diff --git a/eng/SourceBuildPrebuiltBaseline.xml b/eng/SourceBuildPrebuiltBaseline.xml
index 4185d755fa6129..296c7a7f4b81df 100644
--- a/eng/SourceBuildPrebuiltBaseline.xml
+++ b/eng/SourceBuildPrebuiltBaseline.xml
@@ -35,5 +35,18 @@
     <UsagePattern IdentityGlob="System.IO.Pipelines/7.0.0" />
     <UsagePattern IdentityGlob="System.IO.Pipelines/8.0.*" />
     <UsagePattern IdentityGlob="System.Security.Cryptography.Pkcs/5.0.0" />
+
+    <!-- Dependencies of Roslyn, replaced with live packages during full source build
+         https://github.com/dotnet/runtime/pull/112937#discussion_r2022951143 -->
+    <UsagePattern IdentityGlob="Microsoft.Bcl.AsyncInterfaces/9.0.0" />
+    <UsagePattern IdentityGlob="System.Collections.Immutable/9.0.0" />
+    <UsagePattern IdentityGlob="System.Composition/9.0.0" />
+    <UsagePattern IdentityGlob="System.Composition.AttributedModel/9.0.0" />
+    <UsagePattern IdentityGlob="System.Composition.Convention/9.0.0" />
+    <UsagePattern IdentityGlob="System.Composition.Hosting/9.0.0" />
+    <UsagePattern IdentityGlob="System.Composition.Runtime/9.0.0" />
+    <UsagePattern IdentityGlob="System.Composition.TypedParts/9.0.0" />
+    <UsagePattern IdentityGlob="System.IO.Pipelines/9.0.0" />
+    <UsagePattern IdentityGlob="System.Reflection.Metadata/9.0.0" />
   </IgnorePatterns>
 </UsageData>
diff --git a/eng/Version.Details.xml b/eng/Version.Details.xml
index 12f8259f9344cf..4423c3fbb40e8e 100644
--- a/eng/Version.Details.xml
+++ b/eng/Version.Details.xml
@@ -360,30 +360,30 @@
       <Uri>https://github.com/dotnet/runtime-assets</Uri>
       <Sha>91ea918f8fb26ec1d290283e5c5eeb1b003113da</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.Net.Compilers.Toolset" Version="4.12.0-3.25569.8">
+    <Dependency Name="Microsoft.Net.Compilers.Toolset" Version="4.14.0-3.25570.7">
       <Uri>https://github.com/dotnet/roslyn</Uri>
-      <Sha>dc344ef24932dcd53cdd24c15364a5996bc6a675</Sha>
+      <Sha>8cafac4760a78176ef0e167bea66b97b65437930</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.CodeAnalysis" Version="4.12.0-3.25569.8">
+    <Dependency Name="Microsoft.CodeAnalysis" Version="4.14.0-3.25570.7">
       <Uri>https://github.com/dotnet/roslyn</Uri>
-      <Sha>dc344ef24932dcd53cdd24c15364a5996bc6a675</Sha>
+      <Sha>8cafac4760a78176ef0e167bea66b97b65437930</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.CodeAnalysis.CSharp" Version="4.12.0-3.25569.8">
+    <Dependency Name="Microsoft.CodeAnalysis.CSharp" Version="4.14.0-3.25570.7">
       <Uri>https://github.com/dotnet/roslyn</Uri>
-      <Sha>dc344ef24932dcd53cdd24c15364a5996bc6a675</Sha>
+      <Sha>8cafac4760a78176ef0e167bea66b97b65437930</Sha>
     </Dependency>
-    <Dependency Name="Microsoft.CodeAnalysis.Analyzers" Version="3.11.0-beta1.25173.3">
-      <Uri>https://github.com/dotnet/roslyn-analyzers</Uri>
-      <Sha>16865ea61910500f1022ad2b96c499e5df02c228</Sha>
+    <Dependency Name="Microsoft.CodeAnalysis.Analyzers" Version="3.12.0-beta1.25570.7">
+      <Uri>https://github.com/dotnet/roslyn</Uri>
+      <Sha>8cafac4760a78176ef0e167bea66b97b65437930</Sha>
     </Dependency>
     <Dependency Name="Microsoft.CodeAnalysis.NetAnalyzers" Version="9.0.0-preview.25173.3">
       <Uri>https://github.com/dotnet/roslyn-analyzers</Uri>
       <Sha>16865ea61910500f1022ad2b96c499e5df02c228</Sha>
     </Dependency>
     <!-- Intermediate is necessary for source build. -->
-    <Dependency Name="Microsoft.SourceBuild.Intermediate.roslyn" Version="4.12.0-3.25569.8">
+    <Dependency Name="Microsoft.SourceBuild.Intermediate.roslyn" Version="4.14.0-3.25570.7">
       <Uri>https://github.com/dotnet/roslyn</Uri>
-      <Sha>dc344ef24932dcd53cdd24c15364a5996bc6a675</Sha>
+      <Sha>8cafac4760a78176ef0e167bea66b97b65437930</Sha>
       <SourceBuild RepoName="roslyn" ManagedOnly="true" />
     </Dependency>
     <Dependency Name="Microsoft.DotNet.ApiCompat.Task" Version="9.0.109">
diff --git a/eng/Versions.props b/eng/Versions.props
index c17308ff4ff9cc..597f34b75879c7 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -36,7 +36,7 @@
   </ItemGroup>
   <PropertyGroup>
     <!-- dotnet/roslyn-analyzers dependencies -->
-    <MicrosoftCodeAnalysisAnalyzersVersion>3.11.0-beta1.25173.3</MicrosoftCodeAnalysisAnalyzersVersion>
+    <MicrosoftCodeAnalysisAnalyzersVersion>3.12.0-beta1.25570.7</MicrosoftCodeAnalysisAnalyzersVersion>
     <MicrosoftCodeAnalysisNetAnalyzersVersion>9.0.0-preview.25173.3</MicrosoftCodeAnalysisNetAnalyzersVersion>
     <!-- dotnet/roslyn dependencies -->
     <!--
@@ -44,9 +44,9 @@
       Any tools that contribute to the design-time experience should use the MicrosoftCodeAnalysisVersion_LatestVS property above to ensure
       they do not break the local dev experience.
     -->
-    <MicrosoftCodeAnalysisCSharpVersion>4.12.0-3.25569.8</MicrosoftCodeAnalysisCSharpVersion>
-    <MicrosoftCodeAnalysisVersion>4.12.0-3.25569.8</MicrosoftCodeAnalysisVersion>
-    <MicrosoftNetCompilersToolsetVersion>4.12.0-3.25569.8</MicrosoftNetCompilersToolsetVersion>
+    <MicrosoftCodeAnalysisCSharpVersion>4.14.0-3.25570.7</MicrosoftCodeAnalysisCSharpVersion>
+    <MicrosoftCodeAnalysisVersion>4.14.0-3.25570.7</MicrosoftCodeAnalysisVersion>
+    <MicrosoftNetCompilersToolsetVersion>4.14.0-3.25570.7</MicrosoftNetCompilersToolsetVersion>
   </PropertyGroup>
   <!--
     For source generator support we need to target multiple versions of Roslyn in order to be able to run on older versions of Roslyn.
diff --git a/src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/AssemblyChecker.cs b/src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/AssemblyChecker.cs
index bbe9184c4d7817..c62434f172dd2f 100644
--- a/src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/AssemblyChecker.cs
+++ b/src/coreclr/tools/aot/ILCompiler.Trimming.Tests/TestCasesRunner/AssemblyChecker.cs
@@ -977,7 +977,7 @@ private IEnumerable<string> VerifyReferences (AssemblyDefinition original, Assem
 				.Select (name => name.Name)
 				.ToArray ();
 
-			if (!actual.SequenceEqual(expected))
+			if (!actual!.SequenceEqual(expected))
 				yield return $"Expected references do not match actual references:\n\tExpected: {string.Join(", ", expected)}\n\tActual: {string.Join(", ", actual)}";
 		}
 
diff --git a/src/libraries/Common/tests/StreamConformanceTests/System/IO/StreamConformanceTests.cs b/src/libraries/Common/tests/StreamConformanceTests/System/IO/StreamConformanceTests.cs
index c36ce7c6feb0a0..119aa6667de378 100644
--- a/src/libraries/Common/tests/StreamConformanceTests/System/IO/StreamConformanceTests.cs
+++ b/src/libraries/Common/tests/StreamConformanceTests/System/IO/StreamConformanceTests.cs
@@ -1848,7 +1848,7 @@ public virtual async Task ReadWrite_MessagesSmallerThanReadBuffer_Success(ReadWr
                         }
 
                         Assert.Equal(writerBytes.Length, n);
-                        AssertExtensions.SequenceEqual(writerBytes, readerBytes.AsSpan(0, writerBytes.Length));
+                        AssertExtensions.SequenceEqual(writerBytes.AsSpan(), readerBytes.AsSpan(0, writerBytes.Length));
 
                         await writes;
                     }
@@ -2985,7 +2985,7 @@ public virtual async Task ZeroByteRead_PerformsZeroByteReadOnUnderlyingStreamWhe
 
                 if (FlushGuaranteesAllDataWritten)
                 {
-                    AssertExtensions.SequenceEqual(data, buffer.AsSpan(0, bytesRead));
+                    AssertExtensions.SequenceEqual(data.AsSpan(), buffer.AsSpan(0, bytesRead));
                 }
             }
         }
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/DependencyInjectionSpecificationTests.cs b/src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/DependencyInjectionSpecificationTests.cs
index dd910d35e102e8..46381662e03d02 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/DependencyInjectionSpecificationTests.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection.Specification.Tests/src/DependencyInjectionSpecificationTests.cs
@@ -900,7 +900,7 @@ public void DisposesInReverseOrderOfCreation()
 
             // Assert
             Assert.Equal(outer, callback.Disposed[0]);
-            Assert.Equal(multipleServices.Reverse(), callback.Disposed.Skip(1).Take(3).OfType<IFakeMultipleService>());
+            Assert.Equal(Enumerable.Reverse(multipleServices), callback.Disposed.Skip(1).Take(3).OfType<IFakeMultipleService>());
             Assert.Equal(outer.SingleService, callback.Disposed[4]);
         }
 
diff --git a/src/libraries/Microsoft.Extensions.Primitives/tests/StringValuesTests.cs b/src/libraries/Microsoft.Extensions.Primitives/tests/StringValuesTests.cs
index 5a0a0719ccc574..6cb9cb3c808491 100644
--- a/src/libraries/Microsoft.Extensions.Primitives/tests/StringValuesTests.cs
+++ b/src/libraries/Microsoft.Extensions.Primitives/tests/StringValuesTests.cs
@@ -453,19 +453,19 @@ public void DefaultNullOrEmpty_Concat(StringValues stringValues)
         {
             string[] expected = new[] { "abc", "bcd", "foo" };
             StringValues expectedStringValues = new StringValues(expected);
-            Assert.Equal(expected, StringValues.Concat(stringValues, expectedStringValues));
-            Assert.Equal(expected, StringValues.Concat(expectedStringValues, stringValues));
-            Assert.Equal(expected, StringValues.Concat((string)null, in expectedStringValues));
-            Assert.Equal(expected, StringValues.Concat(in expectedStringValues, (string)null));
+            Assert.Equal(expected, StringValues.Concat(stringValues, expectedStringValues).ToArray());
+            Assert.Equal(expected, StringValues.Concat(expectedStringValues, stringValues).ToArray());
+            Assert.Equal(expected, StringValues.Concat((string)null, in expectedStringValues).ToArray());
+            Assert.Equal(expected, StringValues.Concat(in expectedStringValues, (string)null).ToArray());
 
             string[] empty = new string[0];
             StringValues emptyStringValues = new StringValues(empty);
-            Assert.Equal(empty, StringValues.Concat(stringValues, StringValues.Empty));
-            Assert.Equal(empty, StringValues.Concat(StringValues.Empty, stringValues));
-            Assert.Equal(empty, StringValues.Concat(stringValues, new StringValues()));
-            Assert.Equal(empty, StringValues.Concat(new StringValues(), stringValues));
-            Assert.Equal(empty, StringValues.Concat((string)null, in emptyStringValues));
-            Assert.Equal(empty, StringValues.Concat(in emptyStringValues, (string)null));
+            Assert.Equal(empty, StringValues.Concat(stringValues, StringValues.Empty).ToArray());
+            Assert.Equal(empty, StringValues.Concat(StringValues.Empty, stringValues).ToArray());
+            Assert.Equal(empty, StringValues.Concat(stringValues, new StringValues()).ToArray());
+            Assert.Equal(empty, StringValues.Concat(new StringValues(), stringValues).ToArray());
+            Assert.Equal(empty, StringValues.Concat((string)null, in emptyStringValues).ToArray());
+            Assert.Equal(empty, StringValues.Concat(in emptyStringValues, (string)null).ToArray());
         }
 
         [Theory]
@@ -475,24 +475,24 @@ public void Concat(StringValues stringValues, string[] array)
             string[] filled = new[] { "abc", "bcd", "foo" };
 
             string[] expectedPrepended = array.Concat(filled).ToArray();
-            Assert.Equal(expectedPrepended, StringValues.Concat(stringValues, new StringValues(filled)));
+            Assert.Equal(expectedPrepended, StringValues.Concat(stringValues, new StringValues(filled)).ToArray());
 
             string[] expectedAppended = filled.Concat(array).ToArray();
-            Assert.Equal(expectedAppended, StringValues.Concat(new StringValues(filled), stringValues));
+            Assert.Equal(expectedAppended, StringValues.Concat(new StringValues(filled), stringValues).ToArray());
 
             StringValues values = stringValues;
             foreach (string s in filled)
             {
                 values = StringValues.Concat(in values, s);
             }
-            Assert.Equal(expectedPrepended, values);
+            Assert.Equal(expectedPrepended, (string[])values);
 
             values = stringValues;
-            foreach (string s in filled.Reverse())
+            foreach (string s in Enumerable.Reverse(filled))
             {
                 values = StringValues.Concat(s, in values);
             }
-            Assert.Equal(expectedAppended, values);
+            Assert.Equal(expectedAppended, (string[])values);
         }
 
         [Fact]
diff --git a/src/libraries/System.Collections.Immutable/tests/ImmutableStackTest.cs b/src/libraries/System.Collections.Immutable/tests/ImmutableStackTest.cs
index 4abd031ed43b2d..397990ee494971 100644
--- a/src/libraries/System.Collections.Immutable/tests/ImmutableStackTest.cs
+++ b/src/libraries/System.Collections.Immutable/tests/ImmutableStackTest.cs
@@ -305,7 +305,7 @@ public void PeekRef_Empty()
         protected override IEnumerable<T> GetEnumerableOf<T>(params T[] contents)
         {
             ImmutableStack<T> stack = ImmutableStack<T>.Empty;
-            foreach (T value in contents.Reverse())
+            foreach (T value in Enumerable.Reverse(contents))
             {
                 stack = stack.Push(value);
             }
diff --git a/src/libraries/System.Collections.Specialized/tests/ListDictionaryTests.cs b/src/libraries/System.Collections.Specialized/tests/ListDictionaryTests.cs
index e1e2d9da040da8..abbecf3bd18c1c 100644
--- a/src/libraries/System.Collections.Specialized/tests/ListDictionaryTests.cs
+++ b/src/libraries/System.Collections.Specialized/tests/ListDictionaryTests.cs
@@ -137,7 +137,7 @@ public static void Set_CustomComparerTest()
 
             int visited = s_dictionaryData.Length;
 
-            Assert.All(s_dictionaryData.Reverse(), element =>
+            Assert.All(Enumerable.Reverse(s_dictionaryData), element =>
             {
                 string newValue = "new" + element.Value;
                 Assert.True(ld.Contains(element.Key));
@@ -154,7 +154,7 @@ public static void Remove_CustomComparerTest()
             ObservableStringComparer comparer = new ObservableStringComparer();
             ListDictionary ld = Fill(new ListDictionary(comparer), s_dictionaryData);
 
-            Assert.All(s_dictionaryData.Reverse(), element =>
+            Assert.All(Enumerable.Reverse(s_dictionaryData), element =>
             {
                 int originalSize = ld.Count;
                 Assert.True(ld.Contains(element.Key));
diff --git a/src/libraries/System.Collections/tests/Generic/Queue/Queue.Generic.Tests.cs b/src/libraries/System.Collections/tests/Generic/Queue/Queue.Generic.Tests.cs
index 7c900d4c6ef325..e5adef0e878d7a 100644
--- a/src/libraries/System.Collections/tests/Generic/Queue/Queue.Generic.Tests.cs
+++ b/src/libraries/System.Collections/tests/Generic/Queue/Queue.Generic.Tests.cs
@@ -181,7 +181,6 @@ public void Queue_Generic_ToArray_NonWrappedQueue(int count)
             Queue<T> collection = new Queue<T>(count + 1);
             AddToCollection(collection, count);
             T[] elements = collection.ToArray();
-            elements.Reverse();
             Assert.True(Enumerable.SequenceEqual(elements, collection.ToArray<T>()));
         }
 
diff --git a/src/libraries/System.Collections/tests/Generic/Stack/Stack.Generic.Tests.cs b/src/libraries/System.Collections/tests/Generic/Stack/Stack.Generic.Tests.cs
index a3e04713f1d6aa..8c032eff8f7deb 100644
--- a/src/libraries/System.Collections/tests/Generic/Stack/Stack.Generic.Tests.cs
+++ b/src/libraries/System.Collections/tests/Generic/Stack/Stack.Generic.Tests.cs
@@ -80,7 +80,7 @@ public void Stack_Generic_Constructor_IEnumerable(EnumerableType enumerableType,
             _ = numberOfMatchingElements;
             IEnumerable<T> enumerable = CreateEnumerable(enumerableType, null, enumerableLength, 0, numberOfDuplicateElements);
             Stack<T> stack = new Stack<T>(enumerable);
-            Assert.Equal(enumerable.ToArray().Reverse(), stack.ToArray());
+            Assert.Equal(Enumerable.Reverse(enumerable.ToArray()), stack.ToArray());
         }
 
         [Fact]
diff --git a/src/libraries/System.ComponentModel.Composition/tests/System/ComponentModel/Composition/CompositionErrorTests.cs b/src/libraries/System.ComponentModel.Composition/tests/System/ComponentModel/Composition/CompositionErrorTests.cs
index 4dbd14618a3165..0a0b4e7ed09a60 100644
--- a/src/libraries/System.ComponentModel.Composition/tests/System/ComponentModel/Composition/CompositionErrorTests.cs
+++ b/src/libraries/System.ComponentModel.Composition/tests/System/ComponentModel/Composition/CompositionErrorTests.cs
@@ -416,7 +416,7 @@ private static CompositionError CreateCompositionError(CompositionErrorId id, st
         private static CompositionError CreateCompositionError(params string[] messages)
         {
             CompositionError error = null;
-            foreach (string message in messages.Reverse())
+            foreach (string message in Enumerable.Reverse(messages))
             {
                 CompositionException exception = null;
                 if (error != null)
diff --git a/src/libraries/System.Diagnostics.TraceSource/tests/System.Diagnostics.TraceSource.Tests/TraceListenerClassTests.cs b/src/libraries/System.Diagnostics.TraceSource/tests/System.Diagnostics.TraceSource.Tests/TraceListenerClassTests.cs
index a2e60be4859335..095bfac1763b70 100644
--- a/src/libraries/System.Diagnostics.TraceSource/tests/System.Diagnostics.TraceSource.Tests/TraceListenerClassTests.cs
+++ b/src/libraries/System.Diagnostics.TraceSource/tests/System.Diagnostics.TraceSource.Tests/TraceListenerClassTests.cs
@@ -358,7 +358,7 @@ public void WriteFooterTest_LogicalOperationStack()
                     listener.Flush();
 
                     Assert.Contains("LogicalOperationStack=", listener.Output);
-                    Assert.Contains(string.Join(", ", items.Reverse()), listener.Output);
+                    Assert.Contains(string.Join(", ", Enumerable.Reverse(items)), listener.Output);
                 }
                 finally
                 {
diff --git a/src/libraries/System.Formats.Nrbf/src/System/Formats/Nrbf/ArraySinglePrimitiveRecord.cs b/src/libraries/System.Formats.Nrbf/src/System/Formats/Nrbf/ArraySinglePrimitiveRecord.cs
index a28359d9bb13dc..ef2195a342a04d 100644
--- a/src/libraries/System.Formats.Nrbf/src/System/Formats/Nrbf/ArraySinglePrimitiveRecord.cs
+++ b/src/libraries/System.Formats.Nrbf/src/System/Formats/Nrbf/ArraySinglePrimitiveRecord.cs
@@ -161,7 +161,7 @@ internal static IReadOnlyList<T> DecodePrimitiveTypes(BinaryReader reader, int c
         {
             if (typeof(T) == typeof(short) || typeof(T) == typeof(ushort))
             {
-                Span<short> span = MemoryMarshal.Cast<T, short>(result);
+                Span<short> span = MemoryMarshal.Cast<T, short>(result.AsSpan());
 #if NET
                 BinaryPrimitives.ReverseEndianness(span, span);
 #else
@@ -173,7 +173,7 @@ internal static IReadOnlyList<T> DecodePrimitiveTypes(BinaryReader reader, int c
             }
             else if (typeof(T) == typeof(int) || typeof(T) == typeof(uint) || typeof(T) == typeof(float))
             {
-                Span<int> span = MemoryMarshal.Cast<T, int>(result);
+                Span<int> span = MemoryMarshal.Cast<T, int>(result.AsSpan());
 #if NET
                 BinaryPrimitives.ReverseEndianness(span, span);
 #else
@@ -185,7 +185,7 @@ internal static IReadOnlyList<T> DecodePrimitiveTypes(BinaryReader reader, int c
             }
             else if (typeof(T) == typeof(long) || typeof(T) == typeof(ulong) || typeof(T) == typeof(double))
             {
-                Span<long> span = MemoryMarshal.Cast<T, long>(result);
+                Span<long> span = MemoryMarshal.Cast<T, long>(result.AsSpan());
 #if NET
                 BinaryPrimitives.ReverseEndianness(span, span);
 #else
@@ -201,7 +201,7 @@ internal static IReadOnlyList<T> DecodePrimitiveTypes(BinaryReader reader, int c
         {
             // See DontCastBytesToBooleans test to see what could go wrong.
             bool[] booleans = (bool[])(object)result;
-            Span<byte> resultAsBytes = MemoryMarshal.AsBytes<T>(result);
+            Span<byte> resultAsBytes = MemoryMarshal.AsBytes<T>(result.AsSpan());
             for (int i = 0; i < booleans.Length; i++)
             {
                 // We don't use the bool array to get the value, as an optimizing compiler or JIT could elide this.
diff --git a/src/libraries/System.Linq/tests/RangeTests.cs b/src/libraries/System.Linq/tests/RangeTests.cs
index 2e331cfee7ecd7..26ec544f327af7 100644
--- a/src/libraries/System.Linq/tests/RangeTests.cs
+++ b/src/libraries/System.Linq/tests/RangeTests.cs
@@ -270,7 +270,7 @@ static void Validate(IEnumerable<int> e, int[] expected)
                 list.CopyTo(actual, 1);
                 Assert.Equal(0, actual[0]);
                 Assert.Equal(0, actual[^1]);
-                AssertExtensions.SequenceEqual(expected, actual.AsSpan(1, expected.Length));
+                AssertExtensions.SequenceEqual(expected.AsSpan(), actual.AsSpan(1, expected.Length));
             }
         }
     }
diff --git a/src/libraries/System.Linq/tests/RepeatTests.cs b/src/libraries/System.Linq/tests/RepeatTests.cs
index df8eebda35691e..9ee0d7f68fb146 100644
--- a/src/libraries/System.Linq/tests/RepeatTests.cs
+++ b/src/libraries/System.Linq/tests/RepeatTests.cs
@@ -282,7 +282,7 @@ static void Validate(IEnumerable<int> e, int[] expected)
                 list.CopyTo(actual, 1);
                 Assert.Equal(0, actual[0]);
                 Assert.Equal(0, actual[^1]);
-                AssertExtensions.SequenceEqual(expected, actual.AsSpan(1, expected.Length));
+                AssertExtensions.SequenceEqual(expected.AsSpan(), actual.AsSpan(1, expected.Length));
             }
         }
     }
diff --git a/src/libraries/System.Memory/tests/Base64Url/Base64UrlUnicodeAPIsUnitTests.cs b/src/libraries/System.Memory/tests/Base64Url/Base64UrlUnicodeAPIsUnitTests.cs
index 0d39bc7854bc24..350a6c3112c11b 100644
--- a/src/libraries/System.Memory/tests/Base64Url/Base64UrlUnicodeAPIsUnitTests.cs
+++ b/src/libraries/System.Memory/tests/Base64Url/Base64UrlUnicodeAPIsUnitTests.cs
@@ -438,7 +438,7 @@ public static void Base64_AllMethodsRoundtripConsistently()
                 Span<byte> decodedBytes = new byte[original.Length];
                 int decoded = Base64Url.DecodeFromChars(encodedArray, decodedBytes);
                 Assert.Equal(original.Length, decoded);
-                AssertExtensions.SequenceEqual(original, decodedBytes);
+                AssertExtensions.SequenceEqual(original.AsSpan(), decodedBytes);
 
                 byte[] actualBytes = new byte[original.Length];
                 Assert.True(Base64Url.TryDecodeFromChars(encodedSpan, actualBytes, out int bytesWritten));
diff --git a/src/libraries/System.Memory/tests/Memory/CopyTo.cs b/src/libraries/System.Memory/tests/Memory/CopyTo.cs
index 69f9f1fd2a4423..c88fd64d52e5d4 100644
--- a/src/libraries/System.Memory/tests/Memory/CopyTo.cs
+++ b/src/libraries/System.Memory/tests/Memory/CopyTo.cs
@@ -41,7 +41,7 @@ public static void TryCopyToArraySegmentImplicit()
             Memory<int> srcMemory = src;
             bool success = srcMemory.TryCopyTo(segment);
             Assert.True(success);
-            Assert.Equal(src, segment);
+            Assert.Equal(src.AsSpan(), segment);
         }
 
         [Fact]
diff --git a/src/libraries/System.Memory/tests/MemoryMarshal/GetArrayDataReference.cs b/src/libraries/System.Memory/tests/MemoryMarshal/GetArrayDataReference.cs
index c3478421c358c1..d76867c5c76820 100644
--- a/src/libraries/System.Memory/tests/MemoryMarshal/GetArrayDataReference.cs
+++ b/src/libraries/System.Memory/tests/MemoryMarshal/GetArrayDataReference.cs
@@ -90,7 +90,9 @@ public static void GetArrayDataReference_IgnoresArrayVarianceChecks()
 
         private sealed class RawObject
         {
+            #pragma warning disable CS0649 // Field is never assigned to, and will always have its default value null
             internal byte Data;
+            #pragma warning restore CS0649
         }
     }
 }
diff --git a/src/libraries/System.Memory/tests/ReadOnlySpan/CopyTo.cs b/src/libraries/System.Memory/tests/ReadOnlySpan/CopyTo.cs
index 578f7867ac96ce..0d297485f7a40f 100644
--- a/src/libraries/System.Memory/tests/ReadOnlySpan/CopyTo.cs
+++ b/src/libraries/System.Memory/tests/ReadOnlySpan/CopyTo.cs
@@ -42,7 +42,7 @@ public static void TryCopyToArraySegmentImplicit()
             ReadOnlySpan<int> srcSpan = new ReadOnlySpan<int>(src);
             bool success = srcSpan.TryCopyTo(segment);
             Assert.True(success);
-            Assert.Equal(src, segment);
+            Assert.Equal(src.AsSpan(), segment);
         }
 
         [Fact]
diff --git a/src/libraries/System.Memory/tests/Span/CopyTo.cs b/src/libraries/System.Memory/tests/Span/CopyTo.cs
index 0e87eea54c61fc..4b10f5d00bdb1e 100644
--- a/src/libraries/System.Memory/tests/Span/CopyTo.cs
+++ b/src/libraries/System.Memory/tests/Span/CopyTo.cs
@@ -42,7 +42,7 @@ public static void TryCopyToArraySegmentImplicit()
             Span<int> srcSpan = new Span<int>(src);
             bool success = srcSpan.TryCopyTo(segment);
             Assert.True(success);
-            Assert.Equal(src, segment);
+            Assert.Equal(src.AsSpan(), segment);
         }
 
         [Fact]
diff --git a/src/libraries/System.Memory/tests/Span/SearchValues.cs b/src/libraries/System.Memory/tests/Span/SearchValues.cs
index 8f39a95bd3c0f4..361830f38364c0 100644
--- a/src/libraries/System.Memory/tests/Span/SearchValues.cs
+++ b/src/libraries/System.Memory/tests/Span/SearchValues.cs
@@ -458,7 +458,7 @@ static SearchValuesTestHelper()
                     s_randomLatin1Chars[i] = (char)rng.Next(0, 256);
                 }
 
-                rng.NextBytes(MemoryMarshal.Cast<char, byte>(s_randomChars));
+                rng.NextBytes(MemoryMarshal.Cast<char, byte>(s_randomChars.AsSpan()));
 
                 s_randomAsciiBytes = Encoding.ASCII.GetBytes(s_randomAsciiChars);
 
diff --git a/src/libraries/System.Memory/tests/Span/StringSearchValues.cs b/src/libraries/System.Memory/tests/Span/StringSearchValues.cs
index c0b80b5ab06776..f702b0bdcad99d 100644
--- a/src/libraries/System.Memory/tests/Span/StringSearchValues.cs
+++ b/src/libraries/System.Memory/tests/Span/StringSearchValues.cs
@@ -620,7 +620,7 @@ public StringSearchValuesTestHelper(IndexOfAnySearchDelegate expected, SearchVal
                     }));
                 }
 
-                rng.NextBytes(MemoryMarshal.Cast<char, byte>(_randomChars));
+                rng.NextBytes(MemoryMarshal.Cast<char, byte>(_randomChars.AsSpan()));
             }
 
             public void StressRandomInputs(TimeSpan duration)
diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpHeaders.cs b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpHeaders.cs
index 03b5934ea38dc1..ef8b5f06288463 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpHeaders.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/Headers/HttpHeaders.cs
@@ -1165,7 +1165,7 @@ internal static void GetStoreValuesAsStringOrStringArray(HeaderDescriptor descri
                 else
                 {
                     Debug.Assert(length > 1, "The header should have been removed when it became empty");
-                    values = multiValue = new string[length];
+                    values = (multiValue = new string[length])!;
                 }
 
                 int currentIndex = 0;
@@ -1205,8 +1205,8 @@ internal static int GetStoreValuesIntoStringArray(HeaderDescriptor descriptor, o
                 }
 
                 int currentIndex = 0;
-                ReadStoreValues<object?>(values, info.ParsedAndInvalidValues, descriptor.Parser, ref currentIndex);
-                ReadStoreValues<string?>(values, info.RawValue, null, ref currentIndex);
+                ReadStoreValues<object?>(values!, info.ParsedAndInvalidValues, descriptor.Parser, ref currentIndex);
+                ReadStoreValues<string?>(values!, info.RawValue, null, ref currentIndex);
                 Debug.Assert(currentIndex == length);
 
                 return length;
diff --git a/src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketAsyncEventArgsTest.cs b/src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketAsyncEventArgsTest.cs
index afd56dfcc9ef76..8f5cd1c6f0dac2 100644
--- a/src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketAsyncEventArgsTest.cs
+++ b/src/libraries/System.Net.Sockets/tests/FunctionalTests/SocketAsyncEventArgsTest.cs
@@ -727,7 +727,7 @@ public void AcceptAsync_WithReceiveBuffer_Success()
 
                 Assert.Equal(acceptBufferDataSize, acceptArgs.BytesTransferred);
 
-                AssertExtensions.SequenceEqual(sendBuffer, acceptArgs.Buffer.AsSpan(0, acceptArgs.BytesTransferred));
+                AssertExtensions.SequenceEqual(sendBuffer.AsSpan(), acceptArgs.Buffer.AsSpan(0, acceptArgs.BytesTransferred));
             }
         }
 
diff --git a/src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorExtensions.cs b/src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorExtensions.cs
index 8c8f02970db525..414e3c55d91f21 100644
--- a/src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorExtensions.cs
+++ b/src/libraries/System.Numerics.Tensors/src/System/Numerics/Tensors/netcore/TensorExtensions.cs
@@ -2658,7 +2658,7 @@ public static Tensor<T> PermuteDimensions<T>(this Tensor<T> tensor, params ReadO
 
                 if (dimensions.IsEmpty)
                 {
-                    lengths = tensor._lengths.Reverse().ToArray();
+                    lengths = Enumerable.Reverse(tensor._lengths).ToArray();
                     permutation = Enumerable.Range(0, tensor.Rank).Reverse().ToArray();
                 }
                 else
diff --git a/src/libraries/System.Numerics.Tensors/tests/TensorTests.cs b/src/libraries/System.Numerics.Tensors/tests/TensorTests.cs
index b1ad7a4c2d78cf..357fb4c295f90f 100644
--- a/src/libraries/System.Numerics.Tensors/tests/TensorTests.cs
+++ b/src/libraries/System.Numerics.Tensors/tests/TensorTests.cs
@@ -684,7 +684,7 @@ public static void TensorMultiplyTests()
             Tensor<int> t1 = Tensor.Create(Enumerable.Range(0, 3), [3, 1]);
             Tensor<int> t2 = Tensor.Multiply(t0.AsReadOnlyTensorSpan(), t1);
 
-            Assert.Equal([3,3], t2.Lengths.ToArray());
+            Assert.Equal([3,3], t2.Lengths);
             Assert.Equal(0, t2[0, 0]);
             Assert.Equal(0, t2[0, 1]);
             Assert.Equal(0, t2[0, 2]);
@@ -697,7 +697,7 @@ public static void TensorMultiplyTests()
 
             t2 = Tensor.Multiply(t1.AsReadOnlyTensorSpan(), t0);
 
-            Assert.Equal([3, 3], t2.Lengths.ToArray());
+            Assert.Equal([3, 3], t2.Lengths);
             Assert.Equal(0, t2[0, 0]);
             Assert.Equal(0, t2[0, 1]);
             Assert.Equal(0, t2[0, 2]);
@@ -711,7 +711,7 @@ public static void TensorMultiplyTests()
             t1 = Tensor.Create(Enumerable.Range(0, 9), [3, 3]);
             t2 = Tensor.Multiply(t0.AsReadOnlyTensorSpan(), t1);
 
-            Assert.Equal([3, 3], t2.Lengths.ToArray());
+            Assert.Equal([3, 3], t2.Lengths);
             Assert.Equal(0, t2[0, 0]);
             Assert.Equal(1, t2[0, 1]);
             Assert.Equal(4, t2[0, 2]);
@@ -729,7 +729,7 @@ public static void TensorBroadcastTests()
             Tensor<int> t0 = Tensor.Create(Enumerable.Range(0, 3), [1, 3, 1, 1, 1]);
             Tensor<int> t1 = Tensor.Broadcast<int>(t0, [1, 3, 1, 2, 1]);
 
-            Assert.Equal([1, 3, 1, 2, 1], t1.Lengths.ToArray());
+            Assert.Equal([1, 3, 1, 2, 1], t1.Lengths);
 
             Assert.Equal(0, t1[0, 0, 0, 0, 0]);
             Assert.Equal(0, t1[0, 0, 0, 1, 0]);
@@ -739,7 +739,7 @@ public static void TensorBroadcastTests()
             Assert.Equal(2, t1[0, 2, 0, 1, 0]);
 
             t1 = Tensor.Broadcast<int>(t0, [1, 3, 2, 1, 1]);
-            Assert.Equal([1, 3, 2, 1, 1], t1.Lengths.ToArray());
+            Assert.Equal([1, 3, 2, 1, 1], t1.Lengths);
 
             Assert.Equal(0, t1[0, 0, 0, 0, 0]);
             Assert.Equal(0, t1[0, 0, 1, 0, 0]);
@@ -751,7 +751,7 @@ public static void TensorBroadcastTests()
             t0 = Tensor.Create(Enumerable.Range(0, 3), [1, 3]);
             t1 = Tensor.Create(Enumerable.Range(0, 3), [3, 1]);
             var t2 = Tensor.Broadcast<int>(t0, [3, 3]);
-            Assert.Equal([3, 3], t2.Lengths.ToArray());
+            Assert.Equal([3, 3], t2.Lengths);
 
             Assert.Equal(0, t2[0, 0]);
             Assert.Equal(1, t2[0, 1]);
@@ -765,7 +765,7 @@ public static void TensorBroadcastTests()
 
             t1 = Tensor.Create(Enumerable.Range(0, 3), [3, 1]);
             t2 = Tensor.Broadcast<int>(t1, [3, 3]);
-            Assert.Equal([3, 3], t2.Lengths.ToArray());
+            Assert.Equal([3, 3], t2.Lengths);
 
             Assert.Equal(0, t2[0, 0]);
             Assert.Equal(0, t2[0, 1]);
@@ -789,11 +789,11 @@ public static void TensorBroadcastTests()
             Assert.Equal(2, s1[2, 2]);
 
             var t3 = t2.Slice(0..1, ..);
-            Assert.Equal([1, 3], t3.Lengths.ToArray());
+            Assert.Equal([1, 3], t3.Lengths);
 
             t1 = Tensor.Create(Enumerable.Range(0, 3), default);
             t2 = Tensor.Broadcast<int>(t1, [3, 3]);
-            Assert.Equal([3, 3], t2.Lengths.ToArray());
+            Assert.Equal([3, 3], t2.Lengths);
 
             Assert.Equal(0, t2[0, 0]);
             Assert.Equal(1, t2[0, 1]);
@@ -811,15 +811,15 @@ public static void TensorResizeTests()
         {
             Tensor<int> t0 = Tensor.Create(Enumerable.Range(0, 8), [2, 2, 2]);
             var t1 = Tensor.Resize(t0, [1]);
-            Assert.Equal([1], t1.Lengths.ToArray());
+            Assert.Equal([1], t1.Lengths);
             Assert.Equal(0, t1[0]);
 
             t1 = Tensor.Resize(t0, [1, 1]);
-            Assert.Equal([1, 1], t1.Lengths.ToArray());
+            Assert.Equal([1, 1], t1.Lengths);
             Assert.Equal(0, t1[0, 0]);
 
             t1 = Tensor.Resize(t0, [6]);
-            Assert.Equal([6], t1.Lengths.ToArray());
+            Assert.Equal([6], t1.Lengths);
             Assert.Equal(0, t1[0]);
             Assert.Equal(1, t1[1]);
             Assert.Equal(2, t1[2]);
@@ -828,7 +828,7 @@ public static void TensorResizeTests()
             Assert.Equal(5, t1[5]);
 
             t1 = Tensor.Resize(t0, [10]);
-            Assert.Equal([10], t1.Lengths.ToArray());
+            Assert.Equal([10], t1.Lengths);
             Assert.Equal(0, t1[0]);
             Assert.Equal(1, t1[1]);
             Assert.Equal(2, t1[2]);
@@ -841,7 +841,7 @@ public static void TensorResizeTests()
             Assert.Equal(0, t1[9]);
 
             t1 = Tensor.Resize(t0, [2, 5]);
-            Assert.Equal([2, 5], t1.Lengths.ToArray());
+            Assert.Equal([2, 5], t1.Lengths);
             Assert.Equal(0, t1[0, 0]);
             Assert.Equal(1, t1[0, 1]);
             Assert.Equal(2, t1[0, 2]);
@@ -859,8 +859,8 @@ public static void TensorSplitTests()
         {
             Tensor<int> t0 = Tensor.Create(Enumerable.Range(0, 8), [2, 2, 2]);
             var t1 = Tensor.Split<int>(t0, 2, 0);
-            Assert.Equal([1, 2, 2], t1[0].Lengths.ToArray());
-            Assert.Equal([1, 2, 2], t1[1].Lengths.ToArray());
+            Assert.Equal([1, 2, 2], t1[0].Lengths);
+            Assert.Equal([1, 2, 2], t1[1].Lengths);
             Assert.Equal(0, t1[0][0, 0, 0]);
             Assert.Equal(1, t1[0][0, 0, 1]);
             Assert.Equal(2, t1[0][0, 1, 0]);
@@ -871,8 +871,8 @@ public static void TensorSplitTests()
             Assert.Equal(7, t1[1][0, 1, 1]);
 
             t1 = Tensor.Split<int>(t0, 2, 1);
-            Assert.Equal([2, 1, 2], t1[0].Lengths.ToArray());
-            Assert.Equal([2, 1, 2], t1[1].Lengths.ToArray());
+            Assert.Equal([2, 1, 2], t1[0].Lengths);
+            Assert.Equal([2, 1, 2], t1[1].Lengths);
             Assert.Equal(0, t1[0][0, 0, 0]);
             Assert.Equal(1, t1[0][0, 0, 1]);
             Assert.Equal(4, t1[0][1, 0, 0]);
@@ -883,8 +883,8 @@ public static void TensorSplitTests()
             Assert.Equal(7, t1[1][1, 0, 1]);
 
             t1 = Tensor.Split<int>(t0, 2, 2);
-            Assert.Equal([2, 2, 1], t1[0].Lengths.ToArray());
-            Assert.Equal([2, 2, 1], t1[1].Lengths.ToArray());
+            Assert.Equal([2, 2, 1], t1[0].Lengths);
+            Assert.Equal([2, 2, 1], t1[1].Lengths);
             Assert.Equal(0, t1[0][0, 0, 0]);
             Assert.Equal(2, t1[0][0, 1, 0]);
             Assert.Equal(4, t1[0][1, 0, 0]);
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatefulLinearCollectionShapeValidation.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatefulLinearCollectionShapeValidation.cs
index 2aedfde9936f47..e798e184b6bf76 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatefulLinearCollectionShapeValidation.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatefulLinearCollectionShapeValidation.cs
@@ -171,7 +171,7 @@ public void FromManaged(ManagedType m) {}
                     public nint ToUnmanaged() => default;
                     public void Free() {}
                     public Span<T> GetUnmanagedValuesDestination() => default;
-                
+
                     public ReadOnlySpan<nint> GetManagedValuesSource()
                     {
                         throw new NotImplementedException();
@@ -602,7 +602,6 @@ public void FromManaged(ManagedType m, Span<byte> buffer) {}
                     public void Free() {}
                     public ReadOnlySpan<byte> GetManagedValuesSource() => default;
                     public Span<T> GetUnmanagedValuesDestination() => default;
-
                     public static int BufferSize
                     {
                         get
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatefulValueShapeValidation.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatefulValueShapeValidation.cs
index 9a72a5fbc4916f..cb2c5d8caf10ec 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatefulValueShapeValidation.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatefulValueShapeValidation.cs
@@ -382,7 +382,6 @@ public void FromManaged(ManagedType m, Span<byte> b) {}
                     public int ToUnmanaged() => default;
 
                     public void Free() {}
-
                     public static int BufferSize
                     {
                         get
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatelessLinearCollectionShapeValidation.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatelessLinearCollectionShapeValidation.cs
index fec16b2bc7ff7c..b60bb78f2acc2b 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatelessLinearCollectionShapeValidation.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatelessLinearCollectionShapeValidation.cs
@@ -614,7 +614,6 @@ static class MarshallerType<T>
                     public static ReadOnlySpan<int> GetManagedValuesSource(ManagedType m) => default;
 
                     public static Span<T> GetUnmanagedValuesDestination(nint unmanaged, int numElements) => default;
-
                     public static int BufferSize
                     {
                         get
diff --git a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatelessValueShapeValidation.cs b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatelessValueShapeValidation.cs
index 7d94afb9985f79..35c90af32f81b2 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatelessValueShapeValidation.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/LibraryImportGenerator.UnitTests/CustomMarshallerAttributeFixerTests_StatelessValueShapeValidation.cs
@@ -363,7 +363,6 @@ class ManagedType {}
                 static class MarshallerType
                 {
                     public static nint ConvertToUnmanaged(ManagedType m, Span<byte> b) => default;
-
                     public static int BufferSize
                     {
                         get
diff --git a/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/CollectionsMarshalTests.cs b/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/CollectionsMarshalTests.cs
index 325c9a43de6303..867ee99b852e89 100644
--- a/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/CollectionsMarshalTests.cs
+++ b/src/libraries/System.Runtime.InteropServices/tests/System.Runtime.InteropServices.UnitTests/System/Runtime/InteropServices/CollectionsMarshalTests.cs
@@ -527,19 +527,19 @@ public void ListSetCount()
             CollectionsMarshal.SetCount(list, 3);
             Assert.Equal(3, list.Count);
             Assert.Throws<ArgumentOutOfRangeException>(() => list[3]);
-            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(list), new int[] { 1, 2, 3 });
+            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(list), new int[] { 1, 2, 3 }.AsSpan());
             Assert.True(Unsafe.AreSame(ref intRef, ref MemoryMarshal.GetReference(CollectionsMarshal.AsSpan(list))));
 
             // make sure that size increase preserves content and doesn't clear
             CollectionsMarshal.SetCount(list, 5);
-            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(list), new int[] { 1, 2, 3, 4, 5 });
+            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(list), new int[] { 1, 2, 3, 4, 5 }.AsSpan());
             Assert.True(Unsafe.AreSame(ref intRef, ref MemoryMarshal.GetReference(CollectionsMarshal.AsSpan(list))));
 
             // make sure that reallocations preserve content
             int newCount = list.Capacity * 2;
             CollectionsMarshal.SetCount(list, newCount);
             Assert.Equal(newCount, list.Count);
-            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(list)[..3], new int[] { 1, 2, 3 });
+            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(list)[..3], new int[] { 1, 2, 3 }.AsSpan());
             Assert.True(!Unsafe.AreSame(ref intRef, ref MemoryMarshal.GetReference(CollectionsMarshal.AsSpan(list))));
 
             List<string> listReference = new() { "a", "b", "c", "d", "e" };
@@ -547,12 +547,12 @@ public void ListSetCount()
             CollectionsMarshal.SetCount(listReference, 3);
 
             // verify that reference types aren't cleared
-            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(listReference), new string[] { "a", "b", "c" });
+            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(listReference), new string[] { "a", "b", "c" }.AsSpan());
             Assert.True(Unsafe.AreSame(ref stringRef, ref MemoryMarshal.GetReference(CollectionsMarshal.AsSpan(listReference))));
             CollectionsMarshal.SetCount(listReference, 5);
 
             // verify that removed reference types are cleared
-            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(listReference), new string[] { "a", "b", "c", null, null });
+            AssertExtensions.SequenceEqual(CollectionsMarshal.AsSpan(listReference), new string[] { "a", "b", "c", null, null }.AsSpan());
             Assert.True(Unsafe.AreSame(ref stringRef, ref MemoryMarshal.GetReference(CollectionsMarshal.AsSpan(listReference))));
         }
     }
diff --git a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs
index e173705da39c47..6a9a0e52afa7fd 100644
--- a/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs
+++ b/src/libraries/System.Runtime.Numerics/src/System/Numerics/BigInteger.cs
@@ -384,7 +384,7 @@ public BigInteger(ReadOnlySpan<byte> value, bool isUnsigned = false, bool isBigE
                     // The bytes parameter is in little-endian byte order.
                     // We can just copy the bytes directly into the uint array.
 
-                    value.Slice(0, wholeUInt32Count * 4).CopyTo(MemoryMarshal.AsBytes<uint>(val));
+                    value.Slice(0, wholeUInt32Count * 4).CopyTo(MemoryMarshal.AsBytes<uint>(val.AsSpan()));
                 }
 
                 // In both of the above cases on big-endian architecture, we need to perform
diff --git a/src/libraries/System.Runtime/tests/System.Diagnostics.Debug.Tests/System.Diagnostics.Debug.Tests.csproj b/src/libraries/System.Runtime/tests/System.Diagnostics.Debug.Tests/System.Diagnostics.Debug.Tests.csproj
index f27284e29a9079..8cd911f50213dc 100644
--- a/src/libraries/System.Runtime/tests/System.Diagnostics.Debug.Tests/System.Diagnostics.Debug.Tests.csproj
+++ b/src/libraries/System.Runtime/tests/System.Diagnostics.Debug.Tests/System.Diagnostics.Debug.Tests.csproj
@@ -13,6 +13,7 @@
     <ProjectReference Include="$(CoreLibProject)" />
     <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\src\System.Runtime.csproj" />
     <ProjectReference Include="$(LibrariesProjectRoot)System.Collections\src\System.Collections.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Memory\src\System.Memory.csproj" />
     <ProjectReference Include="$(LibrariesProjectRoot)System.Threading\src\System.Threading.csproj" />
   </ItemGroup>
   <ItemGroup>
diff --git a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/GraphemeBreakTest.cs b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/GraphemeBreakTest.cs
index c741edd8829661..e7edba854fae70 100644
--- a/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/GraphemeBreakTest.cs
+++ b/src/libraries/System.Runtime/tests/System.Globalization.Tests/System/Globalization/GraphemeBreakTest.cs
@@ -141,7 +141,7 @@ public void VisualBasicReverseString()
                 // Arrange
 
                 string forwardActual = string.Concat(clusters.SelectMany(cluster => cluster).Select(rune => rune.ToString()));
-                string reverseExpected = string.Concat(clusters.Reverse().SelectMany(cluster => cluster).Select(rune => rune.ToString()));
+                string reverseExpected = string.Concat(Enumerable.Reverse(clusters).SelectMany(cluster => cluster).Select(rune => rune.ToString()));
 
                 // Act
 
diff --git a/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/FileStream/ReadAsync.cs b/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/FileStream/ReadAsync.cs
index d31149d297c5e0..40220b45ef875a 100644
--- a/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/FileStream/ReadAsync.cs
+++ b/src/libraries/System.Runtime/tests/System.IO.FileSystem.Tests/FileStream/ReadAsync.cs
@@ -123,7 +123,7 @@ public async Task IncompleteReadCantSetPositionBeyondEndOfFile(FileShare fileSha
                 await Task.WhenAll(reads);
                 // but when they are finished, the first buffer should contain valid data:
                 Assert.Equal(fileSize, reads.First().Result);
-                AssertExtensions.SequenceEqual(content, buffers.First().AsSpan(0, fileSize));
+                AssertExtensions.SequenceEqual(content.AsSpan(), buffers.First().AsSpan(0, fileSize));
                 // and other reads should return 0:
                 Assert.All(reads.Skip(1), read => Assert.Equal(0, read.Result));
                 // and the Position must be correct:
diff --git a/src/libraries/System.Runtime/tests/System.Reflection.Tests/FieldInfoTests.cs b/src/libraries/System.Runtime/tests/System.Reflection.Tests/FieldInfoTests.cs
index c3ff97fb342297..d8c6425f3b1a72 100644
--- a/src/libraries/System.Runtime/tests/System.Reflection.Tests/FieldInfoTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Reflection.Tests/FieldInfoTests.cs
@@ -868,7 +868,9 @@ public static class SettingsForMyTypeThatThrowsInClassInitializer
 
         private class RawData
         {
+            #pragma warning disable CS0649 // Field is never assigned to, and will always have its default value null
             public byte Data;
+            #pragma warning restore CS0649
         }
     }
 }
diff --git a/src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Convert.FromHexString.cs b/src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Convert.FromHexString.cs
index fd8bcd6c8e05d0..643971e0163962 100644
--- a/src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Convert.FromHexString.cs
+++ b/src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Convert.FromHexString.cs
@@ -42,7 +42,7 @@ private static void TestSequence(byte[] expected, string actual)
             Assert.Equal(OperationStatus.Done, Convert.FromHexString(actual, tryResult, out int consumed, out int written));
             Assert.Equal(fromResult.Length, written);
             Assert.Equal(actual.Length, consumed);
-            AssertExtensions.SequenceEqual(expected, tryResult);
+            AssertExtensions.SequenceEqual(expected.AsSpan(), tryResult);
         }
 
         [Fact]
diff --git a/src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Random.cs b/src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Random.cs
index 27cfa26920e064..d737c8978f52c9 100644
--- a/src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Random.cs
+++ b/src/libraries/System.Runtime/tests/System.Runtime.Extensions.Tests/System/Random.cs
@@ -713,9 +713,9 @@ public static void Shuffle_Array_Seeded(bool emptyShuffle)
             Random random = new Random(0x70636A61);
             int[] items = new int[] { 1, 2, 3, 4 };
             random.Shuffle(items);
-            AssertExtensions.SequenceEqual(stackalloc int[] { 4, 2, 1, 3 }, items);
+            AssertExtensions.SequenceEqual(stackalloc int[] { 4, 2, 1, 3 }, items.AsSpan());
             random.Shuffle(items);
-            AssertExtensions.SequenceEqual(stackalloc int[] { 2, 3, 4, 1 }, items);
+            AssertExtensions.SequenceEqual(stackalloc int[] { 2, 3, 4, 1 }, items.AsSpan());
 
             if (emptyShuffle)
             {
@@ -724,7 +724,7 @@ public static void Shuffle_Array_Seeded(bool emptyShuffle)
             }
 
             random.Shuffle(items);
-            AssertExtensions.SequenceEqual(stackalloc int[] { 1, 4, 3, 2 }, items);
+            AssertExtensions.SequenceEqual(stackalloc int[] { 1, 4, 3, 2 }, items.AsSpan());
         }
 
         [Fact]
@@ -831,13 +831,13 @@ public static void GetItems_Buffer_Seeded()
 
             Span<byte> buffer = stackalloc byte[7];
             random.GetItems(items, buffer);
-            AssertExtensions.SequenceEqual(new byte[] { 3, 1, 3, 2, 3, 3, 3 }, buffer);
+            AssertExtensions.SequenceEqual(new byte[] { 3, 1, 3, 2, 3, 3, 3 }.AsSpan(), buffer);
 
             random.GetItems(items, buffer);
-            AssertExtensions.SequenceEqual(new byte[] { 2, 1, 2, 1, 2, 3, 1 }, buffer);
+            AssertExtensions.SequenceEqual(new byte[] { 2, 1, 2, 1, 2, 3, 1 }.AsSpan(), buffer);
 
             random.GetItems(items, buffer);
-            AssertExtensions.SequenceEqual(new byte[] { 1, 1, 3, 1, 3, 2, 2 }, buffer);
+            AssertExtensions.SequenceEqual(new byte[] { 1, 1, 3, 1, 3, 2, 2 }.AsSpan(), buffer);
         }
 
         private static Random Create(bool derived, bool seeded) =>
diff --git a/src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Runtime/CompilerServices/RuntimeHelpersTests.cs b/src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Runtime/CompilerServices/RuntimeHelpersTests.cs
index 13ce28e4f233cd..8c9f6ea247c580 100644
--- a/src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Runtime/CompilerServices/RuntimeHelpersTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Runtime.Tests/System/Runtime/CompilerServices/RuntimeHelpersTests.cs
@@ -391,10 +391,10 @@ public static void ArrayGetSubArrayTest()
             Assert.Equal(a, RuntimeHelpers.GetSubArray(a, range));
 
             range = new Range(Index.FromStart(1), Index.FromEnd(5));
-            Assert.Equal(new int [] { 2, 3, 4, 5}, RuntimeHelpers.GetSubArray(a, range));
+            Assert.Equal(new int[] { 2, 3, 4, 5 }, RuntimeHelpers.GetSubArray(a, range));
 
             range = new Range(Index.FromStart(0), Index.FromStart(a.Length + 1));
-            Assert.Throws<ArgumentOutOfRangeException>(() => { int [] array = RuntimeHelpers.GetSubArray(a, range); });
+            Assert.Throws<ArgumentOutOfRangeException>(() => { int[] array = RuntimeHelpers.GetSubArray(a, range); });
         }
 
         [Fact]
@@ -454,6 +454,11 @@ private ref struct RefStructWithReferences
         private ref struct RefStructWithRef
         {
             public ref int a;
+
+            internal RefStructWithRef(ref int aVal)
+            {
+                a = ref aVal;
+            }
         }
 
         private ref struct RefStructWithNestedRef
@@ -499,7 +504,7 @@ public static unsafe void SizeOf()
             Assert.Equal(8, RuntimeHelpers.SizeOf(typeof(double).TypeHandle));
             Assert.Equal(3, RuntimeHelpers.SizeOf(typeof(Byte3).TypeHandle));
             Assert.Equal(nint.Size, RuntimeHelpers.SizeOf(typeof(void*).TypeHandle));
-            Assert.Equal(nint.Size, RuntimeHelpers.SizeOf(typeof(delegate* <void>).TypeHandle));
+            Assert.Equal(nint.Size, RuntimeHelpers.SizeOf(typeof(delegate*<void>).TypeHandle));
             Assert.Equal(nint.Size, RuntimeHelpers.SizeOf(typeof(int).MakeByRefType().TypeHandle));
             Assert.Throws<ArgumentNullException>(() => RuntimeHelpers.SizeOf(default));
             Assert.ThrowsAny<ArgumentException>(() => RuntimeHelpers.SizeOf(typeof(List<>).TypeHandle));
diff --git a/src/libraries/System.Runtime/tests/System.Text.Encoding.Tests/Ascii/CaseConversionTests.cs b/src/libraries/System.Runtime/tests/System.Text.Encoding.Tests/Ascii/CaseConversionTests.cs
index ceb836ff268a41..ef06e40d1c2dfd 100644
--- a/src/libraries/System.Runtime/tests/System.Text.Encoding.Tests/Ascii/CaseConversionTests.cs
+++ b/src/libraries/System.Runtime/tests/System.Text.Encoding.Tests/Ascii/CaseConversionTests.cs
@@ -25,20 +25,20 @@ public static void OverlappingBuffers_Throws()
             Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(byteBuffer, byteBuffer, out _));
             Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(byteBuffer.AsSpan(1, 3), byteBuffer.AsSpan(3, 5), out _));
             // byte -> char
-            Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(byteBuffer, MemoryMarshal.Cast<byte, char>(byteBuffer), out _));
-            Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(byteBuffer, MemoryMarshal.Cast<byte, char>(byteBuffer).Slice(1, 3), out _));
-            Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(byteBuffer, MemoryMarshal.Cast<byte, char>(byteBuffer), out _));
-            Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(byteBuffer, MemoryMarshal.Cast<byte, char>(byteBuffer).Slice(1, 3), out _));
+            Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(byteBuffer, MemoryMarshal.Cast<byte, char>(byteBuffer.AsSpan()), out _));
+            Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(byteBuffer, MemoryMarshal.Cast<byte, char>(byteBuffer.AsSpan()).Slice(1, 3), out _));
+            Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(byteBuffer, MemoryMarshal.Cast<byte, char>(byteBuffer.AsSpan()), out _));
+            Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(byteBuffer, MemoryMarshal.Cast<byte, char>(byteBuffer.AsSpan()).Slice(1, 3), out _));
             // char -> char
             Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(charBuffer, charBuffer, out _));
             Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(charBuffer.AsSpan(1, 3), charBuffer.AsSpan(3, 5), out _));
             Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(charBuffer, charBuffer, out _));
             Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(charBuffer.AsSpan(1, 3), charBuffer.AsSpan(3, 5), out _));
             // char -> byte
-            Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(charBuffer, MemoryMarshal.Cast<char, byte>(charBuffer), out _));
-            Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(charBuffer, MemoryMarshal.Cast<char, byte>(charBuffer).Slice(1, 3), out _));
-            Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(charBuffer, MemoryMarshal.Cast<char, byte>(charBuffer), out _));
-            Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(charBuffer, MemoryMarshal.Cast<char, byte>(charBuffer).Slice(1, 3), out _));
+            Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(charBuffer, MemoryMarshal.Cast<char, byte>(charBuffer.AsSpan()), out _));
+            Assert.Throws<InvalidOperationException>(() => Ascii.ToLower(charBuffer, MemoryMarshal.Cast<char, byte>(charBuffer.AsSpan()).Slice(1, 3), out _));
+            Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(charBuffer, MemoryMarshal.Cast<char, byte>(charBuffer.AsSpan()), out _));
+            Assert.Throws<InvalidOperationException>(() => Ascii.ToUpper(charBuffer, MemoryMarshal.Cast<char, byte>(charBuffer.AsSpan()).Slice(1, 3), out _));
         }
 
         private static void VerifySingleChar<T>(OperationStatus status, int value, T expected, T actual, int written)
diff --git a/src/libraries/System.Security.Cryptography.Cose/tests/CoseHeaderValueTests.cs b/src/libraries/System.Security.Cryptography.Cose/tests/CoseHeaderValueTests.cs
index b01cbc953177c4..2d7c891fecf4e6 100644
--- a/src/libraries/System.Security.Cryptography.Cose/tests/CoseHeaderValueTests.cs
+++ b/src/libraries/System.Security.Cryptography.Cose/tests/CoseHeaderValueTests.cs
@@ -97,7 +97,7 @@ public void GetValueAsBytesSucceeds(ContentTestCase @case)
             Span<byte> buffer = new byte[content.Length];
             int length = headerValue.GetValueAsBytes(buffer);
             Assert.Equal(content.Length, length);
-            AssertExtensions.SequenceEqual(content, buffer);
+            AssertExtensions.SequenceEqual(content.AsSpan(), buffer);
         }
 
         [Theory]
@@ -138,7 +138,7 @@ void Verify(int repetitions)
 
                 for (int i = 0; i < expectedLength; i+= content.Length)
                 {
-                    AssertExtensions.SequenceEqual(content, buffer.Slice(i, content.Length));
+                    AssertExtensions.SequenceEqual(content.AsSpan(), buffer.Slice(i, content.Length));
                 }
             }
         }
@@ -244,7 +244,7 @@ public void FromBytesSucceeds(ContentTestCase @case)
 
             Span<byte> buffer = new byte[content.Length];
             int length = headerValue.GetValueAsBytes(buffer);
-            AssertExtensions.SequenceEqual(content, buffer);
+            AssertExtensions.SequenceEqual(content.AsSpan(), buffer);
             Assert.Equal(content.Length, length);
         }
 
diff --git a/src/libraries/System.Security.Cryptography/tests/HashAlgorithmTestDriver.cs b/src/libraries/System.Security.Cryptography/tests/HashAlgorithmTestDriver.cs
index bbcf23ec0e596e..53e6839c5eee42 100644
--- a/src/libraries/System.Security.Cryptography/tests/HashAlgorithmTestDriver.cs
+++ b/src/libraries/System.Security.Cryptography/tests/HashAlgorithmTestDriver.cs
@@ -66,7 +66,7 @@ private void VerifyOneShotStream(Stream input, string output)
             Span<byte> buffer = stackalloc byte[512 / 8];
 
             int written = HashData(input, buffer);
-            AssertExtensions.SequenceEqual(expected, buffer.Slice(0, written));
+            AssertExtensions.SequenceEqual(expected.AsSpan(), buffer.Slice(0, written));
         }
 
         private async Task VerifyOneShotStreamAsync(Stream input, string output)
@@ -75,7 +75,7 @@ private async Task VerifyOneShotStreamAsync(Stream input, string output)
             Memory<byte> buffer = new byte[512 / 8];
 
             int written = await HashDataAsync(input, buffer, cancellationToken: default);
-            AssertExtensions.SequenceEqual(expected, buffer.Slice(0, written).Span);
+            AssertExtensions.SequenceEqual(expected.AsSpan(), buffer.Slice(0, written).Span);
         }
 
         private void VerifyOneShotAllocatingStream(Stream input, string output)
@@ -100,7 +100,7 @@ private void VerifyOneShotStream_CryptographicOperations(Stream input, string ou
             Span<byte> buffer = stackalloc byte[512 / 8];
 
             int written = CryptographicOperations.HashData(HashAlgorithm, input, buffer);
-            AssertExtensions.SequenceEqual(expected, buffer.Slice(0, written));
+            AssertExtensions.SequenceEqual(expected.AsSpan(), buffer.Slice(0, written));
         }
 
         private async Task VerifyOneShotStreamAsync_CryptographicOperations(Stream input, string output)
@@ -114,7 +114,7 @@ private async Task VerifyOneShotStreamAsync_CryptographicOperations(Stream input
                 buffer,
                 cancellationToken: default);
 
-            AssertExtensions.SequenceEqual(expected, buffer.Slice(0, written).Span);
+            AssertExtensions.SequenceEqual(expected.AsSpan(), buffer.Slice(0, written).Span);
         }
 
         private void VerifyOneShotAllocatingStream_CryptographicOperations(Stream input, string output)
diff --git a/src/libraries/System.Security.Cryptography/tests/HmacTests.cs b/src/libraries/System.Security.Cryptography/tests/HmacTests.cs
index 75a36fba2e879e..a2d649fb3d960a 100644
--- a/src/libraries/System.Security.Cryptography/tests/HmacTests.cs
+++ b/src/libraries/System.Security.Cryptography/tests/HmacTests.cs
@@ -136,7 +136,7 @@ protected void VerifyHashDataStream(ReadOnlySpan<byte> key, Stream stream, strin
             int written = HashDataOneShot(key, stream, destination);
 
             Assert.Equal(MacSize, written);
-            AssertExtensions.SequenceEqual(expected, destination);
+            AssertExtensions.SequenceEqual(expected.AsSpan(), destination);
         }
 
         protected void VerifyHashDataStream_CryptographicOperations(ReadOnlySpan<byte> key, Stream stream, string output)
@@ -146,7 +146,7 @@ protected void VerifyHashDataStream_CryptographicOperations(ReadOnlySpan<byte> k
             int written = CryptographicOperations.HmacData(HashAlgorithm, key, stream, destination);
 
             Assert.Equal(MacSize, written);
-            AssertExtensions.SequenceEqual(expected, destination);
+            AssertExtensions.SequenceEqual(expected.AsSpan(), destination);
         }
 
         protected async Task VerifyHashDataStreamAsync(ReadOnlyMemory<byte> key, Stream stream, string output)
@@ -156,7 +156,7 @@ protected async Task VerifyHashDataStreamAsync(ReadOnlyMemory<byte> key, Stream
             int written = await HashDataOneShotAsync(key, stream, destination, cancellationToken: default);
 
             Assert.Equal(MacSize, written);
-            AssertExtensions.SequenceEqual(expected, destination.Span);
+            AssertExtensions.SequenceEqual(expected.AsSpan(), destination.Span);
         }
 
         protected async Task VerifyHashDataStreamAsync_CryptographicOperations(ReadOnlyMemory<byte> key, Stream stream, string output)
@@ -171,7 +171,7 @@ protected async Task VerifyHashDataStreamAsync_CryptographicOperations(ReadOnlyM
                 cancellationToken: default);
 
             Assert.Equal(MacSize, written);
-            AssertExtensions.SequenceEqual(expected, destination.Span);
+            AssertExtensions.SequenceEqual(expected.AsSpan(), destination.Span);
         }
 
         protected void VerifyHashDataStreamAllocating(byte[] key, Stream stream, string output, bool spanKey)
diff --git a/src/libraries/System.Security.Cryptography/tests/KmacTestDriver.cs b/src/libraries/System.Security.Cryptography/tests/KmacTestDriver.cs
index b508acacc1d6d5..4d7c10b317add9 100644
--- a/src/libraries/System.Security.Cryptography/tests/KmacTestDriver.cs
+++ b/src/libraries/System.Security.Cryptography/tests/KmacTestDriver.cs
@@ -500,7 +500,7 @@ public void GetHashAndReset_ResetWithEmpty()
                 mac = stackalloc byte[OutputLength];
                 TKmacTrait.AppendData(kmac, "habaneros"u8);
                 TKmacTrait.GetHashAndReset(kmac, mac);
-                AssertExtensions.SequenceEqual(expected, mac);
+                AssertExtensions.SequenceEqual(expected.AsSpan(), mac);
             }
         }
 
diff --git a/src/libraries/System.Security.Cryptography/tests/X509Certificates/ExtensionsTests/AuthorityKeyIdentifierTests.cs b/src/libraries/System.Security.Cryptography/tests/X509Certificates/ExtensionsTests/AuthorityKeyIdentifierTests.cs
index aea774d4b6968d..d4fa69b979b0fe 100644
--- a/src/libraries/System.Security.Cryptography/tests/X509Certificates/ExtensionsTests/AuthorityKeyIdentifierTests.cs
+++ b/src/libraries/System.Security.Cryptography/tests/X509Certificates/ExtensionsTests/AuthorityKeyIdentifierTests.cs
@@ -477,7 +477,7 @@ public static void CreateFromLargeKeyIdentifier()
 
             byte[] rawData = akid.RawData;
 
-            AssertExtensions.SequenceEqual(keyId, rawData.AsSpan(6));
+            AssertExtensions.SequenceEqual(keyId.AsSpan(), rawData.AsSpan(6));
             Assert.Equal("308183808180", rawData.AsSpan(0, 6).ByteArrayToHex());
         }
 
diff --git a/src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs b/src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs
index dca61c889c89d8..20cdf3775c0a43 100644
--- a/src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs
+++ b/src/libraries/System.Text.Json/src/System/Text/Json/Document/JsonDocument.MetadataDb.cs
@@ -381,7 +381,7 @@ internal MetadataDb CopySegment(int startIndex, int endIndex)
                 byte[] newDatabase = new byte[length];
                 _data.AsSpan(startIndex, length).CopyTo(newDatabase);
 
-                Span<int> newDbInts = MemoryMarshal.Cast<byte, int>(newDatabase);
+                Span<int> newDbInts = MemoryMarshal.Cast<byte, int>(newDatabase.AsSpan());
                 int locationOffset = newDbInts[0];
 
                 // Need to nudge one forward to account for the hidden quote on the string.
diff --git a/src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Memory.cs b/src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Memory.cs
index 58525300624be0..b99428c39c7d6c 100644
--- a/src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Memory.cs
+++ b/src/libraries/System.Text.Json/tests/Common/CollectionTests/CollectionTests.Memory.cs
@@ -34,7 +34,7 @@ public async Task SerializeReadOnlyMemoryOfTAsync()
         public async Task DeserializeMemoryOfTAsync()
         {
             Memory<int> memoryInt = await Serializer.DeserializeWrapper<Memory<int>>("[1,2,3]");
-            AssertExtensions.SequenceEqual(new int[] { 1, 2, 3 }, memoryInt.Span);
+            AssertExtensions.SequenceEqual(new int[] { 1, 2, 3 }.AsSpan(), memoryInt.Span);
 
             Memory<EmptyClass> memoryPoco = new EmptyClass[] { new(), new(), new() }.AsMemory();
             Assert.Equal(3, memoryPoco.Length);
@@ -75,7 +75,7 @@ public async Task DeserializeMemoryOfTClassAsync()
         {
             string json = @"{""Memory"":[1,2,3]}";
             MemoryOfTClass<int> memoryOfIntClass = await Serializer.DeserializeWrapper<MemoryOfTClass<int>>(json);
-            AssertExtensions.SequenceEqual(new int[] { 1, 2, 3 }, memoryOfIntClass.Memory.Span);
+            AssertExtensions.SequenceEqual(new int[] { 1, 2, 3 }.AsSpan(), memoryOfIntClass.Memory.Span);
         }
 
         [Fact]
@@ -97,7 +97,7 @@ public async Task SerializeMemoryByteAsync()
         public async Task DeserializeMemoryByteAsync()
         {
             Memory<byte> memory = await Serializer.DeserializeWrapper<Memory<byte>>("\"VGhpcyBpcyBzb21lIHRlc3QgZGF0YSEhIQ==\"");
-            AssertExtensions.SequenceEqual(s_testData, memory.Span);
+            AssertExtensions.SequenceEqual(s_testData.AsSpan(), memory.Span);
 
             ReadOnlyMemory<byte> readOnlyMemory = await Serializer.DeserializeWrapper<ReadOnlyMemory<byte>>("\"VGhpcyBpcyBzb21lIHRlc3QgZGF0YSEhIQ==\"");
             AssertExtensions.SequenceEqual(s_testData, readOnlyMemory.Span);
@@ -135,7 +135,7 @@ public async Task DeserializeMemoryByteClassAsync()
             string json = @"{""Memory"":""VGhpcyBpcyBzb21lIHRlc3QgZGF0YSEhIQ==""}";
 
             MemoryOfTClass<byte> memoryOfByteClass = await Serializer.DeserializeWrapper<MemoryOfTClass<byte>>(json);
-            AssertExtensions.SequenceEqual<byte>(s_testData, memoryOfByteClass.Memory.Span);
+            AssertExtensions.SequenceEqual<byte>(s_testData.AsSpan(), memoryOfByteClass.Memory.Span);
         }
     }
 }
diff --git a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
index feca0c535edf97..c1a704287c87be 100644
--- a/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
+++ b/src/libraries/System.Text.RegularExpressions/tests/FunctionalTests/UpgradeToGeneratedRegexAnalyzerTests.cs
@@ -85,9 +85,7 @@ public async Task TopLevelStatements(InvocationType invocationType)
             string test = @"using System.Text.RegularExpressions;
 var isMatch = [|" + ConstructRegexInvocation(invocationType, pattern: "\"\"") + @"|]" + isMatchInvocation + ";";
             string fixedCode = @"using System.Text.RegularExpressions;
-var isMatch = MyRegex().IsMatch("""");
-
-partial class Program
+var isMatch = MyRegex().IsMatch(""""); partial class Program
 {
     [GeneratedRegex("""")]
     private static partial Regex MyRegex();
@@ -850,9 +848,7 @@ public async Task TopLevelStatements_MultipleSourceFiles()
                 },
                 FixedState =
                 {
-                    Sources = { "public class C { }", @"var r = MyRegex();
-
-partial class Program
+                    Sources = { "public class C { }", @"var r = MyRegex(); partial class Program
 {
     [System.Text.RegularExpressions.GeneratedRegex("""")]
     private static partial System.Text.RegularExpressions.Regex MyRegex();
diff --git a/src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/CompilerGeneratedCodeAccessedViaReflection.cs b/src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/CompilerGeneratedCodeAccessedViaReflection.cs
index b59683325cdf0d..f46a06eb2debcf 100644
--- a/src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/CompilerGeneratedCodeAccessedViaReflection.cs
+++ b/src/tools/illink/test/Mono.Linker.Tests.Cases/DataFlow/CompilerGeneratedCodeAccessedViaReflection.cs
@@ -63,6 +63,7 @@ public static IEnumerable<int> IteratorWithCorrectDataflow ()
 				t_IteratorWithCorrectDataflow.RequiresAll ();
 			}
 
+			[UnexpectedWarning ("IL2062", Tool.Trimmer | Tool.NativeAot, "https://github.com/dotnet/runtime/issues/110553", CompilerGeneratedCode = true)]
 			public static IEnumerable<int> IteratorWithIntegerDataflow ()
 			{
 				int integerLocal = 0;