Attempt some low hanging perf optimizations in Razor (dotnet#32950)

* Attempt some low hanging perf optimizations

* Use char.IsLetter / char.IsDigit etc to optimize for latin text
* Remove some expensive virtual calls

Author: pranavkm

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Legacy/ParserHelpers.cs

@@ -5,6 +5,7 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using System.Runtime.CompilerServices;
 
 namespace Microsoft.AspNetCore.Razor.Language.Legacy
 {
@@ -55,28 +56,9 @@ public static bool IsIdentifierStart(char value)
 
         public static bool IsIdentifierPart(char value)
         {
-            return IsLetter(value)
-                || IsDecimalDigit(value)
-                || IsConnecting(value)
-                || IsCombining(value)
-                || IsFormatting(value);
-        }
-
-        public static bool IsFormatting(char value)
-        {
-            return CharUnicodeInfo.GetUnicodeCategory(value) == UnicodeCategory.Format;
-        }
-
-        public static bool IsCombining(char value)
-        {
-            var cat = CharUnicodeInfo.GetUnicodeCategory(value);
-
-            return cat == UnicodeCategory.SpacingCombiningMark || cat == UnicodeCategory.NonSpacingMark;
-        }
-
-        public static bool IsConnecting(char value)
-        {
-            return CharUnicodeInfo.GetUnicodeCategory(value) == UnicodeCategory.ConnectorPunctuation;
+            return IsLetter(value) ||
+                IsDecimalDigit(value) ||
+                (CharUnicodeInfo.GetUnicodeCategory(value) is UnicodeCategory.Format or UnicodeCategory.SpacingCombiningMark or UnicodeCategory.NonSpacingMark or UnicodeCategory.ConnectorPunctuation);
         }
 
         public static bool IsWhitespace(char value)
@@ -85,25 +67,14 @@ public static bool IsWhitespace(char value)
                    value == '\f' ||
                    value == '\t' ||
                    value == '\u000B' || // Vertical Tab
-                   CharUnicodeInfo.GetUnicodeCategory(value) == UnicodeCategory.SpaceSeparator;
+                   char.IsSeparator(value);;
         }
 
-        public static bool IsLetter(char value)
-        {
-            var cat = CharUnicodeInfo.GetUnicodeCategory(value);
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static bool IsLetter(char value) => char.IsLetter(value);
 
-            return cat == UnicodeCategory.UppercaseLetter
-                   || cat == UnicodeCategory.LowercaseLetter
-                   || cat == UnicodeCategory.TitlecaseLetter
-                   || cat == UnicodeCategory.ModifierLetter
-                   || cat == UnicodeCategory.OtherLetter
-                   || cat == UnicodeCategory.LetterNumber;
-        }
-
-        public static bool IsDecimalDigit(char value)
-        {
-            return CharUnicodeInfo.GetUnicodeCategory(value) == UnicodeCategory.DecimalDigitNumber;
-        }
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static bool IsDecimalDigit(char value) => char.IsDigit(value);
 
         // From http://dev.w3.org/html5/spec/Overview.html#elements-0
         public static readonly HashSet<string> VoidElements = new HashSet<string>(StringComparer.OrdinalIgnoreCase)

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Legacy/SeekableTextReader.cs

@@ -8,9 +8,10 @@
 
 namespace Microsoft.AspNetCore.Razor.Language.Legacy
 {
-    internal class SeekableTextReader : TextReader, ITextDocument
+    internal sealed class SeekableTextReader : TextReader, ITextDocument
     {
         private readonly RazorSourceDocument _sourceDocument;
+        private readonly string _filePath;
         private int _position;
         private int _current;
         private SourceLocation _location;
@@ -20,12 +21,8 @@ internal class SeekableTextReader : TextReader, ITextDocument
 
         public SeekableTextReader(RazorSourceDocument source)
         {
-            if (source == null)
-            {
-                throw new ArgumentNullException(nameof(source));
-            }
-
             _sourceDocument = source;
+            _filePath = source.FilePath;
             _cachedLineInfo = (new TextSpan(0, _sourceDocument.Lines.GetLineLength(0)), 0);
             UpdateState();
         }
@@ -61,7 +58,7 @@ private void UpdateState()
         {
             if (_cachedLineInfo.Span.Contains(_position))
             {
-                _location = new SourceLocation(_sourceDocument.FilePath, _position, _cachedLineInfo.LineIndex, _position - _cachedLineInfo.Span.Start);
+                _location = new SourceLocation(_filePath, _position, _cachedLineInfo.LineIndex, _position - _cachedLineInfo.Span.Start);
                 _current = _sourceDocument[_location.AbsoluteIndex];
 
                 return;
@@ -79,7 +76,7 @@ private void UpdateState()
                     if (nextLineSpan.Contains(_position))
                     {
                         _cachedLineInfo = (nextLineSpan, nextLineIndex);
-                        _location = new SourceLocation(_sourceDocument.FilePath, _position, nextLineIndex, _position - nextLineSpan.Start);
+                        _location = new SourceLocation(_filePath, _position, nextLineIndex, _position - nextLineSpan.Start);
                         _current = _sourceDocument[_location.AbsoluteIndex];
 
                         return;
@@ -95,7 +92,7 @@ private void UpdateState()
                     if (prevLineSpan.Contains(_position))
                     {
                         _cachedLineInfo = (prevLineSpan, prevLineIndex);
-                        _location = new SourceLocation(_sourceDocument.FilePath, _position, prevLineIndex, _position - prevLineSpan.Start);
+                        _location = new SourceLocation(_filePath, _position, prevLineIndex, _position - prevLineSpan.Start);
                         _current = _sourceDocument[_location.AbsoluteIndex];
 
                         return;
@@ -123,7 +120,7 @@ private void UpdateState()
             }
 
             var lineNumber = _sourceDocument.Lines.Count - 1;
-            _location = new SourceLocation(_sourceDocument.FilePath, Length, lineNumber, _sourceDocument.Lines.GetLineLength(lineNumber));
+            _location = new SourceLocation(_filePath, Length, lineNumber, _sourceDocument.Lines.GetLineLength(lineNumber));
 
             _current = -1;
         }