public void VisitBlock(ILAstBlock block)
{
foreach (var statement in block.Statements)
{
statement.AcceptVisitor(this);
}
}
public virtual bool VisitBlock(ILAstBlock block)
{
bool changed = false;
foreach (var statement in block.Statements)
{
changed |= statement.AcceptVisitor(this);
}
return(changed);
}
public string VisitBlock(ILAstBlock block) => "block";
public override bool VisitBlock(ILAstBlock block)
{
// Find all assignments of variables, and count the amount of usages for each variable.
// If the variable is not used it can be removed. If it is only used once, it can be inlined.
bool changed = false;
for (var i = 0; i < block.Statements.Count; i++)
{
// Find assignment statement:
var statement = block.Statements[i];
if (statement is ILAssignmentStatement assignmentStatement && !(assignmentStatement.Variable is ILParameter))
{
bool removeStatement = true;
var usages = assignmentStatement.Variable.UsedBy;
// Count usages.
switch (usages.Count)
{
case 0:
{
if (assignmentStatement.Variable is ILFlagsVariable)
{
removeStatement = false;
}
if (assignmentStatement.Value.HasPotentialSideEffects)
{
// If the value has side effects, it cannot be removed.
removeStatement = false;
assignmentStatement.ReplaceWith(new ILExpressionStatement((ILExpression)assignmentStatement.Value.Remove()));
}
else
{
// Find all variables that are referenced in the statement, and remove them from the
// usage lists.
var embeddedReferences = assignmentStatement.Value.AcceptVisitor(VariableUsageCollector.Instance);
foreach (var reference in embeddedReferences)
{
reference.Variable.UsedBy.Remove(reference);
}
}
break;
}
case 1 when assignmentStatement.Variable.IsVirtual
// We cannot inline into phi nodes.
&& !(usages[0].Parent is ILPhiExpression)
// We also cannot insert phi nodes in arbitrary expressions other than assignments.
&& !(assignmentStatement.Value is ILPhiExpression)
// Finally, we cannot inline expressions with side effects => depend on order of execution.
&& (!assignmentStatement.Value.HasPotentialSideEffects || !HasNoSideEffectsInBetween(assignmentStatement, usages[0])):
{
// Inline the variable's value.
InlineVariable(usages[0], assignmentStatement);
usages.Clear();
break;
}
default:
{
removeStatement = false;
break;
}
}
if (removeStatement)
{
// We applied a transformation, remove the original statement.
block.Statements.RemoveAt(i);
i--;
changed = true;
}
}
}
return(changed);
}
