diff --git a/src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Helper/Base64DecoderHelper.cs b/src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Helper/Base64DecoderHelper.cs
index 0c0acd6a933d4..747927db98c35 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Helper/Base64DecoderHelper.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Buffers/Text/Base64Helper/Base64DecoderHelper.cs
@@ -1331,7 +1331,7 @@ public bool TryDecode256Core(
                 Vector256<sbyte> hi = Avx2.Shuffle(lutHigh, hiNibbles);
                 Vector256<sbyte> lo = Avx2.Shuffle(lutLow, loNibbles);
 
-                if (!Avx.TestZ(lo, hi))
+                if ((lo & hi) != Vector256<sbyte>.Zero)
                 {
                     result = default;
                     return false;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Utility.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Utility.cs
index f8f12c2c321ce..510c06d0311c5 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Utility.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Ascii.Utility.cs
@@ -1501,10 +1501,10 @@ private static bool VectorContainsNonAsciiChar(Vector128<byte> asciiVector)
         {
             // max ASCII character is 0b_0111_1111, so the most significant bit (0x80) tells whether it contains non ascii
 
-            // prefer architecture specific intrinsic as they offer better perf
+            // For performance, prefer architecture specific implementation
             if (Sse41.IsSupported)
             {
-                return !Sse41.TestZ(asciiVector, Vector128.Create((byte)0x80));
+                return (asciiVector & Vector128.Create((byte)0x80)) != Vector128<byte>.Zero;
             }
             else if (AdvSimd.Arm64.IsSupported)
             {
@@ -1520,23 +1520,21 @@ private static bool VectorContainsNonAsciiChar(Vector128<byte> asciiVector)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static bool VectorContainsNonAsciiChar(Vector128<ushort> utf16Vector)
         {
-            // prefer architecture specific intrinsic as they offer better perf
-            if (Sse2.IsSupported)
+            // For performance, prefer architecture specific implementation
+            if (Sse41.IsSupported)
             {
-                if (Sse41.IsSupported)
-                {
-                    Vector128<ushort> asciiMaskForTestZ = Vector128.Create((ushort)0xFF80);
-                    // If a non-ASCII bit is set in any WORD of the vector, we have seen non-ASCII data.
-                    return !Sse41.TestZ(utf16Vector.AsInt16(), asciiMaskForTestZ.AsInt16());
-                }
-                else
-                {
-                    Vector128<ushort> asciiMaskForAddSaturate = Vector128.Create((ushort)0x7F80);
-                    // The operation below forces the 0x8000 bit of each WORD to be set iff the WORD element
-                    // has value >= 0x0800 (non-ASCII). Then we'll treat the vector as a BYTE vector in order
-                    // to extract the mask. Reminder: the 0x0080 bit of each WORD should be ignored.
-                    return (Sse2.MoveMask(Sse2.AddSaturate(utf16Vector, asciiMaskForAddSaturate).AsByte()) & 0b_1010_1010_1010_1010) != 0;
-                }
+                const ushort asciiMask = ushort.MaxValue - 127; // 0xFF80
+                Vector128<ushort> zeroIsAscii = utf16Vector & Vector128.Create(asciiMask);
+                // If a non-ASCII bit is set in any WORD of the vector, we have seen non-ASCII data.
+                return zeroIsAscii != Vector128<ushort>.Zero;
+            }
+            else if (Sse2.IsSupported)
+            {
+                Vector128<ushort> asciiMaskForAddSaturate = Vector128.Create((ushort)0x7F80);
+                // The operation below forces the 0x8000 bit of each WORD to be set iff the WORD element
+                // has value >= 0x0800 (non-ASCII). Then we'll treat the vector as a BYTE vector in order
+                // to extract the mask. Reminder: the 0x0080 bit of each WORD should be ignored.
+                return (Sse2.MoveMask(Sse2.AddSaturate(utf16Vector, asciiMaskForAddSaturate).AsByte()) & 0b_1010_1010_1010_1010) != 0;
             }
             else if (AdvSimd.Arm64.IsSupported)
             {
@@ -1557,18 +1555,10 @@ internal static bool VectorContainsNonAsciiChar(Vector128<ushort> utf16Vector)
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         internal static bool VectorContainsNonAsciiChar(Vector256<ushort> utf16Vector)
         {
-            if (Avx.IsSupported)
-            {
-                Vector256<ushort> asciiMaskForTestZ = Vector256.Create((ushort)0xFF80);
-                return !Avx.TestZ(utf16Vector.AsInt16(), asciiMaskForTestZ.AsInt16());
-            }
-            else
-            {
-                const ushort asciiMask = ushort.MaxValue - 127; // 0xFF80
-                Vector256<ushort> zeroIsAscii = utf16Vector & Vector256.Create(asciiMask);
-                // If a non-ASCII bit is set in any WORD of the vector, we have seen non-ASCII data.
-                return zeroIsAscii != Vector256<ushort>.Zero;
-            }
+            const ushort asciiMask = ushort.MaxValue - 127; // 0xFF80
+            Vector256<ushort> zeroIsAscii = utf16Vector & Vector256.Create(asciiMask);
+            // If a non-ASCII bit is set in any WORD of the vector, we have seen non-ASCII data.
+            return zeroIsAscii != Vector256<ushort>.Zero;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -1601,14 +1591,13 @@ private static bool AllCharsInVectorAreAscii<T>(Vector128<T> vector)
             if (typeof(T) == typeof(byte))
             {
                 return
-                    Sse41.IsSupported ? Sse41.TestZ(vector.AsByte(), Vector128.Create((byte)0x80)) :
+                    Sse41.IsSupported ? (vector.AsByte() & Vector128.Create((byte)0x80)) == Vector128<byte>.Zero :
                     AdvSimd.Arm64.IsSupported ? AllBytesInUInt64AreAscii(AdvSimd.Arm64.MaxPairwise(vector.AsByte(), vector.AsByte()).AsUInt64().ToScalar()) :
                     vector.AsByte().ExtractMostSignificantBits() == 0;
             }
             else
             {
                 return
-                    Sse41.IsSupported ? Sse41.TestZ(vector.AsUInt16(), Vector128.Create((ushort)0xFF80)) :
                     AdvSimd.Arm64.IsSupported ? AllCharsInUInt64AreAscii(AdvSimd.Arm64.MaxPairwise(vector.AsUInt16(), vector.AsUInt16()).AsUInt64().ToScalar()) :
                     (vector.AsUInt16() & Vector128.Create((ushort)0xFF80)) == Vector128<ushort>.Zero;
             }
@@ -1624,14 +1613,12 @@ private static bool AllCharsInVectorAreAscii<T>(Vector256<T> vector)
             if (typeof(T) == typeof(byte))
             {
                 return
-                    Avx.IsSupported ? Avx.TestZ(vector.AsByte(), Vector256.Create((byte)0x80)) :
+                    Avx.IsSupported ? (vector.AsByte() & Vector256.Create((byte)0x80)) == Vector256<byte>.Zero:
                     vector.AsByte().ExtractMostSignificantBits() == 0;
             }
             else
             {
-                return
-                    Avx.IsSupported ? Avx.TestZ(vector.AsUInt16(), Vector256.Create((ushort)0xFF80)) :
-                    (vector.AsUInt16() & Vector256.Create((ushort)0xFF80)) == Vector256<ushort>.Zero;
+                return (vector.AsUInt16() & Vector256.Create((ushort)0xFF80)) == Vector256<ushort>.Zero;
             }
         }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Latin1Utility.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Latin1Utility.cs
index e8cd792243e31..14d336ace4e48 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Latin1Utility.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Latin1Utility.cs
@@ -267,7 +267,7 @@ private static unsafe nuint GetIndexOfFirstNonLatin1Char_Sse2(char* pBuffer, nui
                     {
                         // If a non-Latin-1 bit is set in any WORD of the combined vector, we have seen non-Latin-1 data.
                         // Jump to the non-Latin-1 handler to figure out which particular vector contained non-Latin-1 data.
-                        if (!Sse41.TestZ(combinedVector, latin1MaskForTestZ))
+                        if ((combinedVector & latin1MaskForTestZ) != Vector128<ushort>.Zero)
                         {
                             goto FoundNonLatin1DataInFirstOrSecondVector;
                         }
@@ -312,7 +312,7 @@ private static unsafe nuint GetIndexOfFirstNonLatin1Char_Sse2(char* pBuffer, nui
             {
                 // If a non-Latin-1 bit is set in any WORD of the combined vector, we have seen non-Latin-1 data.
                 // Jump to the non-Latin-1 handler to figure out which particular vector contained non-Latin-1 data.
-                if (!Sse41.TestZ(firstVector, latin1MaskForTestZ))
+                if ((firstVector & latin1MaskForTestZ) != Vector128<ushort>.Zero)
                 {
                     goto FoundNonLatin1DataInFirstVector;
                 }
@@ -347,7 +347,7 @@ private static unsafe nuint GetIndexOfFirstNonLatin1Char_Sse2(char* pBuffer, nui
                 {
                     // If a non-Latin-1 bit is set in any WORD of the combined vector, we have seen non-Latin-1 data.
                     // Jump to the non-Latin-1 handler to figure out which particular vector contained non-Latin-1 data.
-                    if (!Sse41.TestZ(firstVector, latin1MaskForTestZ))
+                    if ((firstVector & latin1MaskForTestZ) != Vector128<ushort>.Zero)
                     {
                         goto FoundNonLatin1DataInFirstVector;
                     }
@@ -381,7 +381,7 @@ private static unsafe nuint GetIndexOfFirstNonLatin1Char_Sse2(char* pBuffer, nui
             if (Sse41.IsSupported)
 #pragma warning restore IntrinsicsInSystemPrivateCoreLibAttributeNotSpecificEnough
             {
-                if (!Sse41.TestZ(firstVector, latin1MaskForTestZ))
+                if ((firstVector & latin1MaskForTestZ) != Vector128<ushort>.Zero)
                 {
                     goto FoundNonLatin1DataInFirstVector;
                 }
@@ -795,7 +795,7 @@ private static unsafe nuint NarrowUtf16ToLatin1_Sse2(char* pUtf16Buffer, byte* p
             if (Sse41.IsSupported)
 #pragma warning restore IntrinsicsInSystemPrivateCoreLibAttributeNotSpecificEnough
             {
-                if (!Sse41.TestZ(utf16VectorFirst, latin1MaskForTestZ))
+                if ((utf16VectorFirst & latin1MaskForTestZ) != Vector128<short>.Zero)
                 {
                     return 0;
                 }
@@ -837,7 +837,7 @@ private static unsafe nuint NarrowUtf16ToLatin1_Sse2(char* pUtf16Buffer, byte* p
                 if (Sse41.IsSupported)
 #pragma warning restore IntrinsicsInSystemPrivateCoreLibAttributeNotSpecificEnough
                 {
-                    if (!Sse41.TestZ(utf16VectorFirst, latin1MaskForTestZ))
+                    if ((utf16VectorFirst & latin1MaskForTestZ) != Vector128<short>.Zero)
                     {
                         goto Finish;
                     }
@@ -878,7 +878,7 @@ private static unsafe nuint NarrowUtf16ToLatin1_Sse2(char* pUtf16Buffer, byte* p
                 if (Sse41.IsSupported)
 #pragma warning restore IntrinsicsInSystemPrivateCoreLibAttributeNotSpecificEnough
                 {
-                    if (!Sse41.TestZ(combinedVector, latin1MaskForTestZ))
+                    if ((combinedVector & latin1MaskForTestZ) != Vector128<short>.Zero)
                     {
                         goto FoundNonLatin1DataInLoop;
                     }
@@ -914,7 +914,7 @@ private static unsafe nuint NarrowUtf16ToLatin1_Sse2(char* pUtf16Buffer, byte* p
             if (Sse41.IsSupported)
 #pragma warning restore IntrinsicsInSystemPrivateCoreLibAttributeNotSpecificEnough
             {
-                if (!Sse41.TestZ(utf16VectorFirst, latin1MaskForTestZ))
+                if ((utf16VectorFirst & latin1MaskForTestZ) != Vector128<short>.Zero)
                 {
                     goto Finish; // found non-Latin-1 data
                 }
diff --git a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
index e700f8ad48359..2164520428988 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Text/Unicode/Utf8Utility.Transcoding.cs
@@ -968,7 +968,7 @@ public static OperationStatus TranscodeToUtf8(char* pInputBuffer, int inputLengt
                             }
                             else if (Sse41.IsSupported)
                             {
-                                if (!Sse41.TestZ(utf16Data, nonAsciiUtf16DataMask))
+                                if ((utf16Data & nonAsciiUtf16DataMask) != Vector128<short>.Zero)
                                 {
                                     goto LoopTerminatedDueToNonAsciiDataInVectorLocal;
                                 }