[Bug target/19922] xor is enclosed in loop, and exectuted on each iteration of for statement

["uros at kss-loka dot si" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #6 from uros at kss-loka dot si  2005-10-28 06:05 -------
(In reply to comment #5)
> The realy problem here is that the xor is produced after reload and is really
> only done on some x86 targets.
> 
This happens in following peephole2 pattern:

;; Don't move an immediate directly to memory when the instruction
;; gets too big.
(define_peephole2
  [(match_scratch:SI 1 "r")
   (set (match_operand:SI 0 "memory_operand" "")
        (const_int 0))]
  "! optimize_size
   && ! TARGET_USE_MOV0
   && TARGET_SPLIT_LONG_MOVES
   && get_attr_length (insn) >= ix86_cost->large_insn
   && peep2_regno_dead_p (0, FLAGS_REG)"
  [(parallel [(set (match_dup 1) (const_int 0))
              (clobber (reg:CC FLAGS_REG))])
   (set (match_dup 0) (match_dup 1))]
  "")

The problem is, that peephole2 optimizations happens very late, and no further
RTL pass can eliminate redundant loads.

Do we need a post-peephole2 gcse pass? :)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19922