Assertion failed '!(checkUnusedValues && def->IsUnusedValue()) && "operands should never be marked as unused values"' during 'Lowering nodeinfo'

[kunalspathak]

superpmi collection

unused_value.zip

// Found by Antigen
// Reduced from 50.68 KB to 1.71 KB.


using System.Runtime.Intrinsics;
using System.Runtime.Intrinsics.X86;
public class TestClass
{
    static Vector512<double> s_v512_double_51 = Vector512.Create(5.033707865168539);
    Vector512<double> v512_double_113 = Vector512.Create(-1.8461538461538463, 0, -4.942857142857143, 3.0576923076923075, 0.06382978723404255, -1.9444444444444444, 3.1363636363636362, 5.2105263157894735);
    public void Method0()
    {
        unchecked
        {
            byte byte_221 = 0;
            s_v512_double_51 = Avx512F.TernaryLogic(v512_double_113, v512_double_113, v512_double_113, byte_221);
            return;
        }
    }
    public static void Main(string[] args)
    {
        new TestClass().Method0();
    }
}
/*
Environment:

set DOTNET_TieredCompilation=0

JIT assert failed:
Assertion failed '!(checkUnusedValues && def->IsUnusedValue()) && "operands should never be marked as unused values"' in 'TestClass:Method0():this' during 'Lowering nodeinfo' (IL size 379; hash 0x46e9aa75; FullOpts)

    File: D:\a\_work\1\s\src\coreclr\jit\lir.cpp Line: 1649


*/

[dotnet-policy-service]

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

[kunalspathak]

Antigen is hitting this issue a lot of times.

[kunalspathak]

We have V26 = TernaryLogic(...) at one point, but we find out that it is a dead store, so we remove Store(V26), but retain TernaryLogic because we think there is a side effect (need to find out why).

               [000103] DACXG------                         ▌  STORE_LCL_VAR simd64 V26 tmp6         
               [000102] --CXG------                         └──▌  HWINTRINSIC simd64 64 uint TernaryLogic
               [000068] -----------                            ├──▌  LCL_VAR   simd64 V24 tmp4         
               [000094] ---XG------                            ├──▌  HWINTRINSIC simd64 64 ubyte Subtract
               [000090] ---XG------                            │  ├──▌  HWINTRINSIC simd64 64 ubyte Add
               [000074] -----------                            │  │  ├──▌  LCL_VAR   simd64<System.Runtime.Intrinsics.Vector512`1> V19 loc10        
               [000089] ---XG------                            │  │  └──▌  HWINTRINSIC simd64 64 ubyte Subtract
               [000079] -----------                            │  │     ├──▌  LCL_VAR   simd64 V25 tmp5         
               [000088] ---XG------                            │  │     └──▌  HWINTRINSIC simd64 64 uint Xor
               [000084] n---G------                            │  │        ├──▌  IND       simd64
               [000083] H----------                            │  │        │  └──▌  CNS_INT(h) long   0x15200003178 static Fseq[<unknown field>]
               [000087] n--XG------                            │  │        └──▌  IND       simd64
               [000086] ---X-------                            │  │           └──▌  FIELD_ADDR byref  <unknown class>:<unknown field>
               [000085] -----------                            │  │              └──▌  LCL_VAR   ref    V00 this         
               [000093] n--XG------                            │  └──▌  IND       simd64
               [000092] ---X-------                            │     └──▌  FIELD_ADDR byref  <unknown class>:<unknown field>
               [000091] -----------                            │        └──▌  LCL_VAR   ref    V00 this         
               [000097] n--XG------                            ├──▌  IND       simd64
               [000096] ---X-------                            │  └──▌  FIELD_ADDR byref  <unknown class>:<unknown field>
               [000095] -----------                            │     └──▌  LCL_VAR   ref    V00 this         
               [000101] n----------                            └──▌  IND       ubyte 
               [000100] -----------                               └──▌  FIELD_ADDR byref  <unknown class>:byte_0
               [000099] -----------                                  └──▌  LCL_ADDR  byref  V17 loc8         [+0]
                                                                        ▌    ubyte  field V17.byte_0 (fldOffset=0x0) -> V57 tmp37        
                                                                        ▌    long   field V17.ulong_1 (fldOffset=0x8) -> V58 tmp38        

...
Store [000103] is dead but has side effects. Replacing with:

               [000102] --CXG------                         ▌  HWINTRINSIC simd64 64 uint TernaryLogic
               [000068] -----------                         ├──▌  LCL_VAR   simd64 V24 tmp4         
               [000094] ---XG------                         ├──▌  HWINTRINSIC simd64 64 ubyte Subtract
               [000090] ---XG------                         │  ├──▌  HWINTRINSIC simd64 64 ubyte Add
               [000074] -----------                         │  │  ├──▌  LCL_VAR   simd64<System.Runtime.Intrinsics.Vector512`1> V19 loc10        
               [000089] ---XG------                         │  │  └──▌  HWINTRINSIC simd64 64 ubyte Subtract
               [000079] -----------                         │  │     ├──▌  LCL_VAR   simd64 V25 tmp5         
               [000088] ---XG------                         │  │     └──▌  HWINTRINSIC simd64 64 uint Xor
               [000084] n---G------                         │  │        ├──▌  IND       simd64
               [000083] H----------                         │  │        │  └──▌  CNS_INT(h) long   0x15200003178 static Fseq[<unknown field>]
               [000087] n--XG------                         │  │        └──▌  IND       simd64
               [000086] ---X-------                         │  │           └──▌  FIELD_ADDR byref  <unknown class>:<unknown field>
               [000085] -----------                         │  │              └──▌  LCL_VAR   ref    V00 this         
               [000093] n--XG------                         │  └──▌  IND       simd64
               [000092] ---X-------                         │     └──▌  FIELD_ADDR byref  <unknown class>:<unknown field>
               [000091] -----------                         │        └──▌  LCL_VAR   ref    V00 this         
               [000097] n--XG------                         ├──▌  IND       simd64
               [000096] ---X-------                         │  └──▌  FIELD_ADDR byref  <unknown class>:<unknown field>
               [000095] -----------                         │     └──▌  LCL_VAR   ref    V00 this         
               [000101] -----------                         └──▌  LCL_VAR   ubyte  V57 tmp37  

During rationalizer, we mark the [000102] as unused, but do not mark the operands as such.

N001 (  1,  1) [000068] -----+-----                   t68 =    LCL_VAR   simd64 V24 tmp4         u:2 (last use) <l:$544, c:$545>
N002 (  1,  1) [000549] -----------                  t549 =    LCL_VAR   simd64 V63 cse0         u:1 <l:$240, c:$542>
N003 (  1,  1) [000550] -----------                  t550 =    LCL_VAR   simd64 V63 cse0         u:1 <l:$240, c:$542>
N004 (  1,  1) [000101] -----+-N---                  t101 =    CNS_INT   int    0 $40
                                                            ┌──▌  t68    simd64 
                                                            ├──▌  t549   simd64 
                                                            ├──▌  t550   simd64 
                                                            ├──▌  t101   int    
N005 (  5,  5) [000102] ----G+-----                  u102 = ▌  HWINTRINSIC simd64 64 uint TernaryLogic $4d7

We continue to lower the [000102] node and mark it as unused. During CheckLIR, we check the operand t62 and see it is marked as unused and complain about it in the assert above. I am surprised that all the way through, we never check if [000102] was also unused (even in lowering).