Revert "Revert "Avoid creating a result temp for is-expressions (#68694…

…)" (#6…"

This reverts commit b4a9c62.

src/Compilers/CSharp/Portable/BoundTree/BoundLoweredIsPatternExpression.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+
+namespace Microsoft.CodeAnalysis.CSharp;
+
+partial class BoundLoweredIsPatternExpression
+{
+    private partial void Validate()
+    {
+        // Ensure fall-through is unreachable
+        Debug.Assert(this.Statements is [.., BoundGotoStatement or BoundSwitchDispatch]);
+    }
+}

src/Compilers/CSharp/Portable/BoundTree/BoundNodes.xml

@@ -2340,6 +2340,7 @@
          'is not Type t') will need to compensate for negated patterns. IsNegated is set if Pattern is the negated
          form of the inner pattern represented by DecisionDag. -->
   <Node Name="BoundIsPatternExpression" Base="BoundExpression">
+    <Field Name="Type" Type="TypeSymbol" Override="true" Null="disallow"/>
     <Field Name="Expression" Type="BoundExpression" Null="disallow"/>
     <Field Name="Pattern" Type="BoundPattern" Null="disallow"/>
     <Field Name="IsNegated" Type="bool"/>
@@ -2348,6 +2349,13 @@
     <Field Name="WhenFalseLabel" Type="LabelSymbol" Null="disallow"/>
   </Node>
 
+  <Node Name="BoundLoweredIsPatternExpression" Base="BoundExpression" HasValidate="true">
+    <Field Name="Type" Type="TypeSymbol" Override="true" Null="disallow"/>
+    <Field Name="Statements" Type="ImmutableArray&lt;BoundStatement&gt;"/>
+    <Field Name="WhenTrueLabel" Type="LabelSymbol" Null="disallow"/>
+    <Field Name="WhenFalseLabel" Type="LabelSymbol" Null="disallow"/>
+  </Node>
+
   <AbstractNode Name="BoundPattern" Base="BoundNode">
     <Field Name="InputType" Type="TypeSymbol" Null="disallow"/>
     <Field Name="NarrowedType" Type="TypeSymbol" Null="disallow"/>

src/Compilers/CSharp/Portable/CodeGen/EmitExpression.cs

@@ -315,6 +315,10 @@ private void EmitExpressionCore(BoundExpression expression, bool used)
                     EmitRefValueOperator((BoundRefValueOperator)expression, used);
                     break;
 
+                case BoundKind.LoweredIsPatternExpression:
+                    EmitLoweredIsPatternExpression((BoundLoweredIsPatternExpression)expression, used);
+                    break;
+
                 case BoundKind.LoweredConditionalAccess:
                     EmitLoweredConditionalAccessExpression((BoundLoweredConditionalAccess)expression, used);
                     break;
@@ -352,6 +356,42 @@ private void EmitExpressionCore(BoundExpression expression, bool used)
             }
         }
 
+        private void EmitLoweredIsPatternExpression(BoundLoweredIsPatternExpression node, bool used, bool sense = true)
+        {
+            EmitSideEffects(node.Statements);
+
+            if (!used)
+            {
+                _builder.MarkLabel(node.WhenTrueLabel);
+                _builder.MarkLabel(node.WhenFalseLabel);
+            }
+            else
+            {
+                var doneLabel = new object();
+                _builder.MarkLabel(node.WhenTrueLabel);
+                _builder.EmitBoolConstant(sense);
+                _builder.EmitBranch(ILOpCode.Br, doneLabel);
+                _builder.AdjustStack(-1);
+                _builder.MarkLabel(node.WhenFalseLabel);
+                _builder.EmitBoolConstant(!sense);
+                _builder.MarkLabel(doneLabel);
+            }
+        }
+
+        private void EmitSideEffects(ImmutableArray<BoundStatement> statements)
+        {
+#if DEBUG
+            int prevStack = _expectedStackDepth;
+            int origStack = _builder.GetStackDepth();
+            _expectedStackDepth = origStack;
+#endif
+            EmitStatements(statements);
+#if DEBUG
+            Debug.Assert(_expectedStackDepth == origStack);
+            _expectedStackDepth = prevStack;
+#endif
+        }
+
         private void EmitThrowExpression(BoundThrowExpression node, bool used)
         {
             this.EmitThrow(node.Expression);
@@ -830,7 +870,7 @@ private void EmitSequencePoint(BoundSequencePointExpression node)
             }
         }
 
-        private void EmitSequenceExpression(BoundSequence sequence, bool used)
+        private void EmitSequenceExpression(BoundSequence sequence, bool used, bool sense = true)
         {
             DefineLocals(sequence);
             EmitSideEffects(sequence);
@@ -844,7 +884,14 @@ private void EmitSequenceExpression(BoundSequence sequence, bool used)
             Debug.Assert(sequence.Value.Kind != BoundKind.TypeExpression || !used);
             if (sequence.Value.Kind != BoundKind.TypeExpression)
             {
-                EmitExpression(sequence.Value, used);
+                if (used && sequence.Type.SpecialType == SpecialType.System_Boolean)
+                {
+                    EmitCondExpr(sequence.Value, sense: sense);
+                }
+                else
+                {
+                    EmitExpression(sequence.Value, used: used);
+                }
             }
 
             // sequence is used as a value, can release all locals

src/Compilers/CSharp/Portable/CodeGen/EmitOperators.cs

@@ -484,14 +484,25 @@ private void EmitCondExpr(BoundExpression condition, bool sense)
                 return;
             }
 
-            if (condition.Kind == BoundKind.BinaryOperator)
+            switch (condition.Kind)
             {
-                var binOp = (BoundBinaryOperator)condition;
-                if (IsConditional(binOp.OperatorKind))
-                {
+                case BoundKind.BinaryOperator:
+                    var binOp = (BoundBinaryOperator)condition;
+                    if (!IsConditional(binOp.OperatorKind))
+                    {
+                        break;
+                    }
+
                     EmitBinaryCondOperator(binOp, sense);
                     return;
-                }
+
+                case BoundKind.Sequence:
+                    EmitSequenceExpression((BoundSequence)condition, used: true, sense);
+                    return;
+
+                case BoundKind.LoweredIsPatternExpression:
+                    EmitLoweredIsPatternExpression((BoundLoweredIsPatternExpression)condition, used: true, sense);
+                    return;
             }
 
             EmitExpression(condition, true);

src/Compilers/CSharp/Portable/CodeGen/EmitStatement.cs

@@ -24,6 +24,10 @@ namespace Microsoft.CodeAnalysis.CSharp.CodeGen
 {
     internal partial class CodeGenerator
     {
+#if DEBUG
+        private int _expectedStackDepth = 0;
+#endif
+
         private void EmitStatement(BoundStatement statement)
         {
             switch (statement.Kind)
@@ -108,7 +112,7 @@ private void EmitStatement(BoundStatement statement)
 #if DEBUG
             if (_stackLocals == null || _stackLocals.Count == 0)
             {
-                _builder.AssertStackEmpty();
+                _builder.AssertStackDepth(_expectedStackDepth);
             }
 #endif
 
@@ -572,6 +576,28 @@ top.condition is BoundBinaryOperator binary &&
                     }
                     return;
 
+                case BoundKind.LoweredIsPatternExpression:
+                    {
+                        var loweredIs = (BoundLoweredIsPatternExpression)condition;
+                        dest ??= new object();
+
+                        EmitSideEffects(loweredIs.Statements);
+
+                        if (sense)
+                        {
+                            _builder.MarkLabel(loweredIs.WhenTrueLabel);
+                            _builder.EmitBranch(ILOpCode.Br, dest);
+                            _builder.MarkLabel(loweredIs.WhenFalseLabel);
+                        }
+                        else
+                        {
+                            _builder.MarkLabel(loweredIs.WhenFalseLabel);
+                            _builder.EmitBranch(ILOpCode.Br, dest);
+                            _builder.MarkLabel(loweredIs.WhenTrueLabel);
+                        }
+                    }
+                    return;
+
                 case BoundKind.UnaryOperator:
                     var unOp = (BoundUnaryOperator)condition;
                     if (unOp.OperatorKind == UnaryOperatorKind.BoolLogicalNegation)

src/Compilers/CSharp/Portable/CodeGen/Optimizer.cs

@@ -415,6 +415,10 @@ internal sealed class StackOptimizerPass1 : BoundTreeRewriter
 
         private int _recursionDepth;
 
+#if DEBUG
+        private int _expectedStackDepth = 0;
+#endif
+
         private StackOptimizerPass1(Dictionary<LocalSymbol, LocalDefUseInfo> locals,
             ArrayBuilder<ValueTuple<BoundExpression, ExprContext>> evalStack,
             bool debugFriendly)
@@ -565,10 +569,27 @@ private void PopEvalStack()
 
         public BoundNode VisitStatement(BoundNode node)
         {
-            Debug.Assert(node == null || EvalStackIsEmpty());
+#if DEBUG
+            Debug.Assert(node == null || StackDepth() == _expectedStackDepth);
+#endif
             return VisitSideEffect(node);
         }
 
+        public ImmutableArray<BoundStatement> VisitSideEffects(ImmutableArray<BoundStatement> statements)
+        {
+#if DEBUG
+            int prevStack = _expectedStackDepth;
+            int origStack = StackDepth();
+            _expectedStackDepth = origStack;
+#endif
+            var result = this.VisitList(statements);
+#if DEBUG
+            Debug.Assert(_expectedStackDepth == origStack);
+            _expectedStackDepth = prevStack;
+#endif
+            return result;
+        }
+
         public BoundNode VisitSideEffect(BoundNode node)
         {
             var origStack = StackDepth();
@@ -1416,8 +1437,6 @@ public override BoundNode VisitConditionalGoto(BoundConditionalGoto node)
 
         public override BoundNode VisitSwitchDispatch(BoundSwitchDispatch node)
         {
-            Debug.Assert(EvalStackIsEmpty());
-
             // switch dispatch needs a byval local or a parameter as a key.
             // if this is already a fitting local, let's keep it that way
             BoundExpression boundExpression = node.Expression;
@@ -1447,6 +1466,14 @@ public override BoundNode VisitSwitchDispatch(BoundSwitchDispatch node)
             return node.Update(boundExpression, node.Cases, node.DefaultLabel, node.LengthBasedStringSwitchDataOpt);
         }
 
+        public override BoundNode VisitLoweredIsPatternExpression(BoundLoweredIsPatternExpression node)
+        {
+            var statements = VisitSideEffects(node.Statements);
+            RecordBranch(node.WhenTrueLabel);
+            RecordBranch(node.WhenFalseLabel);
+            return node.Update(statements, node.WhenTrueLabel, node.WhenFalseLabel, VisitType(node.Type));
+        }
+
         public override BoundNode VisitConditionalOperator(BoundConditionalOperator node)
         {
             var origStack = StackDepth();

src/Compilers/CSharp/Portable/FlowAnalysis/AbstractFlowPass.cs

@@ -3039,6 +3039,12 @@ public override BoundNode VisitConditionalReceiver(BoundConditionalReceiver node
             return null;
         }
 
+        public override BoundNode VisitLoweredIsPatternExpression(BoundLoweredIsPatternExpression node)
+        {
+            VisitStatements(node.Statements);
+            return null;
+        }
+
         public override BoundNode VisitComplexConditionalReceiver(BoundComplexConditionalReceiver node)
         {
             var savedState = this.State.Clone();