public static void Optimize(StructuredProgramContext context)
{
AstBlock mainBlock = context.CurrentFunction.MainBlock;
// When debug mode is enabled, we disable expression propagation
// (this makes comparison with the disassembly easier).
if ((context.Config.Options.Flags & TranslationFlags.DebugMode) == 0)
{
AstBlockVisitor visitor = new AstBlockVisitor(mainBlock);
foreach (IAstNode node in visitor.Visit())
{
if (node is AstAssignment assignment && assignment.Destination is AstOperand propVar)
{
bool isWorthPropagating = propVar.Uses.Count == 1 || IsWorthPropagating(assignment.Source);
if (propVar.Defs.Count == 1 && isWorthPropagating)
{
PropagateExpression(propVar, assignment.Source);
}
if (propVar.Type == OperandType.LocalVariable && propVar.Uses.Count == 0)
{
visitor.Block.Remove(assignment);
context.CurrentFunction.Locals.Remove(propVar);
}
}
}
}
RemoveEmptyBlocks(mainBlock);
}
private static void Lift(GotoStatement stmt)
{
AstBlock block = ParentBlock(stmt.Goto);
AstBlock[] path = BackwardsPath(block, ParentBlock(stmt.Label));
AstBlock loopFirstStmt = path[path.Length - 1];
if (loopFirstStmt.Type == AstBlockType.Else)
{
loopFirstStmt = Previous(loopFirstStmt) as AstBlock;
if (loopFirstStmt == null || loopFirstStmt.Type != AstBlockType.If)
{
throw new InvalidOperationException("Found an else without a matching if.");
}
}
AstBlock newBlock = EncloseDoWhile(stmt, block, loopFirstStmt);
block.Remove(stmt.Goto);
newBlock.AddFirst(stmt.Goto);
stmt.IsLoop = false;
}
public static void Optimize(StructuredProgramInfo info)
{
AstBlock mainBlock = info.MainBlock;
AstBlockVisitor visitor = new AstBlockVisitor(mainBlock);
foreach (IAstNode node in visitor.Visit())
{
if (node is AstAssignment assignment && assignment.Destination is AstOperand propVar)
{
bool isWorthPropagating = propVar.Uses.Count == 1 || IsWorthPropagating(assignment.Source);
if (propVar.Defs.Count == 1 && isWorthPropagating)
{
PropagateExpression(propVar, assignment.Source);
}
if (propVar.Type == OperandType.LocalVariable && propVar.Uses.Count == 0)
{
visitor.Block.Remove(assignment);
info.Locals.Remove(propVar);
}
}
}
RemoveEmptyBlocks(mainBlock);
}
private static void EncloseSingleInst(GotoStatement stmt, Instruction inst)
{
AstBlock block = ParentBlock(stmt.Goto);
AstBlock newBlock = new AstBlock(AstBlockType.If, stmt.Condition);
block.AddAfter(stmt.Goto, newBlock);
newBlock.AddFirst(new AstOperation(inst));
}
public StructuredProgramInfo(AstBlock mainBlock)
{
MainBlock = mainBlock;
Locals = new HashSet <AstOperand>();
CBuffers = new HashSet <int>();
IAttributes = new HashSet <int>();
OAttributes = new HashSet <int>();
Samplers = new HashSet <AstTextureOperation>();
}
private static AstBlock[] BackwardsPath(AstBlock top, AstBlock bottom)
{
AstBlock block = bottom;
List <AstBlock> path = new List <AstBlock>();
while (block != top)
{
path.Add(block);
block = block.Parent;
}
return(path.ToArray());
}
public StructuredFunction(
AstBlock mainBlock,
string name,
VariableType returnType,
VariableType[] inArguments,
VariableType[] outArguments)
{
MainBlock = mainBlock;
Name = name;
ReturnType = returnType;
InArguments = inArguments;
OutArguments = outArguments;
Locals = new HashSet <AstOperand>();
}
public StructuredProgramInfo(AstBlock mainBlock)
{
MainBlock = mainBlock;
Locals = new HashSet <AstOperand>();
CBuffers = new HashSet <int>();
SBuffers = new HashSet <int>();
IAttributes = new HashSet <int>();
OAttributes = new HashSet <int>();
InterpolationQualifiers = new InterpolationQualifier[32];
Samplers = new HashSet <AstTextureOperation>();
Images = new HashSet <AstTextureOperation>();
}
private static void MoveInward(GotoStatement stmt)
{
AstBlock block = ParentBlock(stmt.Goto);
AstBlock[] path = BackwardsPath(block, ParentBlock(stmt.Label));
for (int index = path.Length - 1; index >= 0; index--)
{
AstBlock child = path[index];
AstBlock last = child;
if (child.Type == AstBlockType.If)
{
// Modify the if condition to allow it to be entered by the goto.
if (!ContainsCondComb(child.Condition, Instruction.LogicalOr, stmt.Condition))
{
child.OrCondition(stmt.Condition);
}
}
else if (child.Type == AstBlockType.Else)
{
// Modify the matching if condition to force the else to be entered by the goto.
if (!(Previous(child) is AstBlock ifBlock) || ifBlock.Type != AstBlockType.If)
{
throw new InvalidOperationException("Found an else without a matching if.");
}
IAstNode cond = InverseCond(stmt.Condition);
if (!ContainsCondComb(ifBlock.Condition, Instruction.LogicalAnd, cond))
{
ifBlock.AndCondition(cond);
}
last = ifBlock;
}
Enclose(block, AstBlockType.If, stmt.Condition, Next(stmt.Goto), last);
block.Remove(stmt.Goto);
child.AddFirst(stmt.Goto);
block = child;
}
}
private static AstBlock Enclose(
AstBlock block,
AstBlockType type,
IAstNode cond,
IAstNode first,
IAstNode last = null)
{
if (first == last)
{
return(null);
}
if (type == AstBlockType.If)
{
cond = InverseCond(cond);
}
// Do a quick check, if we are enclosing a single block,
// and the block type/condition matches the one we're going
// to create, then we don't need a new block, we can just
// return the old one.
bool hasSingleNode = Next(first) == last;
if (hasSingleNode && BlockMatches(first, type, cond))
{
return(first as AstBlock);
}
AstBlock newBlock = new AstBlock(type, cond);
block.AddBefore(first, newBlock);
while (first != last)
{
IAstNode next = Next(first);
block.Remove(first);
newBlock.Add(first);
first = next;
}
return(newBlock);
}
private static bool DirectlyRelated(AstBlock lBlock, AstBlock rBlock, int lLevel, int rLevel)
{
// If the levels are equal, they can be either siblings or indirectly related.
if (lLevel == rLevel)
{
return(false);
}
IAstNode block;
IAstNode other;
int blockLvl, otherLvl;
if (lLevel > rLevel)
{
block = lBlock;
blockLvl = lLevel;
other = rBlock;
otherLvl = rLevel;
}
else /* if (rLevel > lLevel) */
{
block = rBlock;
blockLvl = rLevel;
other = lBlock;
otherLvl = lLevel;
}
while (blockLvl >= otherLvl)
{
if (block == other)
{
return(true);
}
block = block.Parent;
blockLvl--;
}
return(false);
}
private static AstBlock EncloseDoWhile(GotoStatement stmt, AstBlock block, IAstNode first)
{
if (block.Type == AstBlockType.DoWhile && first == block.First)
{
// We only need to insert the continue if we're not at the end of the loop,
// or if our condition is different from the loop condition.
if (Next(stmt.Goto) != null || block.Condition != stmt.Condition)
{
EncloseSingleInst(stmt, Instruction.LoopContinue);
}
// Modify the do-while condition to allow it to continue.
if (!ContainsCondComb(block.Condition, Instruction.LogicalOr, stmt.Condition))
{
block.OrCondition(stmt.Condition);
}
return(block);
}
return(Enclose(block, AstBlockType.DoWhile, stmt.Condition, first, stmt.Goto));
}
public IEnumerable <IAstNode> Visit()
{
IAstNode node = Block.First;
while (node != null)
{
//We reached a child block, visit the nodes inside.
while (node is AstBlock childBlock)
{
Block = childBlock;
node = childBlock.First;
BlockEntered?.Invoke(this, new BlockVisitationEventArgs(Block));
}
//Node may be null, if the block is empty.
if (node != null)
{
IAstNode next = Next(node);
yield return(node);
node = next;
}
//We reached the end of the list, go up on tree to the parent blocks.
while (node == null && Block.Type != AstBlockType.Main)
{
BlockLeft?.Invoke(this, new BlockVisitationEventArgs(Block));
node = Next(Block);
Block = Block.Parent;
}
}
}
private static void RemoveEmptyBlocks(AstBlock mainBlock)
{
Queue <AstBlock> pending = new Queue <AstBlock>();
pending.Enqueue(mainBlock);
while (pending.TryDequeue(out AstBlock block))
{
foreach (IAstNode node in block)
{
if (node is AstBlock childBlock)
{
pending.Enqueue(childBlock);
}
}
AstBlock parent = block.Parent;
if (parent == null)
{
continue;
}
AstBlock nextBlock = Next(block) as AstBlock;
bool hasElse = nextBlock != null && nextBlock.Type == AstBlockType.Else;
bool isIf = block.Type == AstBlockType.If;
if (block.Count == 0)
{
if (isIf)
{
if (hasElse)
{
nextBlock.TurnIntoIf(InverseCond(block.Condition));
}
parent.Remove(block);
}
else if (block.Type == AstBlockType.Else)
{
parent.Remove(block);
}
}
else if (isIf && parent.Type == AstBlockType.Else && parent.Count == (hasElse ? 2 : 1))
{
AstBlock parentOfParent = parent.Parent;
parent.Remove(block);
parentOfParent.AddAfter(parent, block);
if (hasElse)
{
parent.Remove(nextBlock);
parentOfParent.AddAfter(block, nextBlock);
}
parentOfParent.Remove(parent);
block.TurnIntoElseIf();
}
}
}
// This is a modified version of the algorithm presented on the paper
// "Taming Control Flow: A Structured Approach to Eliminating Goto Statements".
public static void Eliminate(GotoStatement[] gotos)
{
for (int index = gotos.Length - 1; index >= 0; index--)
{
GotoStatement stmt = gotos[index];
AstBlock gBlock = ParentBlock(stmt.Goto);
AstBlock lBlock = ParentBlock(stmt.Label);
int gLevel = Level(gBlock);
int lLevel = Level(lBlock);
if (IndirectlyRelated(gBlock, lBlock, gLevel, lLevel))
{
AstBlock drBlock = gBlock;
int drLevel = gLevel;
do
{
drBlock = drBlock.Parent;
drLevel--;
}while (!DirectlyRelated(drBlock, lBlock, drLevel, lLevel));
MoveOutward(stmt, gLevel, drLevel);
gBlock = drBlock;
gLevel = drLevel;
if (Previous(stmt.Goto) is AstBlock elseBlock && elseBlock.Type == AstBlockType.Else)
{
// It's possible that the label was enclosed inside an else block,
// in this case we need to update the block and level.
// We also need to set the IsLoop for the case when the label is
// now before the goto, due to the newly introduced else block.
lBlock = ParentBlock(stmt.Label);
lLevel = Level(lBlock);
if (!IndirectlyRelated(elseBlock, lBlock, gLevel + 1, lLevel))
{
stmt.IsLoop = true;
}
}
}
if (DirectlyRelated(gBlock, lBlock, gLevel, lLevel))
{
if (gLevel > lLevel)
{
MoveOutward(stmt, gLevel, lLevel);
}
else
{
if (stmt.IsLoop)
{
Lift(stmt);
}
MoveInward(stmt);
}
}
gBlock = ParentBlock(stmt.Goto);
if (stmt.IsLoop)
{
EncloseDoWhile(stmt, gBlock, stmt.Label);
}
else
{
Enclose(gBlock, AstBlockType.If, stmt.Condition, Next(stmt.Goto), stmt.Label);
}
gBlock.Remove(stmt.Goto);
}
}
public AstBlockVisitor(AstBlock mainBlock)
{
Block = mainBlock;
}
public BlockVisitationEventArgs(AstBlock block)
{
Block = block;
}
private static void MoveOutward(GotoStatement stmt, int gLevel, int lLevel)
{
AstBlock origin = ParentBlock(stmt.Goto);
AstBlock block = origin;
// Check if a loop is enclosing the goto, and the block that is
// directly related to the label is above the loop block.
// In that case, we need to introduce a break to get out of the loop.
AstBlock loopBlock = origin;
int loopLevel = gLevel;
while (loopLevel > lLevel)
{
AstBlock child = loopBlock;
loopBlock = loopBlock.Parent;
loopLevel--;
if (child.Type == AstBlockType.DoWhile)
{
EncloseSingleInst(stmt, Instruction.LoopBreak);
block.Remove(stmt.Goto);
loopBlock.AddAfter(child, stmt.Goto);
block = loopBlock;
gLevel = loopLevel;
}
}
// Insert ifs to skip the parts that shouldn't be executed due to the goto.
bool tryInsertElse = stmt.IsUnconditional && origin.Type == AstBlockType.If;
while (gLevel > lLevel)
{
Enclose(block, AstBlockType.If, stmt.Condition, Next(stmt.Goto));
block.Remove(stmt.Goto);
AstBlock child = block;
// We can't move the goto in the middle of a if and a else block, in
// this case we need to move it after the else.
// IsLoop may need to be updated if the label is inside the else, as
// introducing a loop is the only way to ensure the else will be executed.
if (Next(child) is AstBlock elseBlock && elseBlock.Type == AstBlockType.Else)
{
child = elseBlock;
}
block = block.Parent;
block.AddAfter(child, stmt.Goto);
gLevel--;
if (tryInsertElse && child == origin)
{
AstBlock lBlock = ParentBlock(stmt.Label);
IAstNode last = block == lBlock && !stmt.IsLoop ? stmt.Label : null;
AstBlock newBlock = Enclose(block, AstBlockType.Else, null, Next(stmt.Goto), last);
if (newBlock != null)
{
block.Remove(stmt.Goto);
block.AddAfter(newBlock, stmt.Goto);
}
}
}
}
private static bool IndirectlyRelated(AstBlock lBlock, AstBlock rBlock, int lLevel, int rlevel)
{
return(!(lBlock == rBlock || DirectlyRelated(lBlock, rBlock, lLevel, rlevel)));
}