Unsafe.As produces incorrect data with Vectors (in Release)

[benaadams]

Code: https://gist.github.com/benaadams/290f7d5c7b1eb4a97c6854654c7fd6b2

>dotnet run
Unsafe.As           : {X:8.5 Y:9.4 Z:1.2 W:1}
Unsafe.Read         : {X:8.5 Y:9.4 Z:1.2 W:1}
Unsafe.ReadUnaligned: {X:8.5 Y:9.4 Z:1.2 W:1}
No Vectors          : {X:8.5 Y:9.4 Z:1.2 W:1}
Manual Vectors      : {X:8.5 Y:9.4 Z:1.2 W:1}

>dotnet run -c Release
Unsafe.As           : {X:1.256664E-08 Y:0 Z:1.256664E-08 W:0}
Unsafe.Read         : {X:8.5 Y:9.4 Z:1.2 W:1}
Unsafe.ReadUnaligned: {X:8.5 Y:9.4 Z:1.2 W:1}
No Vectors          : {X:8.5 Y:9.4 Z:1.2 W:1}
Manual Vectors      : {X:8.5 Y:9.4 Z:1.2 W:1}

From dotnet/corefx#25510 (comment)

[benaadams]

Maybe simpler repo https://gist.github.com/benaadams/b3270fe6e33a136893e39a5e32ceedc7

>dotnet run
Unsafe.As           : 163.05
Unsafe.Read         : 163.05
Unsafe.ReadUnaligned: 163.05
No Vectors          : 163.05
Manual Vectors      : 163.05

>dotnet run -c Release
Unsafe.As           : 1
Unsafe.Read         : 163.05
Unsafe.ReadUnaligned: 163.05
No Vectors          : 163.05
Manual Vectors      : 163.05

[mikedn]

With a current checked build your latest repro produces an assert in lsra.cpp:

Assert failure(PID 12884 [0x00003254], Thread: 7976 [0x1f28]): Assertion failed '(consume > 1) || (regType(store->gtOp1->TypeGet()) == regType(store->TypeGet()))' in 'UnsafeTesting.Program:LengthSquaredUnsafeAs():float' (IL size 35)

    File: d:\projects\coreclr\src\jit\lsra.cpp Line: 3800
    Image: D:\Projects\coreclr\bin\Product\Windows_NT.x64.Checked\CoreRun.exe

And the relevant piece of IR is:

N001 (  3,  2) [000070] -------N----        t70 =    LCL_VAR   struct(P) V00 loc0         
                                                  *    float  V00.X (offs=0x00) -> V03 tmp2         
                                                  *    float  V00.Y (offs=0x04) -> V04 tmp3         
                                                  *    float  V00.Z (offs=0x08) -> V05 tmp4         
                                                  *    float  V00.W (offs=0x0c) -> V06 tmp5          $140
                                                 /--*  t70    struct 
N003 (  3,  3) [000056] DA--G-------              *  STORE_LCL_VAR simd16 V01 tmp0         d:3

[CarolEidt]

This has apparently slipped through the cracks. I'll take a look.

[benaadams]

Seem to still be getting bad results dotnet/corefx#25510 (comment)

at System.Numerics.Tests.QuaternionTests.QuaternionAddTest()
 in System.Numerics.Vectors\tests\QuaternionTests.cs:line 545
Assert.Equal() Failure
Expected: {X:6 Y:8 Z:10 W:12}
Actual:   {X:2.978865E-34 Y:5 Z:6 W:7}

public static Quaternion Add(Quaternion value1, Quaternion value2)
{
    Vector4 q1 = Unsafe.As<Quaternion, Vector4>(ref value1);
    Vector4 q2 = Unsafe.As<Quaternion, Vector4>(ref value2);

    Vector4 result = q1 + q2;

    return Unsafe.As<Vector4, Quaternion>(ref result);
}

public void QuaternionAddTest()
{
    Quaternion a = new Quaternion(1.0f, 2.0f, 3.0f, 4.0f);
    Quaternion b = new Quaternion(5.0f, 6.0f, 7.0f, 8.0f);

    Quaternion expected = new Quaternion(6.0f, 8.0f, 10.0f, 12.0f);
    Quaternion actual;

    actual = Quaternion.Add(a, b);
    Assert.Equal(expected, actual);
}

[benaadams]

Could it be similar to https://github.com/dotnet/coreclr/issues/16210 ?

[benaadams]

@CarolEidt should I open a new issue?

[CarolEidt]

@CarolEidt should I open a new issue?

Yes, I think that would be best.

[benaadams]

Opened https://github.com/dotnet/coreclr/issues/16254