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

[ChenZheng via Phabricator via llvm-commits]

shchenz added a comment.

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?



================
Comment at: llvm/lib/Target/PowerPC/PPCMIPeephole.cpp:904
           if (MI.getOpcode() == PPC::RLWINM || MI.getOpcode() == PPC::RLWINM8) {
+            if (MRI->hasOneNonDBGUse(FoldingReg)) {
+              ToErase = SrcMI;
----------------
We can delete the SrcMI only if it is not a record form?


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  https://reviews.llvm.org/D71833/new/

https://reviews.llvm.org/D71833