69 deletions
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libs/UIX.DecompXml/ControlFlowAnalyzer.cs
+78 -59
View File
@@ -75,47 +75,63 @@ public static class ControlFlowAnalyzer
blocks.Add(block);
}
// Pass III: Resolve next and branch target blocks
for (var b = 0; b < blocks.Count; b++)
{
var block = (BasicControlFlowBlock)blocks[b];
if (block.NextOffset is not uint.MaxValue)
block = block with { Next = blocks[IndexOfBlockFromStartOffset(block.NextOffset)] };
if (block.BranchTargetOffset is not uint.MaxValue)
block = block with { BranchTarget = blocks[IndexOfBlockFromStartOffset(block.BranchTargetOffset)] };
blocks[b] = block;
}
return blocks;
int IndexOfBlockFromStartOffset(uint startOffset)
{
for (int b = 0; b <= blocks.Count; b++)
{
var block = blocks[b];
if (block.StartOffset == startOffset)
return b;
}
return -1;
}
}
public static List<IProgramBlock> CollapseBlocks(this List<IProgramBlock> blocks)
public static IProgramBlock GetByOffset(this List<IProgramBlock> blocks, uint offset)
{
for (int b = 0; b < blocks.Count; b++)
return blocks.First(b => offset >= b.StartOffset && offset <= b.EndOffset);
}
public static IProgramBlock GetByStartOffset(this List<IProgramBlock> blocks, uint offset) => blocks.FirstOrDefault(b => offset == b.StartOffset);
public static IProgramBlock GetByInstruction(this List<IProgramBlock> blocks, Instruction instruction) => blocks.GetByOffset(instruction.Offset);
public static bool IsAlwaysExecuted(this List<IProgramBlock> blocks, uint offset)
{
if (blocks.Count == 1)
return true;
// Checks if the entry node is post-dominated by the block containing this offset.
// Essentially, do all paths through this method execute code at this offset?
var blockOfInterest = blocks.GetByStartOffset(offset);
if (blockOfInterest is null)
return false;
HashSet<uint> visitedStartOffsets = [];
Stack<IProgramBlock> stack = [];
var filteredBlocks = blocks
.OrderBy(b => b.StartOffset)
.Where(b => b.StartOffset != offset);
stack.Push(filteredBlocks.First());
while (stack.Count > 0)
{
var block = blocks[b];
if (block.Body[^1].OpCode is OpCode.JumpIfFalse)
var current = stack.Pop();
if (visitedStartOffsets.Contains(current.StartOffset))
continue;
visitedStartOffsets.Add(current.StartOffset);
foreach (var childOffset in current.GetChildrenStartOffsets())
{
// If conditions always end with JMPF
if (childOffset == blockOfInterest.StartOffset)
continue;
var child = blocks.GetByStartOffset(childOffset);
stack.Push(child);
}
}
return [];
HashSet<uint> exitBlockOffsets = new(blocks
.Where(b => b.Body[^1].OpCode is OpCode.ReturnValue or OpCode.ReturnVoid)
.Select(b => b.StartOffset));
visitedStartOffsets.IntersectWith(exitBlockOffsets);
return visitedStartOffsets.Count == 0;
}
public static string SerializeToGraphviz(IEnumerable<IProgramBlock> blocks)
@@ -160,45 +176,48 @@ public interface IProgramBlock
{
uint StartOffset { get; }
uint EndOffset { get; }
uint NextOffset { get; }
List<Instruction> Body { get; }
IProgramBlock Next { get; }
uint NextOffset { get; }
bool HasEdgeTo(IProgramBlock block);
IEnumerable<uint> GetChildrenStartOffsets();
}
public abstract record ProgramBlock(uint StartOffset, uint EndOffset, List<Instruction> Body,
uint NextOffset = uint.MaxValue, IProgramBlock Next = null)
public abstract record ProgramBlock(uint StartOffset, uint EndOffset, List<Instruction> Body, uint NextOffset = uint.MaxValue)
: IProgramBlock
{
public virtual bool HasEdgeTo(IProgramBlock block) => NextOffset == block.StartOffset;
public virtual IEnumerable<uint> GetChildrenStartOffsets()
{
if (NextOffset is not uint.MaxValue)
yield return NextOffset;
}
}
public record BasicControlFlowBlock(uint StartOffset, uint EndOffset, List<Instruction> Body,
uint NextOffset = uint.MaxValue, uint BranchTargetOffset = uint.MaxValue,
IProgramBlock Next = null, IProgramBlock BranchTarget = null)
: ProgramBlock(StartOffset, EndOffset, Body, NextOffset, Next)
uint NextOffset = uint.MaxValue, uint BranchTargetOffset = uint.MaxValue)
: ProgramBlock(StartOffset, EndOffset, Body, NextOffset)
{
public override bool HasEdgeTo(IProgramBlock block) => base.HasEdgeTo(block) || BranchTargetOffset == block.StartOffset;
}
public record ConditionalControlFlowBlock(uint StartOffset, uint EndOffset, List<Instruction> Body,
uint NextOffset = uint.MaxValue, IProgramBlock Next = null,
IProgramBlock IfBlock = null, List<IProgramBlock> ElseIfBlocks = null, IProgramBlock ElseBlock = null)
: ProgramBlock(StartOffset, EndOffset, Body, NextOffset, Next)
{
public ConditionalControlFlowBlock(IProgramBlock programBlock,
IProgramBlock ifBlock = null, List<IProgramBlock> elseIfBlocks = null, IProgramBlock elseBlock = null)
: this(programBlock.StartOffset, programBlock.EndOffset, programBlock.Body,
programBlock.NextOffset, programBlock.Next, ifBlock, elseIfBlocks ?? [], elseBlock)
public override IEnumerable<uint> GetChildrenStartOffsets()
{
}
foreach (var offset in base.GetChildrenStartOffsets())
yield return offset;
public override bool HasEdgeTo(IProgramBlock block)
if (BranchTargetOffset is not uint.MaxValue)
yield return BranchTargetOffset;
}
}
public static class IProgramBlockExtensions
{
public static bool HasEdgeTo(this IProgramBlock block, IProgramBlock targetBlock, List<IProgramBlock> blocks)
{
return base.HasEdgeTo(block)
|| IfBlock.StartOffset == block.StartOffset
|| ElseIfBlocks.Any(b => b.StartOffset == block.StartOffset)
|| ElseBlock.StartOffset == block.StartOffset;
return block
.GetChildren(blocks)
.Contains(targetBlock);
}
public static IEnumerable<IProgramBlock> GetChildren(this IProgramBlock block, List<IProgramBlock> blocks)
{
foreach (var startOffset in block.GetChildrenStartOffsets())
yield return blocks.First(b => b.StartOffset == startOffset);
}
}
libs/UIX.DecompXml/Decompiler.Script.cs
+16 -10
View File
@@ -54,6 +54,11 @@ partial class Decompiler
if (jumpFalseToOffsets.Contains(instruction.Offset))
{
if (blockStack.Count < 2)
{
throw new InvalidOperationException("Expected two blocks left on the stack");
}
var currentBlock = blockStack.Pop() with { EndOffset = instruction.Offset };
currentBlock.FinalizeBlock(blockStack.Peek());
@@ -61,24 +66,25 @@ partial class Decompiler
// If multiple blocks lead to this address, then we're outside of the IF clause entirely.
// Otherwise, it's probably the start of an ELSE clause.
var currentControlBlock = controlBlocks.First(b => instruction.Offset >= b.StartOffset && instruction.Offset <= b.EndOffset);
if (controlBlocks.Count(b => b.HasEdgeTo(currentControlBlock)) <= 1)
var currentControlBlock = controlBlocks.GetByInstruction(instruction);
if (controlBlocks.Count(b => b.HasEdgeTo(currentControlBlock, controlBlocks)) <= 1)
{
blockStack.Push(new(instruction.Offset, uint.MaxValue, SyntaxKind.ElseClause, null));
}
}
if (jumpToOffsets.Contains(instruction.Offset))
if (controlBlocks.IsAlwaysExecuted(instruction.Offset))
{
// This address is code that will be unconditionally executed.
// For now, we'll assume that this is the end of IF/ELSE clauses.
while (blockStack.Count > 1)
{
if (blockStack.Peek().Kind is SyntaxKind.ElseClause)
{
var currentBlock = blockStack.Pop() with { EndOffset = instruction.Offset };
currentBlock.FinalizeBlock(blockStack.Peek());
}
var currentBlock = blockStack.Pop();
if (currentBlock.EndOffset is uint.MaxValue)
currentBlock = currentBlock with { EndOffset = instruction.Offset };
if (currentBlock.EndOffset != instruction.Offset)
break;
currentBlock.FinalizeBlock(blockStack.Peek());
}
}