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Vectorize RegexInterpreter opcode loops for Oneloop, Onerep, Notonerep, and MatchString #124628

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Vectorize RegexInterpreter opcode loops for Oneloop, Onerep, Notonerep, and MatchString #124628

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8e0b5a0
Use vectorized IndexOfAnyExcept for Oneloop/Oneloopatomic in interpreter
danmoseley Feb 20, 2026
22e1768
Use vectorized ContainsAnyExcept for Onerep in interpreter
danmoseley Feb 20, 2026
1fe43b5
Use vectorized Contains for Notonerep in interpreter
danmoseley Feb 20, 2026
6d7b8c6
Use vectorized SequenceEqual for MatchString in interpreter
danmoseley Feb 20, 2026
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89 changes: 64 additions & 25 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 @@ -210,7 +210,6 @@ private char Forwardcharnext(ReadOnlySpan<char> inputSpan)
private bool MatchString(string str, ReadOnlySpan<char> inputSpan)
{
int c = str.Length;
int pos;

if (!_rightToLeft)
{
Expand All @@ -219,7 +218,13 @@ private bool MatchString(string str, ReadOnlySpan<char> inputSpan)
return false;
}

pos = runtextpos + c;
if (!inputSpan.Slice(runtextpos, c).SequenceEqual(str.AsSpan()))
{
return false;
}

runtextpos += c;
return true;
}
else
{
Expand All @@ -228,25 +233,18 @@ private bool MatchString(string str, ReadOnlySpan<char> inputSpan)
return false;
}

pos = runtextpos;
}

while (c != 0)
{
if (str[--c] != inputSpan[--pos])
int pos = runtextpos;
while (c != 0)
{
return false;
if (str[--c] != inputSpan[--pos])
{
return false;
}
}
Comment on lines +237 to 243
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@stephentoub stephentoub Mar 15, 2026

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Can/should this also be a SequenceEqual or EndsWith or equivalent?

}

if (!_rightToLeft)
{
pos += str.Length;
runtextpos = pos;
return true;
}

runtextpos = pos;

return true;
}

private bool MatchRef(int index, int length, ReadOnlySpan<char> inputSpan, bool caseInsensitive)
Expand Down Expand Up @@ -896,12 +894,23 @@ private bool TryMatchAtCurrentPosition(ReadOnlySpan<char> inputSpan)
}

char ch = (char)Operand(0);
while (c-- > 0)
if (!_rightToLeft)
{
if (Forwardcharnext(inputSpan) != ch)
if (inputSpan.Slice(runtextpos, c).ContainsAnyExcept(ch))
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@stephentoub stephentoub Mar 15, 2026

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Is this one actually beneficial? It's pretty rare to have long runs of a single specific character.

{
goto BreakBackward;
}
runtextpos += c;
}
else
{
while (c-- > 0)
{
if (Forwardcharnext(inputSpan) != ch)
{
goto BreakBackward;
}
}
}
}
advance = 2;
Expand All @@ -916,12 +925,23 @@ private bool TryMatchAtCurrentPosition(ReadOnlySpan<char> inputSpan)
}

char ch = (char)Operand(0);
while (c-- > 0)
if (!_rightToLeft)
{
if (Forwardcharnext(inputSpan) == ch)
if (inputSpan.Slice(runtextpos, c).Contains(ch))
{
goto BreakBackward;
}
runtextpos += c;
}
else
{
while (c-- > 0)
{
if (Forwardcharnext(inputSpan) == ch)
{
goto BreakBackward;
}
}
}
}
advance = 2;
Expand Down Expand Up @@ -957,12 +977,31 @@ private bool TryMatchAtCurrentPosition(ReadOnlySpan<char> inputSpan)
char ch = (char)Operand(0);
int i;

for (i = len; i > 0; i--)
if (!_rightToLeft)
{
if (Forwardcharnext(inputSpan) != ch)
// We're left-to-right, so we can employ the vectorized IndexOfAnyExcept
// to search for any character that isn't the target.
i = inputSpan.Slice(runtextpos, len).IndexOfAnyExcept(ch);
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@stephentoub stephentoub Mar 15, 2026

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Same question.

If these onerep/loop/loopatomic actually improve performance on real regexes rather than microbenchmarks targeting these cases, great. Otherwise, though, I'd rather avoid adding more specialized code paths for things that only help with fake scenarios.

if (i == -1)
{
Backwardnext();
break;
runtextpos += len;
i = 0;
}
else
{
runtextpos += i;
i = len - i;
}
}
else
{
for (i = len; i > 0; i--)
{
if (Forwardcharnext(inputSpan) != ch)
{
Backwardnext();
break;
}
}
}

Expand Down
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