Add a hidden sequence point around the code that assigns pattern variables in switch (#14790)

Fixes #14740

src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter_PatternSwitchStatement.cs

@@ -371,35 +371,28 @@ private void LowerConstantValueDecision(DecisionTree.ByValue byValue)
             /// that binds the pattern variables.
             /// </summary>
             /// <param name="bindings">The source/destination pairs for the assignments</param>
-            private BoundStatement BindingsForCase(
-                ImmutableArray<KeyValuePair<BoundExpression, BoundExpression>> bindings)
+            /// <param name="addBindings">A builder to which the label and binding assignments are added</param>
+            private void AddBindingsForCase(
+                ImmutableArray<KeyValuePair<BoundExpression, BoundExpression>> bindings,
+                ArrayBuilder<BoundStatement> addBindings)
             {
                 var patternMatched = _factory.GenerateLabel("patternMatched");
                 _loweredDecisionTree.Add(_factory.Goto(patternMatched));
 
-                var addBindings = ArrayBuilder<BoundStatement>.GetInstance();
+                // Hide the code that binds pattern variables in a hidden sequence point
+                addBindings.Add(_factory.HiddenSequencePoint());
                 addBindings.Add(_factory.Label(patternMatched));
                 if (!bindings.IsDefaultOrEmpty)
                 {
                     foreach (var kv in bindings)
                     {
-                        var source = kv.Key;
-                        var dest = kv.Value;
-                        var rewriter = _localRewriter;
+                        var loweredRight = kv.Key;
+                        var loweredLeft = kv.Value;
                         addBindings.Add(_factory.ExpressionStatement(
-                        rewriter.MakeStaticAssignmentOperator(
-                            _factory.Syntax, rewriter.VisitExpression(dest), rewriter.VisitExpression(source), RefKind.None, dest.Type, false)));
+                            _localRewriter.MakeStaticAssignmentOperator(
+                                _factory.Syntax, loweredLeft, loweredRight, RefKind.None, loweredLeft.Type, false)));
                     }
                 }
-
-                BoundStatement result = _factory.Block(addBindings.ToImmutableAndFree());
-                if (_localRewriter.Instrument)
-                {
-                    // Hide the code that binds pattern variables in a hidden sequence point
-                    result = _localRewriter._instrumenter.InstrumentPatternSwitchBindCasePatternVariables(result);
-                }
-
-                return result;
             }
 
             private void LowerDecisionTree(DecisionTree.Guarded guarded)
@@ -418,14 +411,14 @@ private void LowerDecisionTree(DecisionTree.Guarded guarded)
                     else
                     {
                         // with bindings
-                        sectionBuilder.Add(BindingsForCase(guarded.Bindings));
+                        AddBindingsForCase(guarded.Bindings, sectionBuilder);
                         sectionBuilder.Add(_factory.Goto(targetLabel));
                     }
                 }
                 else
                 {
-                    sectionBuilder.Add(BindingsForCase(guarded.Bindings));
-                    var guardTest = _factory.ConditionalGoto(_localRewriter.VisitExpression(guarded.Guard), targetLabel, true);
+                    AddBindingsForCase(guarded.Bindings, sectionBuilder);
+                    var guardTest = _factory.ConditionalGoto(guarded.Guard, targetLabel, true);
 
                     // Only add instrumentation (such as a sequence point) if the node is not compiler-generated.
                     if (!guarded.Guard.WasCompilerGenerated && _localRewriter.Instrument)