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Eliminate backtracking in the interpreter for patterns with .* #51508

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17 commits merged into from
Jul 18, 2021
Merged

Eliminate backtracking in the interpreter for patterns with .* #51508

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2511bfa
First cut of look up table for speeding up Go()
Apr 13, 2021
781541c
More efficient .* in RegexInterpreter
Apr 13, 2021
1c7faa0
sq
Apr 19, 2021
7ea6425
Get more debug info
Apr 20, 2021
9c234d4
Remove assert and add unit test
Apr 26, 2021
85b6897
Potential unit test
May 26, 2021
7a404e9
temp
Jun 21, 2021
1949445
Fix a bug
Jun 22, 2021
1564d7a
sq
Jun 22, 2021
7f76e5f
Add extra protection to the backtracking optimization
Jun 22, 2021
ac838ad
Add unit test
Jun 22, 2021
262d5d5
Revert
Jun 30, 2021
aacb00e
RegexCompiler changes
Apr 23, 2021
4f6bdd4
sq
Jul 14, 2021
d8e73cc
Remove debug unit tests
Jul 14, 2021
cb3f3f2
Add a length to the AsSpan call
Jul 14, 2021
3ba7f45
Address RegexCompiler comments and add unit tests
Jul 16, 2021
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140 changes: 123 additions & 17 deletions ...raries/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexCompiler.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,7 @@ internal abstract class RegexCompiler
private static readonly MethodInfo s_spanSliceIntIntMethod = typeof(ReadOnlySpan<char>).GetMethod("Slice", new Type[] { typeof(int), typeof(int) })!;
private static readonly MethodInfo s_spanStartsWith = typeof(MemoryExtensions).GetMethod("StartsWith", new Type[] { typeof(ReadOnlySpan<>).MakeGenericType(Type.MakeGenericMethodParameter(0)), typeof(ReadOnlySpan<>).MakeGenericType(Type.MakeGenericMethodParameter(0)) })!.MakeGenericMethod(typeof(char));
private static readonly MethodInfo s_stringAsSpanMethod = typeof(MemoryExtensions).GetMethod("AsSpan", new Type[] { typeof(string) })!;
private static readonly MethodInfo s_spanLastIndexOfMethod = typeof(MemoryExtensions).GetMethod("LastIndexOf", new Type[] { typeof(ReadOnlySpan<>).MakeGenericType(Type.MakeGenericMethodParameter(0)), typeof(ReadOnlySpan<>).MakeGenericType(Type.MakeGenericMethodParameter(0)) })!.MakeGenericMethod(typeof(char));
private static readonly MethodInfo s_stringAsSpanIntIntMethod = typeof(MemoryExtensions).GetMethod("AsSpan", new Type[] { typeof(string), typeof(int), typeof(int) })!;
private static readonly MethodInfo s_stringGetCharsMethod = typeof(string).GetMethod("get_Chars", new Type[] { typeof(int) })!;
private static readonly MethodInfo s_stringIndexOfCharInt = typeof(string).GetMethod("IndexOf", new Type[] { typeof(char), typeof(int) })!;
Expand All @@ -90,6 +91,7 @@ internal abstract class RegexCompiler
private LocalBuilder? _runstackLocal;
private LocalBuilder? _textInfoLocal; // cached to avoid extraneous TLS hits from CurrentCulture and virtual calls to TextInfo
private LocalBuilder? _loopTimeoutCounterLocal; // timeout counter for setrep and setloop
private LocalBuilder? _maxBacktrackPositionLocal;

protected RegexOptions _options; // options
protected RegexCode? _code; // the RegexCode object
Expand Down Expand Up @@ -891,6 +893,8 @@ private void GenerateForwardSection()
Mvfldloc(s_runtrackposField, _runtrackposLocal!);
Mvfldloc(s_runstackField, _runstackLocal!);
Mvfldloc(s_runstackposField, _runstackposLocal!);
Ldc(-1);
Stloc(_maxBacktrackPositionLocal!);

_backpos = -1;

Expand Down Expand Up @@ -1703,7 +1707,7 @@ protected void GenerateFindFirstChar()
// if (!CharInClass(textSpan[i + 2], prefix[2], "...")) goto returnFalse;
// ...
Debug.Assert(charClassIndex == 0 || charClassIndex == 1);
for ( ; charClassIndex < _leadingCharClasses.Length; charClassIndex++)
for (; charClassIndex < _leadingCharClasses.Length; charClassIndex++)
{
Debug.Assert(needLoop);
Ldloca(textSpanLocal);
Expand Down Expand Up @@ -3308,6 +3312,7 @@ protected void GenerateGo()
}
_runtextbegLocal = DeclareInt32();
_runtextendLocal = DeclareInt32();
_maxBacktrackPositionLocal = DeclareInt32();

InitializeCultureForGoIfNecessary();

Expand Down Expand Up @@ -4256,7 +4261,61 @@ private void GenerateOneCode()
//: break Backward;
{
string str = _strings![Operand(0)];
Label multiCode = DefineLabel();
if (!IsRightToLeft())
{
// if (runtextend - runtextpos < c)
Ldloc(_runtextendLocal!);
Ldloc(_runtextposLocal!);
Sub();
Ldc(str.Length);
BgeFar(multiCode);
// if (!caseInsensitive && _maxBacktrackPosition != -1 && runtextpos > _maxBacktrackPosition)
if (!IsCaseInsensitive())
{
Ldloc(_maxBacktrackPositionLocal!);
Ldc(-1);
BeqFar(_backtrack);
Ldloc(_runtextposLocal!);
Ldloc(_maxBacktrackPositionLocal!);
BleFar(_backtrack);
// runtextpos = _maxBacktrackPosition;
Ldloc(_maxBacktrackPositionLocal!);
Stloc(_runtextposLocal!);
// ReadOnlySpan<char> runtextSpan = runtext.AsSpan(_maxBacktrackPosition, runtextend - _maxBacktractPosition);
Ldloc(_runtextLocal!);
Ldloc(_maxBacktrackPositionLocal!);
Ldloc(_runtextendLocal!);
Ldloc(_maxBacktrackPositionLocal!);
Sub();
using (RentedLocalBuilder runtextSpanLocal = RentReadOnlySpanCharLocal())
{
Call(s_stringAsSpanIntIntMethod);
Stloc(runtextSpanLocal);
using (RentedLocalBuilder lastIndexOfLocal = RentInt32Local())
{
// int lastIndexOf = runtextSpan.LastIndexOf(str.AsSpan());
Ldloc(runtextSpanLocal);
Ldstr(str);
Call(s_stringAsSpanMethod);
Call(s_spanLastIndexOfMethod);
Stloc(lastIndexOfLocal);
// if (lastIndexOf > -1)
Ldloc(lastIndexOfLocal);
Ldc(-1);
BleFar(_backtrack);
// runtextpos = lastIndexOf + _maxBacktrackPosition;
Ldloc(lastIndexOfLocal);
Ldloc(_maxBacktrackPositionLocal!);
Add();
Stloc(_runtextposLocal!);
BrFar(_backtrack);
}
}
}
}

MarkLabel(multiCode);
Ldc(str.Length);
Ldloc(_runtextendLocal!);
Ldloc(_runtextposLocal!);
Expand Down Expand Up @@ -4596,6 +4655,9 @@ private void GenerateOneCode()

using RentedLocalBuilder lenLocal = RentInt32Local();
using RentedLocalBuilder iLocal = RentInt32Local();
using RentedLocalBuilder tempMaxBacktrackPositionLocal = RentInt32Local();
Ldloc(_runtextposLocal!);
Stloc(tempMaxBacktrackPositionLocal);

if (!IsRightToLeft())
{
Expand Down Expand Up @@ -4845,6 +4907,12 @@ private void GenerateOneCode()
DoPush();

Track();
// if (_operator == RegexCode.Notoneloop) maxBacktrackPosition = tempMaxBacktrackPosition
if (_regexopcode == RegexCode.Notoneloop)
{
Ldloc(tempMaxBacktrackPositionLocal);
Stloc(_maxBacktrackPositionLocal!);
}
}
break;
}
Expand All @@ -4868,28 +4936,66 @@ private void GenerateOneCode()
//: if (i > 0)
//: Track(i - 1, pos - 1);
//: Advance(2);
PopTrack();
Stloc(_runtextposLocal!);
Label noBacktrackPositionBranch = DefineLabel();
PopTrack();
using (RentedLocalBuilder posLocal = RentInt32Local())
{
Stloc(posLocal);
Ldloc(posLocal);
Ldc(0);
BleFar(AdvanceLabel());
PopTrack();
using (RentedLocalBuilder iBacktrackLocal = RentInt32Local())
{
Stloc(iBacktrackLocal);
// if (!caseInsensitive && maxBacktrackPosition != -1 && pos > maxBacktrackPosition && runtextpos < pos && _operator == (RegexCode.Notoneloop | RegexCode.Back) && !_rightToLeft)
if (!IsCaseInsensitive() && _regexopcode == (RegexCode.Notoneloop | RegexCode.Back) && !IsRightToLeft())
{
Ldloc(_maxBacktrackPositionLocal!);
Ldc(-1);
Beq(noBacktrackPositionBranch);
Ldloc(posLocal);
Ldloc(_maxBacktrackPositionLocal!);
Ble(noBacktrackPositionBranch);
Ldloc(_runtextposLocal!);
Ldloc(posLocal);
Bge(noBacktrackPositionBranch);
/*
int difference = pos - maxBacktrackPosition;
pos = runtextpos;
i -= difference;
maxBacktrackPosition = -1;
*/
// int difference = pos - maxBacktrackPosition;
Ldloc(iBacktrackLocal);
Ldloc(posLocal);
Ldloc(_maxBacktrackPositionLocal!);
Sub();
Sub();
Stloc(iBacktrackLocal);
Ldloc(_runtextposLocal!);
Stloc(posLocal);
Ldc(-1);
Stloc(_maxBacktrackPositionLocal!);
}

MarkLabel(noBacktrackPositionBranch);
Ldloc(posLocal);
Stloc(_runtextposLocal!);
Ldloc(iBacktrackLocal);
Ldc(0);
BleFar(AdvanceLabel());
ReadyPushTrack();
Ldloc(iBacktrackLocal);
}
Ldc(1);
Sub();
DoPush();
ReadyPushTrack();
Ldloc(posLocal);
Ldloc(_runtextposLocal!);
Ldc(1);
Sub(IsRightToLeft());
DoPush();
Trackagain();
Advance();
}
Ldc(1);
Sub();
DoPush();
ReadyPushTrack();
Ldloc(_runtextposLocal!);
Ldc(1);
Sub(IsRightToLeft());
DoPush();
Trackagain();
Advance();
break;

case RegexCode.Onelazy:
Expand Down
27 changes: 27 additions & 0 deletions ...ies/System.Text.RegularExpressions/src/System/Text/RegularExpressions/RegexInterpreter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ internal sealed class RegexInterpreter : RegexRunner
private int _codepos;
private bool _rightToLeft;
private bool _caseInsensitive;
private int _maxBacktrackPosition = -1;

public RegexInterpreter(RegexCode code, CultureInfo culture)
{
Expand Down Expand Up @@ -223,6 +224,20 @@ private bool MatchString(string str)
{
if (runtextend - runtextpos < c)
{
// If MatchString was called after a greedy op such as a .*, we would have zipped runtextpos to the end without really examining any characters. Reset to maxBacktrackPos here as an optimization
if (!_caseInsensitive && _maxBacktrackPosition != -1 && runtextpos > _maxBacktrackPosition)
{
// If lastIndexOf is -1, we backtrack to the max extent possible.
runtextpos = _maxBacktrackPosition;
ReadOnlySpan<char> runtextSpan = runtext.AsSpan(_maxBacktrackPosition, runtextend - _maxBacktrackPosition);
int lastIndexOf = runtextSpan.LastIndexOf(str);
if (lastIndexOf > -1)
{
// Found the next position to match. Move runtextpos here
runtextpos = _maxBacktrackPosition + lastIndexOf;
}
}

return false;
}

Expand Down Expand Up @@ -1185,6 +1200,7 @@ protected override void Go()
int len = Math.Min(Operand(1), Forwardchars());
char ch = (char)Operand(0);
int i;
int tempMaxBacktrackPosition = runtextpos;

if (!_rightToLeft && !_caseInsensitive)
{
Expand Down Expand Up @@ -1217,6 +1233,7 @@ protected override void Go()
if (len > i && _operator == RegexCode.Notoneloop)
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I wonder whether this should also happen for Notoneloopatomic.

{
TrackPush(len - i - 1, runtextpos - Bump());
_maxBacktrackPosition = tempMaxBacktrackPosition;
}
}
advance = 2;
Expand Down Expand Up @@ -1261,6 +1278,16 @@ protected override void Go()
{
int i = TrackPeek();
int pos = TrackPeek(1);
if (!_caseInsensitive && _maxBacktrackPosition != -1 && pos > _maxBacktrackPosition && runtextpos < pos && _operator == (RegexCode.Notoneloop | RegexCode.Back) && !_rightToLeft)
{
// The Multi node has bumped us along already
int difference = pos - _maxBacktrackPosition;
Debug.Assert(difference > 0);
pos = runtextpos;
i -= difference;
// We shouldn't be backtracking anymore.
_maxBacktrackPosition = -1;
}
runtextpos = pos;
if (i > 0)
{
Expand Down
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