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Expand RegexNode atomicity test to loops at the end of alternation branches #1769

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Jan 17, 2020
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Expand RegexNode atomicity test to loops at the end of alternation branches #1769

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28 changes: 23 additions & 5 deletions src/libraries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexNode.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -731,11 +731,13 @@ private void ReduceConcatenateWithAutoAtomic()
Debug.Assert((Options & RegexOptions.RightToLeft) == 0);
Debug.Assert(Children is List<RegexNode>);

List<RegexNode> children = (List<RegexNode>)Children;
var children = (List<RegexNode>)Children;
for (int i = 0; i < children.Count - 1; i++)
{
RegexNode node = children[i], subsequent = children[i + 1];
ProcessNode(children[i], children[i + 1]);

static void ProcessNode(RegexNode node, RegexNode subsequent, int maxDepth = 20)
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Nit, might be better to pass in 20 above rather than default it here, so any future calls don't forget to decide what to pass in.

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Same for CanBeMadeAtomic

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Ok. I'll address that subsequently.

{
// Skip down the node past irrelevant nodes. We don't need to
// skip Groups, as they should have already been reduced away.
// If there's a concatenation, we can jump to the last element of it.
Expand All @@ -748,15 +750,30 @@ private void ReduceConcatenateWithAutoAtomic()
// If the node can be changed to atomic based on what comes after it, do so.
switch (node.Type)
{
case Oneloop when CanBeMadeAtomic(node, subsequent):
case Oneloop when CanBeMadeAtomic(node, subsequent, maxDepth - 1):
node.Type = Oneloopatomic;
break;
case Notoneloop when CanBeMadeAtomic(node, subsequent):
case Notoneloop when CanBeMadeAtomic(node, subsequent, maxDepth - 1):
node.Type = Notoneloopatomic;
break;
case Setloop when CanBeMadeAtomic(node, subsequent):
case Setloop when CanBeMadeAtomic(node, subsequent, maxDepth - 1):
node.Type = Setloopatomic;
break;
case Alternate:
// In the case of alternation, we can't change the alternation node itself
// based on what comes after it (at least not with more complicated analysis
// that factors in all branches together), but we can look at each individual
// branch, and analyze ending loops in each branch individually to see if they
// can be made atomic. Then if we do end up backtracking into the alternation,
// we at least won't need to backtrack into that loop.
{
int alternateBranches = node.ChildCount();
for (int b = 0; b < alternateBranches; b++)
{
ProcessNode(node.Child(b), subsequent, maxDepth - 1);
}
}
break;
}

// Determines whether node can be switched to an atomic loop. Subsequent is the node
Expand Down Expand Up @@ -889,6 +906,7 @@ static bool CanBeMadeAtomic(RegexNode node, RegexNode subsequent, int maxDepth =
}
}
}
}
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Aside, I noticed on line 832, this

                    // If this node is a one/notone/setloop, see if it overlaps with its successor in the concatenation.
                    // If it doesn't, then we can upgrade it to being a one/notone/setloopatomic.

maybe should be clarified to say

                    // If this node is a oneloop/notoneloop/setloop, see if it overlaps with its successor in the concatenation.
                    // If it doesn't, then we can upgrade it to being a oneloopatomic/notoneloopatomic/setloopatomic.

since one and notone are node types that are distinct to oneloop/notoneloop.

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Eh, it's everywhere eg

        /// Simple optimization. If an atomic subexpression contains only a one/notone/set loop,
        /// change it to be an atomic one/notone/set loop and remove the atomic node.

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Ok. I can see how it might not be clear; in my head I see the grouping, e.g. as if it were {one/notone/set}loop, but I can clean it up. I'll do so in my next PR.


/// <summary>Computes a min bound on the required length of any string that could possibly match.</summary>
/// <returns>The min computed length. If the result is 0, there is no minimum we can enforce.</returns>
Expand Down
21 changes: 16 additions & 5 deletions src/libraries/System.Text.RegularExpressions/tests/Regex.Groups.Tests.cs
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Expand Up @@ -645,7 +645,7 @@ public static IEnumerable<object[]> Groups_Basic_TestData()
yield return new object[] { null, @"(cat){cat,dog}?", "cat{cat,dog}?", RegexOptions.None, new string[] { "cat{cat,dog}", "cat" } };

// Atomic subexpressions
// Implicitly upgrading oneloop to be atomic
// Implicitly upgrading (or not) oneloop to be atomic
yield return new object[] { null, @"a*", "aaa", RegexOptions.None, new string[] { "aaa" } };
yield return new object[] { null, @"a*b", "aaab", RegexOptions.None, new string[] { "aaab" } };
yield return new object[] { null, @"a*b+", "aaab", RegexOptions.None, new string[] { "aaab" } };
Expand All @@ -669,14 +669,22 @@ public static IEnumerable<object[]> Groups_Basic_TestData()
yield return new object[] { null, @"a*\b", "aaa bbb", RegexOptions.ECMAScript, new string[] { "aaa" } };
yield return new object[] { null, @"@*\B", "@@@", RegexOptions.None, new string[] { "@@@" } };
yield return new object[] { null, @"@*\B", "@@@", RegexOptions.ECMAScript, new string[] { "@@@" } };
// Implicitly upgrading notoneloop to be atomic
yield return new object[] { null, @"(?:abcd*|efgh)i", "efghi", RegexOptions.None, new string[] { "efghi" } };
yield return new object[] { null, @"(?:abcd|efgh*)i", "efgi", RegexOptions.None, new string[] { "efgi" } };
yield return new object[] { null, @"(?:abcd|efghj{2,}|j[klm]o+)i", "efghjjjjji", RegexOptions.None, new string[] { "efghjjjjji" } };
yield return new object[] { null, @"(?:abcd|efghi{2,}|j[klm]o+)i", "efghiii", RegexOptions.None, new string[] { "efghiii" } };
yield return new object[] { null, @"(?:abcd|efghi{2,}|j[klm]o+)i", "efghiiiiiiii", RegexOptions.None, new string[] { "efghiiiiiiii" } };
// Implicitly upgrading (or not) notoneloop to be atomic
yield return new object[] { null, @"[^b]*b", "aaab", RegexOptions.None, new string[] { "aaab" } };
yield return new object[] { null, @"[^b]*b+", "aaab", RegexOptions.None, new string[] { "aaab" } };
yield return new object[] { null, @"[^b]*b+?", "aaab", RegexOptions.None, new string[] { "aaab" } };
yield return new object[] { null, @"[^b]*(?>b+)", "aaab", RegexOptions.None, new string[] { "aaab" } };
yield return new object[] { null, @"[^b]*bac", "aaabac", RegexOptions.None, new string[] { "aaabac" } };
yield return new object[] { null, @"[^b]*", "aaa", RegexOptions.None, new string[] { "aaa" } };
// Implicitly upgrading setloop to be atomic
yield return new object[] { null, @"(?:abc[^b]*|efgh)i", "efghi", RegexOptions.None, new string[] { "efghi" } }; // can't upgrade
yield return new object[] { null, @"(?:abcd|efg[^b]*)b", "efgb", RegexOptions.None, new string[] { "efgb" } };
yield return new object[] { null, @"(?:abcd|efg[^b]*)i", "efgi", RegexOptions.None, new string[] { "efgi" } }; // can't upgrade
// Implicitly upgrading (or not) setloop to be atomic
yield return new object[] { null, @"[ac]*", "aaa", RegexOptions.None, new string[] { "aaa" } };
yield return new object[] { null, @"[ac]*b", "aaab", RegexOptions.None, new string[] { "aaab" } };
yield return new object[] { null, @"[ac]*b+", "aaab", RegexOptions.None, new string[] { "aaab" } };
Expand All @@ -699,14 +707,17 @@ public static IEnumerable<object[]> Groups_Basic_TestData()
yield return new object[] { null, @"[@']*\B", "@@@", RegexOptions.None, new string[] { "@@@" } };
yield return new object[] { null, @"[@']*\B", "@@@", RegexOptions.ECMAScript, new string[] { "@@@" } };
yield return new object[] { null, @".*.", "@@@", RegexOptions.Singleline, new string[] { "@@@" } };
// Implicitly upgrading concat loops to be atomic
yield return new object[] { null, @"(?:abcd|efg[hij]*)h", "efgh", RegexOptions.None, new string[] { "efgh" } }; // can't upgrade
yield return new object[] { null, @"(?:abcd|efg[hij]*)ih", "efgjih", RegexOptions.None, new string[] { "efgjih" } }; // can't upgrade
yield return new object[] { null, @"(?:abcd|efg[hij]*)k", "efgjk", RegexOptions.None, new string[] { "efgjk" } };
// Implicitly upgrading (or not) concat loops to be atomic
yield return new object[] { null, @"(?:[ab]c[de]f)*", "", RegexOptions.None, new string[] { "" } };
yield return new object[] { null, @"(?:[ab]c[de]f)*", "acdf", RegexOptions.None, new string[] { "acdf" } };
yield return new object[] { null, @"(?:[ab]c[de]f)*", "acdfbcef", RegexOptions.None, new string[] { "acdfbcef" } };
yield return new object[] { null, @"(?:[ab]c[de]f)*", "cdfbcef", RegexOptions.None, new string[] { "" } };
yield return new object[] { null, @"(?:[ab]c[de]f)+", "cdfbcef", RegexOptions.None, new string[] { "bcef" } };
yield return new object[] { null, @"(?:[ab]c[de]f)*", "bcefbcdfacfe", RegexOptions.None, new string[] { "bcefbcdf" } };
// Implicitly upgrading nested loops to be atomic
// Implicitly upgrading (or not) nested loops to be atomic
yield return new object[] { null, @"(?:a){3}", "aaaaaaaaa", RegexOptions.None, new string[] { "aaa" } };
yield return new object[] { null, @"(?:a){3}?", "aaaaaaaaa", RegexOptions.None, new string[] { "aaa" } };
yield return new object[] { null, @"(?:a{2}){3}", "aaaaaaaaa", RegexOptions.None, new string[] { "aaaaaa" } };
Expand Down