private bool TryOptimizeCompareWithZero(ILCompilationUnit unit, ILFlagsVariable fl, ILVariableExpression flUsage)
{
if (fl.ImplicitAssignments.Count != 1)
{
return(false);
}
var flAssignment = fl.ImplicitAssignments.First();
MatchResult match;
if ((match = ComparePattern.Match(flAssignment)).Success) // (cmp(a, b); equals(FL, 0)) <=> (a == b)
{
return(TryOptimizeToEquals(unit, fl, flUsage, flAssignment, match));
}
if ((match = BigRelationalPattern.Match(flAssignment)).Success)
{
return(TryOptimizeToLessThan(unit, fl, flUsage, flAssignment, match));
}
if ((match = AndRegistersPattern.Match(flAssignment)).Success)
{
return(TryOptimizeToGreaterThan(unit, fl, flUsage, flAssignment, match));
}
return(false);
}
private bool TryOptimizeToEquals(
ILCompilationUnit unit,
ILFlagsVariable fl,
ILVariableExpression flUsage,
ILExpression flAssignment,
MatchResult match)
{
// Replace FL operation with the new comparison operation.
ILOpCode opcode;
switch (((ILInstructionExpression)flAssignment).OpCode.Code)
{
case ILCode.CMP:
opcode = ILOpCodes.__EQUALS_OBJECT;
break;
case ILCode.CMP_R32:
opcode = ILOpCodes.__EQUALS_R32;
break;
case ILCode.CMP_R64:
opcode = ILOpCodes.__EQUALS_R64;
break;
case ILCode.CMP_DWORD:
opcode = ILOpCodes.__EQUALS_DWORD;
break;
case ILCode.CMP_QWORD:
opcode = ILOpCodes.__EQUALS_QWORD;
break;
default:
return(false);
}
// Introduce new variable for storing the result of the comparison.
var resultVar = unit.GetOrCreateVariable($"simplified_{fl.Name}");
resultVar.VariableType = VMType.Dword;
var assignment = new ILAssignmentStatement(resultVar,
new ILInstructionExpression(-1, opcode, null, VMType.Dword)
{
Arguments =
{
(ILExpression)match.Captures["left"][0].Remove(),
(ILExpression)match.Captures["right"][0].Remove()
}
});
fl.ImplicitAssignments.Remove(flAssignment);
flAssignment.Parent.ReplaceWith(assignment);
// Replace FL reference with new variable.
flUsage.Variable = null;
flUsage.Parent.Parent.ReplaceWith(new ILVariableExpression(resultVar));
return(true);
}
private bool TryOptimizeToGreaterThan(
ILCompilationUnit unit,
ILFlagsVariable fl,
ILVariableExpression flUsage,
ILExpression flAssignment,
MatchResult match)
{
var root = flUsage.Parent?.Parent?.Parent?.Parent;
var relationalMatch = BigRelationalPattern.Match(root);
if (!relationalMatch.Success || !ValidateRelationalMatch(relationalMatch, out var variable))
{
return(false);
}
if (!ValidateRemainingRelationalNodes(match, variable, VMFlags.OVERFLOW | VMFlags.SIGN | VMFlags.ZERO,
out var varAssignment, out var flAssignment2, out var cmpMatch))
{
return(false);
}
// We have a match! Decide which opcode to use based on the original comparison that was made.
ILOpCode opcode;
switch (((ILInstructionExpression)flAssignment2).OpCode.Code)
{
case ILCode.CMP_R32:
opcode = ILOpCodes.__GT_R64;
break;
case ILCode.CMP_R64:
opcode = ILOpCodes.__GT_R64;
break;
case ILCode.CMP_DWORD:
opcode = ILOpCodes.__GT_DWORD;
break;
case ILCode.CMP_QWORD:
opcode = ILOpCodes.__GT_QWORD;
break;
default:
return(false);
}
// Introduce new variable for storing the result of the comparison.
var resultVar = unit.GetOrCreateVariable("simplified_" + fl.Name);
resultVar.VariableType = VMType.Dword;
var newAssignment = new ILAssignmentStatement(resultVar,
new ILInstructionExpression(-1, opcode, null, VMType.Dword)
{
Arguments =
{
(ILExpression)cmpMatch.Captures["left"][0].Remove(),
(ILExpression)cmpMatch.Captures["right"][0].Remove()
}
});
// Remove var0 assignment.
varAssignment.Variable = null;
varAssignment.Remove();
// Remove comparison.
flAssignment2.Parent.Remove();
// Clear references to variables.
var referencesToRemove = new List <ILVariableExpression>();
referencesToRemove.AddRange(root.AcceptVisitor(VariableUsageCollector.Instance));
referencesToRemove.AddRange(flAssignment.AcceptVisitor(VariableUsageCollector.Instance));
referencesToRemove.AddRange(varAssignment.AcceptVisitor(VariableUsageCollector.Instance));
referencesToRemove.AddRange(flAssignment2.AcceptVisitor(VariableUsageCollector.Instance));
foreach (var reference in referencesToRemove)
{
reference.Variable = null;
reference.Remove();
}
// Replace assignment and use of FL with new variable.
flAssignment.FlagsVariable = null;
flAssignment.Parent.ReplaceWith(newAssignment);
root.ReplaceWith(new ILVariableExpression(resultVar));
return(true);
}
private bool TryOptimizeFlagComparison(ILCompilationUnit unit, ILVariableExpression flagUsage, ILFlagsVariable fl, VMFlags flags)
{
// TODO: support other flag combinations.
bool changed = false;
switch (flags)
{
case VMFlags.ZERO:
changed |= TryOptimizeCompareWithZero(unit, fl, flagUsage);
break;
}
return(changed);
}
