`INumber.MinNumber` and `INumber.MaxNumber` return `NaN` in `Release` configuration

[PavielKraskouski]

Description

When running a program in Release configuration, INumber.MinNumber and INumber.MaxNumber return NaN if one of the numbers is not NaN. In Debug configuration these methods work as expected.

Reproduction Steps

1. Create a new console project, specify .NET 8 as the target platform.
2. Add the following code:

int numbers = 0;
int NaN = 0;

for (int i = 0; i < 100000; i++)
{
    float minLength = 0;
    float maxLength = 0;

    if (!float.IsNaN(float.MaxNumber(maxLength / minLength, 1)))
    {
        numbers++;
    }
    else
    {
        NaN++;
    }
}

Console.WriteLine($"Numbers: {numbers}");
Console.WriteLine($"NaN: {NaN}");

3. Run the program.

Expected behavior

The output of the program should be as follows:

Numbers: 100000
NaN: 0

Actual behavior

Here is the result of the program in Release configuration:

Numbers: 9999
NaN: 90001

Regression?

The bug could not be reproduced in .NET 7. The program works as expected in both configurations.

Known Workarounds

You can use INumberBase.MinMagnitudeNumber and INumberBase.MaxMagnitudeNumber if you intend to work with only positive numbers.

Configuration

.NET:
Microsoft .NET SDK 8.0.101 (x64) from Visual Studio (8.1.123.58017)
Microsoft .NET SDK 8.0.200-preview.23624.5 (x64) from Visual Studio (8.2.23.62405)

OS:
Windows 11 Pro 23H2 22631.3085
Windows 11 Pro 22H2 22621.3085

Architecture:
x64
x64

Other information

The bug is not reproduced if you replace the first argument of MaxNumber with one of the following:

if (!float.IsNaN(float.MaxNumber(0f / 0f, 1)))
{
    numbers++;
}
else
{
    NaN++;
}

if (!float.IsNaN(float.MaxNumber(float.NaN, 1)))
{
    numbers++;
}
else
{
    NaN++;
}

If we run the code in SharpLab and Compiler Explorer, we get 100,000 NaN. On my machines I get 9,999 numbers and 90,001 NaN.

Tagging subscribers to this area: @dotnet/area-system-numerics
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

When running a program in Release configuration, INumber.MinNumber and INumber.MaxNumber return NaN if one of the numbers is not NaN. In Debug configuration these methods work as expected.

Reproduction Steps

1. Create a new console project, specify .NET 8 as the target platform.
2. Add the following code:

int numbers = 0;
int NaN = 0;

for (int i = 0; i < 100000; i++)
{
    float minLength = 0;
    float maxLength = 0;

    if (!float.IsNaN(float.MaxNumber(maxLength / minLength, 1)))
    {
        numbers++;
    }
    else
    {
        NaN++;
    }
}

Console.WriteLine($"Numbers: {numbers}");
Console.WriteLine($"NaN: {NaN}");

3. Run the program.

Expected behavior

The output of the program should be as follows:

Numbers: 100000
NaN: 0

Actual behavior

Here is the result of the program in Release configuration:

Numbers: 9999
NaN: 90001

Regression?

The bug could not be reproduced in .NET 7. The program works as expected in both configurations.

Known Workarounds

You can use INumberBase.MinMagnitudeNumber and INumberBase.MaxMagnitudeNumber if you intend to work with only positive numbers.

Configuration

.NET:
Microsoft .NET SDK 8.0.101 (x64) from Visual Studio (8.1.123.58017)
Microsoft .NET SDK 8.0.200-preview.23624.5 (x64) from Visual Studio (8.2.23.62405)

OS:
Windows 11 Pro 23H2 22631.3085
Windows 11 Pro 22H2 22621.3085

Architecture:
x64
x64

Other information

The bug is not reproduced if you replace the first argument of MaxNumber with one of the following:

if (!float.IsNaN(float.MaxNumber(0f / 0f, 1)))
{
    numbers++;
}
else
{
    NaN++;
}

if (!float.IsNaN(float.MaxNumber(float.NaN, 1)))
{
    numbers++;
}
else
{
    NaN++;
}

If we run the code in SharpLab and Compiler Explorer, we get 100,000 NaN. On my machines I get 9999 numbers and 90001 NaN.

Author:	PavielKraskouski
Assignees:	-
Labels:	area-System.Numerics, untriaged
Milestone:	-

[MichalPetryka]

With TieredCompilation=0 this gives 100000 NaNs, looks like this is a bug in optimized code.

[EgorBo]

Looks like a codegen bug - when jit compiles float.MaxNumber(x, 1f) it imports it as MAXSS(1f, x) while it should be MAXSS(x, 1f). Because if the 1st argument of MAXSS is NaN - it returns the 2nd argument (1f). If the 2nd argument is NaN - it returns NaN.

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

Issue Details

---

Description

When running a program in Release configuration, INumber.MinNumber and INumber.MaxNumber return NaN if one of the numbers is not NaN. In Debug configuration these methods work as expected.

Reproduction Steps

1. Create a new console project, specify .NET 8 as the target platform.
2. Add the following code:

int numbers = 0;
int NaN = 0;

for (int i = 0; i < 100000; i++)
{
    float minLength = 0;
    float maxLength = 0;

    if (!float.IsNaN(float.MaxNumber(maxLength / minLength, 1)))
    {
        numbers++;
    }
    else
    {
        NaN++;
    }
}

Console.WriteLine($"Numbers: {numbers}");
Console.WriteLine($"NaN: {NaN}");

3. Run the program.

Expected behavior

The output of the program should be as follows:

Numbers: 100000
NaN: 0

Actual behavior

Here is the result of the program in Release configuration:

Numbers: 9999
NaN: 90001

Regression?

The bug could not be reproduced in .NET 7. The program works as expected in both configurations.

Known Workarounds

You can use INumberBase.MinMagnitudeNumber and INumberBase.MaxMagnitudeNumber if you intend to work with only positive numbers.

Configuration

.NET:
Microsoft .NET SDK 8.0.101 (x64) from Visual Studio (8.1.123.58017)
Microsoft .NET SDK 8.0.200-preview.23624.5 (x64) from Visual Studio (8.2.23.62405)

OS:
Windows 11 Pro 23H2 22631.3085
Windows 11 Pro 22H2 22621.3085

Architecture:
x64
x64

Other information

The bug is not reproduced if you replace the first argument of MaxNumber with one of the following:

if (!float.IsNaN(float.MaxNumber(0f / 0f, 1)))
{
    numbers++;
}
else
{
    NaN++;
}

if (!float.IsNaN(float.MaxNumber(float.NaN, 1)))
{
    numbers++;
}
else
{
    NaN++;
}

If we run the code in SharpLab and Compiler Explorer, we get 100,000 NaN. On my machines I get 9,999 numbers and 90,001 NaN.

Author:	PavielKraskouski
Assignees:	EgorBo
Labels:	area-System.Numerics, area-CodeGen-coreclr
Milestone:	-

[tannergooding]

We should also validate this works correctly for MinNumber.

We're supposed to have tests validating the configs here, so I wonder if they aren't getting run in the TieredCompilation=0 outerloop?

[tannergooding]

The issue is this line here: https://github.com/dotnet/runtime/blob/main/src/coreclr/jit/importercalls.cpp#L8520

We setup op1 = cnsNode and op2 = otherNode as required for Max and Min, we then need to swap them if isNumber is true, but because we do std::swap(op1, op2) and then inverse the assignments to retNode, we're just assigning back the original values.

Removing that std::swap(op1, op2) will cause the right thing to happen and fix it 🤦

[MichalPetryka]

Worth noting there's a codegen quality regression here too where the isNaN was folded to constant true on .net 7 but isn't anymore since .net 8.

[tannergooding]

Code quality changes won't meet the backport bar. It's something we can ensure is re-handled for .NET 9.

It likely happened due to using x != x instead of BitConverter, which is ultimately better for the more common non-constant scenarios.