Tweak Invariant IndexOf logic (#108728)

Co-authored-by: Miha Zupan <[email protected]>

Author: github-actions[bot]

src/libraries/System.Private.CoreLib/src/System/Globalization/CompareInfo.Icu.cs

@@ -130,14 +130,12 @@ private unsafe int IndexOfOrdinalIgnoreCaseHelper(ReadOnlySpan<char> source, Rea
                 }
 
                 int startIndex, endIndex, jump;
-                ReadOnlySpan<char> remainingSource;
                 if (fromBeginning)
                 {
                     // Left to right, from zero to last possible index in the source string.
                     // Incrementing by one after each iteration. Stop condition is last possible index plus 1.
                     startIndex = 0;
                     endIndex = source.Length - target.Length + 1;
-                    remainingSource = source.Slice(endIndex);
                     jump = 1;
                 }
                 else
@@ -146,7 +144,6 @@ private unsafe int IndexOfOrdinalIgnoreCaseHelper(ReadOnlySpan<char> source, Rea
                     // Decrementing by one after each iteration. Stop condition is last possible index minus 1.
                     startIndex = source.Length - target.Length;
                     endIndex = -1;
-                    remainingSource = source.Slice(0, startIndex);
                     jump = -1;
                 }
 
@@ -196,6 +193,10 @@ private unsafe int IndexOfOrdinalIgnoreCaseHelper(ReadOnlySpan<char> source, Rea
                 }
 
                 // Before we return -1, check if the remaining source contains any special or non-Ascii characters.
+                ReadOnlySpan<char> remainingSource = fromBeginning
+                    ? source.Slice(endIndex)
+                    : source.Slice(0, startIndex);
+
                 if (remainingSource.ContainsAnyExcept(s_nonSpecialAsciiChars))
                 {
                     goto InteropCall;
@@ -255,14 +256,12 @@ private unsafe int IndexOfOrdinalHelper(ReadOnlySpan<char> source, ReadOnlySpan<
                 }
 
                 int startIndex, endIndex, jump;
-                ReadOnlySpan<char> remainingSource;
                 if (fromBeginning)
                 {
                     // Left to right, from zero to last possible index in the source string.
                     // Incrementing by one after each iteration. Stop condition is last possible index plus 1.
                     startIndex = 0;
                     endIndex = source.Length - target.Length + 1;
-                    remainingSource = source.Slice(endIndex);
                     jump = 1;
                 }
                 else
@@ -271,7 +270,6 @@ private unsafe int IndexOfOrdinalHelper(ReadOnlySpan<char> source, ReadOnlySpan<
                     // Decrementing by one after each iteration. Stop condition is last possible index minus 1.
                     startIndex = source.Length - target.Length;
                     endIndex = -1;
-                    remainingSource = source.Slice(0, startIndex);
                     jump = -1;
                 }
 
@@ -309,12 +307,6 @@ private unsafe int IndexOfOrdinalHelper(ReadOnlySpan<char> source, ReadOnlySpan<
                 Next: ;
                 }
 
-                // Before we return -1, check if the remaining source contains any special or non-Ascii characters.
-                if (remainingSource.ContainsAnyExcept(s_nonSpecialAsciiChars))
-                {
-                    goto InteropCall;
-                }
-
                 return -1;
 
             InteropCall: