[PATCH] D71833: [PowerPC] Fix some bugs of the rlwinm folding

[qshanz via Phabricator via llvm-commits]

steven.zhang added a comment.

In D71833#1794987 <https://reviews.llvm.org/D71833#1794987>, @shchenz wrote:

> Thanks for finding the bug in the testcases. I have modified them in NFC patch https://reviews.llvm.org/rG79b3325be0b016fdc1a2c55bce65ec9f1e5f4eb6
>
> Could you please help to be more specific about the invalid case in the description?
>
> Below c code gives a **valid** result:
>
>   #include <stdio.h>
>  
>   #define rlwinm( output, input, sh, mb, me ) \
>      __asm__( "rlwinm %0, %1, %2, %3, %4" \
>             : "=r"(output) \
>             : "r"(input), "i"(sh), "i"(mb), "i"(me) \
>             : )
>  
>   int main()
>   {
>      unsigned long y,z,t ;
>  
>      int i = 0;
>  
>      for (unsigned x = 0; x < 4294967295; x++)  {
>        rlwinm( y, x, 27, 30, 10) ;
>        rlwinm( z, y, 19, 0, 12);
>        rlwinm(t, x, 14, 11, 12);
>        if (z != t) {
>          printf("0x%016lX -> 0x%016lX, 0x%016lX\n", x, y, z);
>          printf("0x%016lX -> 0x%016lX\n", x, t);
>          i = 100;
>          break;
>       }
>      }
>      if (i == 0)
>        printf("valid\n");
>      else
>        printf("invalid\n");
>      return 0;
>   }
>
>
> So I guess
>
>   %2:gprc = RLWINM %1:gprc, 27, 30, 10
>   %3:gprc = RLWINM %2:gprc, 19, 0, 12
>
>
> should always be equal to
>
>   %3:gprc = RLWINM %1, 14, 11, 12
>
>
> for type i32 and i64 also?


This is the bad transformation:

  %1:g8rc = RLWINM8 %0:g8rc, 0, 16, 9
  %2:g8rc = RLWINM8 killed %1:g8rc, 0, 0, 31

->

  %2:g8rc = RLWINM8 %0:g8rc, 0, 16, 9


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71833/new/

https://reviews.llvm.org/D71833