Introduce peephole2 pattern to convert from:

   mov %esi, %edx
   negl %eax
   adcl $0, %edx
   negl %edx
 to:
   xorl %edx, %edx
   negl %eax
   sbbl %esi, %edx

This conversion is profitable only when initial move is found.  Otherwise,
additional move to a temporary together with clearing xor is needed.

2022-04-29  Uroš Bizjak  <ubizjak@gmail.com>

gcc/ChangeLog:

    PR target/51954
    * config/i386/i386.md (adcl/neg -> sbb peephole): New peephole2.
gcc/testsuite/ChangeLog:

    PR target/51954
    * gcc.target/i386/pr51954.c: New test.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Pushed to master.

Uros.