Snapshot of working status

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

@@ -110,7 +110,7 @@ private void LowerDecisionTree(DecisionTree.ByType byType, HashSet<LabelSymbol>
                 BoundExpression notNull = byType.Type.IsNullableType()
                     ? this.RewriteNullableNullEquality(_factory.Syntax, BinaryOperatorKind.NullableNullNotEqual, byType.Expression, nullValue, _factory.SpecialType(SpecialType.System_Boolean))
                     : _factory.ObjectNotEqual(byType.Expression, nullValue);
-                result.Add(_factory.If(notNull, _factory.Goto(notNullLabel)));
+                result.Add(_factory.ConditionalGoto(notNull, notNullLabel, true));
                 LowerDecisionTree(byType.WhenNull, usedLabels, usedTemps, result);
                 result.Add(_factory.Goto(defaultLabel));
                 result.Add(_factory.Label(notNullLabel));
@@ -125,8 +125,8 @@ private void LowerDecisionTree(DecisionTree.ByType byType, HashSet<LabelSymbol>
                 var type = td.Key;
                 var decision = td.Value;
                 var failLabel = _factory.GenerateLabel("failedDecision");
-                grep("if there is a fresh temp needed, copy to it and add the temp from ", decision.Expression, " to ", usedTemps);
-                grep("test for the type ", type, " into that temp and goto failLabel when that fails");
+                var testAndCopy = TypeTestAndCopyToTemp(byType.Expression, decision.Expression);
+                result.Add(_factory.ConditionalGoto(testAndCopy, failLabel, false));
                 LowerDecisionTree(decision, usedLabels, usedTemps, result);
                 result.Add(_factory.Label(failLabel));
             }
@@ -135,6 +135,18 @@ private void LowerDecisionTree(DecisionTree.ByType byType, HashSet<LabelSymbol>
             LowerDecisionTree(byType.Default, usedLabels, usedTemps, result);
         }
 
+        private BoundExpression TypeTestAndCopyToTemp(BoundExpression input, BoundExpression temp)
+        {
+            if (input == temp)
+            {
+                // if the expression is the same, no need to type test and copy to temp
+                return _factory.Literal(true);
+            }
+
+            Debug.Assert(temp.Kind == BoundKind.Local);
+            return MakeDeclarationPattern(_factory.Syntax, input, ((BoundLocal)temp).LocalSymbol);
+        }
+
         private void LowerDecisionTree(DecisionTree.ByValue byValue, HashSet<LabelSymbol> usedLabels, HashSet<LocalSymbol> usedTemps, ArrayBuilder<BoundStatement> result)
         {
             throw new NotImplementedException();

src/Compilers/CSharp/Portable/Lowering/SyntheticBoundNodeFactory.cs

@@ -646,6 +646,11 @@ public BoundStatement If(BoundExpression condition, BoundStatement thenClause, B
             return If(condition, ImmutableArray<LocalSymbol>.Empty, thenClause, elseClauseOpt);
         }
 
+        public BoundStatement ConditionalGoto(BoundExpression condition, LabelSymbol label, bool jumpIfTrue)
+        {
+            return new BoundConditionalGoto(Syntax, condition, jumpIfTrue, label) { WasCompilerGenerated = true };
+        }
+
         public BoundStatement If(BoundExpression condition, ImmutableArray<LocalSymbol> locals, BoundStatement thenClause, BoundStatement elseClauseOpt = null)
         {
             // We translate
@@ -668,7 +673,7 @@ public BoundStatement If(BoundExpression condition, ImmutableArray<LocalSymbol>
             {
                 var alt = new GeneratedLabelSymbol("alternative");
 
-                statements.Add(new BoundConditionalGoto(Syntax, condition, false, alt) { WasCompilerGenerated = true });
+                statements.Add(ConditionalGoto(condition, alt, false));
                 statements.Add(thenClause);
                 statements.Add(Goto(afterif));
                 if (!locals.IsDefaultOrEmpty)
@@ -683,7 +688,7 @@ public BoundStatement If(BoundExpression condition, ImmutableArray<LocalSymbol>
             }
             else
             {
-                statements.Add(new BoundConditionalGoto(Syntax, condition, false, afterif) { WasCompilerGenerated = true });
+                statements.Add(ConditionalGoto(condition, afterif, false));
                 statements.Add(thenClause);
                 if (!locals.IsDefaultOrEmpty)
                 {
@@ -697,34 +702,6 @@ public BoundStatement If(BoundExpression condition, ImmutableArray<LocalSymbol>
             return Block(statements.ToImmutableAndFree());
         }
 
-        public BoundStatement For(BoundExpression initialization, BoundExpression termination, BoundExpression increment, BoundStatement body)
-        {
-            //      for(<initialization>; <increment>; <termination>)
-            //      {
-            //          <body>;
-            //      }
-
-            //  Lowered form:
-
-            //      <initialization>;
-            //      goto LoopCondition;
-            //      LoopStart:
-            //      <body>
-            //      <increment>
-            //      LoopCondition:
-            //      if(<termination>)
-            //          goto LoopStart;
-            var lLoopStart = GenerateLabel("LoopStart");
-            var lLoopCondition = GenerateLabel("LoopCondition");
-            return Block(ExpressionStatement(initialization),
-                         Goto(lLoopCondition),
-                         Label(lLoopStart),
-                         body,
-                         ExpressionStatement(increment),
-                         Label(lLoopCondition),
-                         If(termination, Goto(lLoopStart)));
-        }
-
         public BoundThrowStatement Throw(BoundExpression e = null)
         {
             return new BoundThrowStatement(Syntax, e) { WasCompilerGenerated = true };