JIT: Invalid result computed with modulo operation

[jakobbotsch]

// Generated by Fuzzlyn v1.5 on 2022-07-03 14:40:52
// Run on Arm64 MacOS
// Seed: 5960657379714964908
// Reduced from 328.5 KiB to 0.8 KiB in 00:02:08
// Debug: Outputs 0
// Release: Outputs 1
public struct S0
{
    public long F0;
    public long F1;
    public S0(long f1): this()
    {
        F1 = f1;
    }
}

public struct S1
{
    public uint F1;
    public ushort F2;
    public S0 F4;
    public S1(ulong f5): this()
    {
    }

    public long M82(ref short[] arg0)
    {
        Program.s_13 = this.F1++;
        S1 var1 = new S1(0);
        return Program.s_39[0].F1;
    }
}

public class Program
{
    public static uint s_13;
    public static short[] s_28;
    public static S0[] s_39;
    public static void Main()
    {
        S0[] vr2 = new S0[]{new S0(-1)};
        s_39 = vr2;
        S1 vr3 = default(S1);
        M80(vr3);
    }

    public static void M80(S1 arg0)
    {
        arg0.F2 += (ushort)(arg0.F1 % (uint)arg0.M82(ref s_28));
        System.Console.WriteLine(arg0.F2);
    }
}

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

Issue Details

---

// Generated by Fuzzlyn v1.5 on 2022-07-03 14:40:52
// Run on Arm64 MacOS
// Seed: 5960657379714964908
// Reduced from 328.5 KiB to 0.8 KiB in 00:02:08
// Debug: Outputs 0
// Release: Outputs 1
public struct S0
{
    public long F0;
    public long F1;
    public S0(long f1): this()
    {
        F1 = f1;
    }
}

public struct S1
{
    public uint F1;
    public ushort F2;
    public S0 F4;
    public S1(ulong f5): this()
    {
    }

    public long M82(ref short[] arg0)
    {
        Program.s_13 = this.F1++;
        S1 var1 = new S1(0);
        return Program.s_39[0].F1;
    }
}

public class Program
{
    public static uint s_13;
    public static short[] s_28;
    public static S0[] s_39;
    public static void Main()
    {
        S0[] vr2 = new S0[]{new S0(-1)};
        s_39 = vr2;
        S1 vr3 = default(S1);
        M80(vr3);
    }

    public static void M80(S1 arg0)
    {
        arg0.F2 += (ushort)(arg0.F1 % (uint)arg0.M82(ref s_28));
        System.Console.WriteLine(arg0.F2);
    }
}

Author:	jakobbotsch
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[jakobbotsch]

The mod transform reorders the read of arg0.F1 and the function call arg0.M82(...):

fgMorphTree (before 17):
               [000024] --CXG------                         ▌  UMOD      int   
               [000011] -----------                         ├──▌  LCL_FLD   int    V00 arg0         [+0]
               [000023] --CXG------                         └──▌  CAST      int <- uint <- long
               [000015] --CXG------                            └──▌  CALL      long   S1.M82
               [000013] ----------- this                          ├──▌  LCL_VAR_ADDR byref  V00 arg0         
               [000014] H---------- arg1                          └──▌  CNS_INT(h) long   0x1bdae801f10 static Fseq[s_28]

...

fgMorphTree (after 17):
               [000047] -ACXG+-----                         ▌  COMMA     int   
               [000041] -ACXG+-----                         ├──▌  ASG       int   
               [000040] D----+-N---                         │  ├──▌  LCL_VAR   int    V05 tmp4         
               [000023] --CXG+-----                         │  └──▌  CAST      int <- uint <- long
               [000015] --CXG+-----                         │     └──▌  CALL      long   S1.M82
               [000013] -----+----- this in x0              │        ├──▌  LCL_VAR   byref  V00 arg0         
               [000014] H----+----- arg1 in x1              │        └──▌  CNS_INT(h) long   0x1bdae801f10 static Fseq[s_28]
               [000046] ---XG+-----                         └──▌  SUB       int   
               [000048] n---G+-----                            ├──▌  IND       int   
               [000011] -----+-----                            │  └──▌  LCL_VAR   byref  V00 arg0         
               [000045] ---XG+-----                            └──▌  MUL       int   
               [000024] ---XG+-----                               ├──▌  UDIV      int   
               [000049] n---G+-----                               │  ├──▌  IND       int   
               [000043] -----+-----                               │  │  └──▌  LCL_VAR   byref  V00 arg0         
               [000044] -----+-----                               │  └──▌  LCL_VAR   int    V05 tmp4         
               [000042] -----+-----                               └──▌  LCL_VAR   int    V05 tmp4         

This is probably exposed by recent local morph changes causing us to forward sub the access of arg0.F1.