InvalidProgramException with System.Linq.Expressions and user-defined conditional operators

[MarkMpn]

Description

Using System.Linq.Expressions to build expression trees dynamically, the repro code worked as expected in .NET Framework but fails in .NET (tested .NET 6 & .NET 8)

So far I've managed to narrow this down to when I'm using a type that implements custom conditional operators (true, false, & and |) and using a TryCatch expression on the right hand side of the conditional logic operator (AndAlso or OrElse). If I reorder the arguments so the TryCatch expression is on the left hand side of the operator it works as expected.

Reproduction Steps

using System.Data.SqlTypes;
using System.Linq.Expressions;

var expr = Expression.OrElse(
    Expression.Constant(SqlBoolean.True),
    Expression.TryCatch(
        Expression.Constant(SqlBoolean.True),
        Expression.Catch(
            typeof(SqlTypeException),
            Expression.Constant(SqlBoolean.False)
        )
    )
);
var lambda = Expression.Lambda<Func<SqlBoolean>>(expr);
var func = lambda.Compile();
Console.WriteLine(func());

Expected behavior

The expression should compile and True should be printed to the console.

Actual behavior

A System.InvalidProgramException is thrown by lambda.Compile()

Regression?

Yes - this same code runs as expected in .NET Framework 4.6.2 and 4.8

Known Workarounds

No response

Configuration

.NET 6 and .NET 8
Windows 11 22631.3593
x64
Doesn't appear to be specific to this.

Other information

No response

[dotnet-policy-service]

Tagging subscribers to this area: @cston
See info in area-owners.md if you want to be subscribed.

[EgorBo]

I presume in C# it would look like condition || try { ... . Checked JIT reports your snippet as an invalid program due to:

Evaluation stack must be empty on entry into a try block

My understanding that it is an expected behavior according to ECMA-335 I.12.4.2.8.1 Fall Through:

Entry to protected blocks can be accomplished by fall-through, at which time the evaluation
stack shall be empty.

so I am not sure why and how it used to work in .NET Framework.

so the TryCatch expression is on the left hand side of the operator it works as expected.

if it's on the left side then the evaluation stack is empty

cc @jkotas

[jkotas]

I am not sure why and how it used to work in .NET Framework.

The IL produced by the expression compiler on .NET Framework has an extra spill to make the stack empty. It looks like a regression in System.Linq.Expressions to me.

[jkotas]

Note that we merged a ton of optimizations in S.L.Expressions in the early .NET Core days: https://github.com/dotnet/corefx/pulls?q=label%3Aarea-System.Linq.Expressions+is%3Aclosed+optimize . It is likely one of those of changes.

[jkotas]

It's the changes in LambdaCompiler.EmitMethodAndAlso and LambdaCompiler.EmitMethodOrElse in this commit: 2ecfbbd

cc @VSadov