re PR target/20126 (Inlined memcmp makes one argument null on entry)

re PR target/20126 (Inlined memcmp makes one argument null on entry)

gcc/ChangeLog:
PR target/20126
* loop.c (loop_givs_rescan): If replacement of DEST_ADDR failed,
set the original address pseudo to the correct value before the
original insn, if possible, and leave the insn alone, otherwise
create a new pseudo, set it and replace it in the insn.
* recog.c (validate_change_maybe_volatile): New.
* recog.h (validate_change_maybe_volatile): Declare.
gcc/testsuite/ChangeLog:
* gcc.dg/pr20126.c: New.

From-SVN: r97939