JIT: Assertion failed '!"Write to unaliased local overlaps outstanding read"' during 'Rationalize IR'

[jakobbotsch]

// Generated by Fuzzlyn v1.5 on 2022-11-02 10:14:49
// Run on X64 Windows
// Seed: 14352496230403376157
// Reduced from 191.3 KiB to 0.5 KiB in 00:01:55
// Hits JIT assert in Release:
// Assertion failed '!"Write to unaliased local overlaps outstanding read"' in 'Program:Main(Fuzzlyn.ExecutionServer.IRuntime)' during 'Rationalize IR' (IL size 42; hash 0xade6b36b; FullOpts)
//
//     File: C:\dev\dotnet\runtime3\src\coreclr\jit\lir.cpp Line: 1407
//
public struct S0
{
    public int F1;
}

public struct S2
{
    public uint F0;
    public ushort F1;
}

public class Program
{
    public static S2 s_1;
    public static S2 s_16;
    public static sbyte[][] s_20;
    public static int[] s_21;
    public static void Main()
    {
        var vr9 = new S0();
        s_1.F0 <<= M41(vr9, ref s_16.F1);
    }

    public static sbyte M41(S0 argThis, ref ushort arg1)
    {
        argThis.F1 = s_21[0];
        return s_20[0][0];
    }
}

Full output:

                      [000083] -----------                            IL_OFFSET void   INLRT @ 0x000[E-]
       N001 (  1,  1) [000047] -----------                   t47 =    CNS_INT   int    0 $80
                                                                   ┌──▌  t47    int
       N003 (  5,  4) [000048] DA---------                         ▌  STORE_LCL_VAR int    V04 tmp3         d:2
                      [000084] -----------                            IL_OFFSET void   INLRT @ 0x008[E-]
       N001 (  2, 10) [000009] -----------                    t9 =    CNS_INT   long   0x7ff9a30af770 $100
       N002 (  1,  1) [000010] -----------                   t10 =    CNS_INT   int    3 $82
                                                                   ┌──▌  t9     long   arg0 in rcx
                                                                   ├──▌  t10    int    arg1 in rdx
       N003 ( 17, 18) [000011] H-CXG------                   t11 = ▌  CALL help long   HELPER.CORINFO_HELP_GETSHARED_NONGCSTATIC_BASE $1c1
                                                                   ┌──▌  t11    long
       N005 ( 17, 18) [000077] DA-XG------                         ▌  STORE_LCL_VAR long   V08 cse0         d:1
       N008 (  3, 10) [000004] I----------                    t4 =    CNS_INT(h) long   0x1432dc01ec0 static box ptr $200
                                                                   ┌──▌  t4     long
       N009 (  5, 12) [000005] #----------                    t5 = ▌  IND       ref    $240
       N010 (  1,  1) [000006] -----------                    t6 =    CNS_INT   long   8 Fseq[s_1] $102
                                                                   ┌──▌  t5     ref
                                                                   ├──▌  t6     long
       N011 (  7, 14) [000007] -----------                    t7 = ▌  ADD       byref  $280
                                                                   ┌──▌  t7     byref
       N014 ( 25, 33) [000050] DA-XG------                         ▌  STORE_LCL_VAR byref  V05 tmp4         d:2
       N015 (  1,  1) [000051] -----------                   t51 =    LCL_VAR   byref  V05 tmp4         u:2 $280
                                                                   ┌──▌  t51    byref
       N016 (  2,  2) [000052] -----O-----                         ▌  NULLCHECK byte   $VN.Void
       N001 (  1,  1) [000018] -----------                   t18 =    LCL_VAR   byref  V05 tmp4         u:2 $280
                                                                   ┌──▌  t18    byref
       N002 (  3,  2) [000019] n---GO-----                   t19 = ▌  IND       int    <l:$340, c:$380>
                                                                   ┌──▌  t19    int
       N004 (  3,  3) [000036] DA--GO-----                         ▌  STORE_LCL_VAR int    V03 tmp2         d:2
read:  N001 (  1,  1) [000017] -----------                   t17 =    LCL_VAR   byref  V05 tmp4         u:2 (last use) $280
       N003 (  1,  1) [000081] -----------                   t81 =    CNS_INT   int    0 $80
                                                                   ┌──▌  t81    int
       N005 (  1,  3) [000073] DA---------                         ▌  STORE_LCL_VAR int    V07 tmp6         d:2
       N006 (  3, 10) [000021] I----------                   t21 =    CNS_INT(h) long   0x1432dc01ec8 static box ptr $204
                                                                   ┌──▌  t21    long
       N007 (  5, 12) [000022] #----------                   t22 = ▌  IND       ref    $241
       N008 (  1,  1) [000023] -----------                   t23 =    CNS_INT   long   8 Fseq[s_16] $102
                                                                   ┌──▌  t22    ref
                                                                   ├──▌  t23    long
       N009 (  7, 14) [000024] -----------                   t24 = ▌  ADD       byref  $281
                                                                   ┌──▌  t24    byref
write: N011 (  7, 14) [000059] DA--G------                         ▌  STORE_LCL_VAR byref  V05 tmp4         d:3
       N012 (  1,  1) [000063] -----------                   t63 =    LCL_VAR   byref  V05 tmp4         u:3 (last use) $281
       N013 (  1,  1) [000064] -----------                   t64 =    CNS_INT   long   4 $105
                                                                   ┌──▌  t63    byref
                                                                   ├──▌  t64    long
       N014 (  3,  3) [000065] -----------                   t65 = ▌  ADD       byref  $282
                                                                   ┌──▌  t65    byref
       N017 ( 10, 17) [000070] DA--GO-----                         ▌  STORE_LCL_VAR byref  V06 tmp5         d:2
       N018 (  1,  1) [000071] -----------                   t71 =    LCL_VAR   byref  V06 tmp5         u:2 (last use) $282
       N019 (  1,  1) [000082] -----------                   t82 =    CNS_INT   int    0 $80
                                                                   ┌──▌  t71    byref  arg1 in rdx
                                                                   ├──▌  t82    int    arg0 in rcx
       N020 ( 33, 29) [000032] --CXGO-----                   t32 = ▌  CALL      int    Program.M41 $381
       N021 (  1,  1) [000039] -----------                   t39 =    CNS_INT   int    31 $83
                                                                   ┌──▌  t32    int
                                                                   ├──▌  t39    int
       N022 ( 35, 31) [000040] ---XGO-----                   t40 = ▌  AND       int    $341
       N023 (  1,  1) [000037] -----------                   t37 =    LCL_VAR   int    V03 tmp2         u:2 (last use) <l:$340, c:$380>
                                                                   ┌──▌  t37    int
                                                                   ├──▌  t40    int
       N024 ( 40, 33) [000041] ---XGO-----                   t41 = ▌  LSH       int    <l:$342, c:$343>
                                                                   ┌──▌  t17    byref
                                                                   ├──▌  t41    int
user:                 [000085] -ACXGO-----                         ▌  STOREIND  int
                      [000086] -----------                            IL_OFFSET void   INLRT @ 0x029[E-]
       N001 (  0,  0) [000044] -----------                            RETURN    void   $VN.Void

Assert failure(PID 33568 [0x00008320], Thread: 26964 [0x6954]): Assertion failed '!"Write to unaliased local overlaps outstanding read"' in 'Program:Main()' during 'Rationalize IR' (IL size 42; hash 0xcb019401; FullOpts)

    File: C:\dev\dotnet\runtime3\src\coreclr\jit\lir.cpp Line: 1407
    Image: C:\dev\dotnet\runtime3\artifacts\tests\coreclr\windows.x64.Checked\Tests\Core_Root\corerun.exe

Looks introduced/exposed by #77641, cc @SingleAccretion

[ghost]

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Issue Details

---

// Generated by Fuzzlyn v1.5 on 2022-11-02 10:14:49
// Run on X64 Windows
// Seed: 14352496230403376157
// Reduced from 191.3 KiB to 0.5 KiB in 00:01:55
// Hits JIT assert in Release:
// Assertion failed '!"Write to unaliased local overlaps outstanding read"' in 'Program:Main(Fuzzlyn.ExecutionServer.IRuntime)' during 'Rationalize IR' (IL size 42; hash 0xade6b36b; FullOpts)
//
//     File: C:\dev\dotnet\runtime3\src\coreclr\jit\lir.cpp Line: 1407
//
public struct S0
{
    public int F1;
}

public struct S2
{
    public uint F0;
    public ushort F1;
}

public class Program
{
    public static S2 s_1;
    public static S2 s_16;
    public static sbyte[][] s_20;
    public static int[] s_21;
    public static void Main()
    {
        var vr9 = new S0();
        s_1.F0 <<= M41(vr9, ref s_16.F1);
    }

    public static sbyte M41(S0 argThis, ref ushort arg1)
    {
        argThis.F1 = s_21[0];
        return s_20[0][0];
    }
}

Looks introduced/exposed by #77641, cc @SingleAccretion

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

[SingleAccretion]

This is a tricky issue. Distilled, we have (local) copy propagation replacing a use of a local that will redefined before being used by the parent, i. e.

USER
  op1: LCL_VAR V02 => V05
  op2: ...
       STORE_LCL_VAR<V05>(...)

(The V05 local is a "big offset morphing" temp)

This is a fundamental limitation that we are running into here, the only way to solve it is through some workaround...