// GENERATED CODE EXAMPLE: The methods in this region generate
// the for(;;) loop in this example and everything inside it, except
// the calls to Match() which are generated by Visit(TerminalPred).
// The generated code uses "goto" and "match" blocks in some cases
// to avoid code duplication. This occurs when the matching code
// requires multiple statements AND appears more than once in the
// prediction tree. Otherwise, matching is done "inline" during
// prediction. We generate a for(;;) loop for (...)*, and in certain
// cases, we generates a do...while(false) loop for (...)?.
//
// rule Foo @{ (('a'|'A') 'A')* 'a'..'z' 'a'..'z' };
// public void Foo()
// {
// int la0, la1;
// for (;;) {
// la0 = LA(0);
// if (la0 == 'a') {
// la1 = LA(1);
// if (la1 == 'A')
// goto match1;
// else
// break;
// } else if (la0 == 'A')
// goto match1;
// else
// break;
// match1:
// {
// Match('A', 'a');
// Match('A');
// }
// }
// MatchRange('a', 'z');
// MatchRange('a', 'z');
// }
private void GenerateCodeForAlts(Alts alts, Dictionary <int, int> timesUsed, PredictionTree tree)
{
bool needError = LLPG.NeedsErrorBranch(tree, alts);
if (!needError && alts.ErrorBranch != null)
{
LLPG.Output(Warning, alts, "The error branch will not be used because the other alternatives are exhaustive (cover all cases)");
}
bool userDefinedError = needError && !_recognizerMode && alts.ErrorBranch != null && alts.ErrorBranch != DefaultErrorBranch.Value;
// Generate matching code for each arm. the "string" in each pair
// becomes non-null if the matching code for that branch needs to be
// split out (separated) from the prediction tree because it appears
// multiple times in the tree. The string is the goto-label name.
Pair <LNode, string>[] matchingCode = new Pair <LNode, string> [alts.Arms.Count + (userDefinedError ? 1: 0)];
MSet <int> unreachable = new MSet <int>();
int separateCount = 0;
for (int i = 0; i < alts.Arms.Count; i++)
{
if (!timesUsed.ContainsKey(i))
{
unreachable.Add(i);
continue;
}
var codeForThisArm = new WList <LNode>();
VisitWithNewTarget(alts.Arms[i], codeForThisArm);
matchingCode[i].A = F.Braces(codeForThisArm.ToVList());
if (timesUsed[i] > 1 && !SimpleEnoughToRepeat(matchingCode[i].A))
{
separateCount++;
matchingCode[i].B = alts.Arms[i].ChooseGotoLabel()
?? "match" + (i + 1).ToString();
}
}
// Add matching code for the error branch, if present. Note: the
// default error branch, which is produced by IPGCodeGenHelper.
// ErrorBranch() is handled differently: default error code can
// differ at each error point in the prediction tree. Therefore
// we generate it later, on-demand.
if (userDefinedError)
{
int i = alts.Arms.Count;
var errorHandler = new WList <LNode>();
VisitWithNewTarget(alts.ErrorBranch, errorHandler);
matchingCode[i].A = F.Braces(errorHandler.ToVList());
if (timesUsed[ErrorAlt] > 1 && !SimpleEnoughToRepeat(matchingCode[i].A))
{
matchingCode[i].B = "error";
separateCount++;
}
}
// Print unreachability warnings
if (unreachable.Count == 1)
{
LLPG.Output(Warning, alts, string.Format("Branch {{{0}}} is unreachable.", alts.AltName(unreachable.First())));
}
else if (unreachable.Count > 1)
{
LLPG.Output(Warning, alts, string.Format("Branches {{{0}}} are unreachable.", unreachable.Select(i => alts.AltName(i)).Join(", ")));
}
if (!timesUsed.ContainsKey(ExitAlt) && alts.Mode != LoopMode.None)
{
LLPG.Output(Warning, alts, "Infinite loop. The exit branch is unreachable.");
}
Symbol loopType = null;
// Choose a loop type for (...)* or (...)?:
if (alts.Mode == LoopMode.Star)
{
loopType = S.For;
}
else if (alts.Mode == LoopMode.Opt)
{
if (alts.HasErrorBranch(LLPG) || alts.NonExitDefaultArmRequested())
{
loopType = S.DoWhile;
}
}
// If the code for an arm is nontrivial and appears multiple times
// in the prediction table, it will have to be split out into a
// labeled block and reached via "goto". I'd rather just do a goto
// from inside one "if" statement to inside another, but in C#
// (unlike in CIL, and unlike in C) that is prohibited :(
DeduplicateLabels(matchingCode);
var extraMatching = GenerateExtraMatchingCode(matchingCode, separateCount, ref loopType);
if (separateCount != 0)
{
loopType = loopType ?? S.DoWhile;
}
Symbol breakMode = loopType; // used to request a "goto" label in addition to the loop
LNode code = GeneratePredictionTreeCode(tree, matchingCode, ref breakMode);
// Add break/continue between prediction tree and extra matching code,
// if necessary.
if (extraMatching.Count != 0 && CodeGenHelperBase.EndMayBeReachable(code))
{
loopType = loopType ?? S.DoWhile;
extraMatching.Insert(0, GetContinueStmt(loopType));
}
if (!extraMatching.IsEmpty)
{
code = LNode.MergeLists(code, F.Braces(extraMatching), S.Braces);
}
if (loopType == S.For)
{
// (...)* => for (;;) {}
code = F.Call(S.For, F.List(), F.Missing, F.List(), code);
}
else if (loopType == S.DoWhile)
{
// (...)? becomes "do {...} while(false);" IF the exit branch is NOT the default.
// If the exit branch is the default, then no loop and no "break" is needed.
code = F.Call(S.DoWhile, code, F.@false);
}
if (breakMode != loopType && breakMode != null)
{
// Add "stop:" label (plus extra ";" for C# compatibility, in
// case the label ends the block in which it is located.)
var stopLabel = F.Call(S.Label, F.Id(breakMode))
.PlusTrailingTrivia(F.Trivia(S.TriviaRawText, ";"));
code = LNode.MergeLists(code, stopLabel, S.Braces);
}
int oldCount = _target.Count;
_target.SpliceAdd(code, S.Braces);
// Add comment before code
if (LLPG.AddComments)
{
var pos = alts.Basis.Range.Start;
var comment = F.Trivia(S.TriviaSLComment, string.Format(" Line {0}: {1}", pos.Line, alts.ToString()));
if (_target.Count > oldCount)
{
_target[oldCount] = _target[oldCount].PlusAttr(comment);
}
}
}
/// <summary>Extends each level of the prediction tree so that it has
/// total coverage. For example, a typicaly prediction tree might have
/// branches for 'a'..'z' and '0..'9'; this method will add coverage for
/// all other possible inputs. It does this either by adding an error
/// branch, or by extending the set handled by the default branch of
/// each level.</summary>
private void AddElseCases(Alts alts, PredictionTree tree)
{
foreach (var branch in tree.Children)
{
if (branch.Sub.Tree != null)
{
AddElseCases(alts, branch.Sub.Tree);
}
}
if (tree.IsAssertionLevel)
{
tree.Children.Last.AndPreds.Clear();
tree.Children.Last.AndPreds.Add(Set <AndPred> .Empty);
}
else if (!tree.TotalCoverage.ContainsEverything)
{
var rest = tree.TotalCoverage.Inverted();
if (alts.HasErrorBranch(LLPG))
{
tree.Children.Add(new PredictionBranch(rest, new PredictionTreeOrAlt {
Alt = ErrorAlt
}, tree.TotalCoverage));
}
else
{
// No error branch, so use default arm
#if false
// First try: this tends to produce less intuitive code. Neither
// version is objectively better; sometimes this version gives
// faster code and sometimes the other version gives faster code.
int defaultArm = alts.DefaultArmInt();
foreach (PredictionBranch branch in tree.Children)
{
if (branch.Sub.Tree == null && branch.Sub.Alt == defaultArm)
{
branch.Set = branch.Set.Union(rest);
goto done;
}
}
if (alts.DefaultArm != null)
{
tree.Children.Add(new PredictionBranch(rest, defaultArm, tree.TotalCoverage));
}
else
{
tree.Children.Last.Set = tree.Children.Last.Set.Union(rest);
}
done :;
#else
PredictionBranch last = tree.Children.Last;
if (alts.DefaultArm != null && (last.Sub.Tree != null || last.Sub.Alt != alts.DefaultArm.Value))
{
tree.Children.Add(new PredictionBranch(rest, alts.DefaultArm.Value, tree.TotalCoverage));
}
else
{
last.Set = last.Set.Union(rest);
}
#endif
}
}
}
