[llvm-dev] 'Simple Register Coalescing' pass error

[Quentin Colombet via llvm-dev]

Hi Josh,

That sounds like a bug, but I don’t have enough information to know what is going on.

Could you file a public report in buzgilla and attach the IR (run clang with `-emit-llvm`) and the debug output of the coalescer (-mllvm -debug-only=regalloc)?

Thanks,
-Quentin

> On Apr 11, 2019, at 9:32 PM, Josh Sharp via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
>  
> Hi all,
> I have an error I do not understand. My program crashes during the 'Simple Register Coalescing' pass. All I know is that the crash happens inside LiveRange::Query() in llvm/include/llvm/CodeGen/LiveInterval.h and is due to the fact that EarlyVal is null and causes a crash when evaluating if (EarlyVal->def == Idx.getBaseIndex()). What could be the reason why EarlyVal is null? The function on which the pass is being run is:
> 
> 
> 
> void foo(uint8_t* input, const uint8_t* key, uint8_t *output, size_t len)
> {
> 
> uint16_t np1 = (len * 8)/64;
> uint16_t n = np1 - 1;
> uint64_t A;
> uint64_t R[n+1];
> int i,j;
> 
> 
>        memcpy(&A,input,8);
>        for (i = 1; i<= n;i++)
>        {
>            memcpy(&R[i], input + 8*i,8);
>        }
> 
> 
>        for (j = 5; j >= 0; j--)
>            for (i = n; i >= 1; i--)
>            {
>             uint64_t l_input[2] =
>             {
>               A ^ (((uint64_t)(n*j+i))<<56),
>               R[i]
>             };
> 
>                dec((uint8_t*)l_input, key, output);
>                memcpy(&A,output,8);
>                memcpy(&R[i],output+8,8);
>            }
> 
>        memcpy(output,&A,8);
>        int k;
>        for(k=1;k<(n+1);k++)
>        {
>         memcpy(output+8*k,&R[k],8);
>        }
> }
> 
> Thanks.
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