Eliminate redundant compare between set{z,nz} and j{z,nz}:
setz %al; test %al,%al; jz <...> -> setz %al; jnz <...> and
setnz %al, test %al,%al; jz <...> -> setnz %al; jz <...>.

We can use the original Zero-flag value instead of setting the
temporary register and testing it for zero.

gcc/ChangeLog:

    * config/i386/i386.md (redundant compare peephole2):
    New peephole2 pattern.

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

Also tested by building and booting the linux kernel (where the
peephole2 triggers several times).

I was not able to craft the testcase, the original sequence is very
elusive and requires reuse of the value, set from the flags elsewhere
in the function in a very specific way.

Uros.