fsharp code gives incorrect result in .NET 6 when compiled in release.

[sylvainouel]

The following code:

open System
type T2 () =
    member this.f b =
        if b = Unchecked.defaultof<Guid> then 
            failwith "Houlala gross problem!"
        else
            hash(b)

[<EntryPoint>]
let main args =
    try
        T2().f (Guid.NewGuid()) |> ignore
    with e -> printfn "%s" e.Message
    0

in the following project:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <Compile Include="Program.fs" />
  </ItemGroup>

</Project>

gives an incorrect output when compiled in release. The exception is thrown.
The correct output is given when program is compiled in debug (eixt status of 0 without any output) or when compiled targeting .NET 5.

dotnet info output is:

dotnet --info
.NET SDK (reflecting any global.json):
Version: 6.0.100
Commit: 9e8b04bbff

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\6.0.100\

Host (useful for support):
Version: 6.0.0
Commit: 4822e3c

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Issue Details

---

The following code:

open System
type T2 () =
    member this.f b =
        if b = Unchecked.defaultof<Guid> then 
            failwith "Houlala gross problem!"
        else
            hash(b)

[<EntryPoint>]
let main args =
    try
        T2().f (Guid.NewGuid()) |> ignore
    with e -> printfn "%s" e.Message
    0

in the following project:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <Compile Include="Program.fs" />
  </ItemGroup>

</Project>

gives an incorrect output when compiled in release. The exception is thrown.
The correct output is given when program is compiled in debug (eixt status of 0 without any output) or when compiled targeting .NET 5.

dotnet info output is:

dotnet --info
.NET SDK (reflecting any global.json):
Version: 6.0.100
Commit: 9e8b04bbff

Runtime Environment:
OS Name: Windows
OS Version: 10.0.18363
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\6.0.100\

Host (useful for support):
Version: 6.0.0
Commit: 4822e3c

Author:	sylvainouel
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-

[sylvainouel]

Further simplification:

open System
let f b =
    if b = Unchecked.defaultof<Guid> then 
        failwith "Houlala gross problem!"
    else
        hash(b)

[<EntryPoint>]
let main args =
    try
        f (Guid.NewGuid()) |> ignore
    with e -> printfn "%s" e.Message
    0

[jakobbotsch]

Looks like in .NET 6 we miss a zero-init of xmm0, but it does not repro in .NET 7. I bisected it to #58410.
cc @BruceForstall, potential backport candidate?

[mrange]

This might be obvious to everyone but FYI I tested in x64 and x86 and the issue reproduced in x64 but not in x86. That could be a potential workaround if you are hit by this issue then.

[akoeplinger]

Fixed by the backport in #62207