[Bug middle-end/28970] [4.1 Regression] Wrong code for simple loop test case

[rguenth at gcc dot gnu dot org]

------- Comment #3 from rguenth at gcc dot gnu dot org  2006-10-16 12:07 -------
This is a bug in loop.c

<bb 0>:
  pretmp.61 = q - 1;
  outgo = 0;

<L0>:;
  outgo.62 = outgo + 1;
  outgo = MIN_EXPR <pretmp.61, outgo.62>;
  j = tar (outgo * bcount);
  if (j != -1) goto <L0>; else goto <L4>;

<L4>:;
  return;

Bug in biv selection, so strength reduction messes up:

Loop from 45 to 46: 12 real insns.
Biv 60: insn 19 const (reg 59 [ pretmp.26 ])
Biv 60: insn 22 const (1)
Biv 60: verified
Biv 60: initialized at insn 13: initial value (0)
Giv 58: insn 17 src reg 60 benefit 4 lifetime 6

60 is not a Biv:

(insn 19 17 20 1 (set (reg/v:SI 60 [ outgo ])
        (reg:SI 59 [ pretmp.26 ])) 40 {*movsi_1} (nil)
    (nil))

(insn 20 19 21 1 (set (reg:CCGC 17 flags)
        (compare:CCGC (reg/v:SI 60 [ outgo ])
            (reg/v:SI 58 [ outgo.27 ]))) 5 {*cmpsi_1_insn} (nil)
    (nil))

(jump_insn 21 20 41 1 (set (pc)
        (if_then_else (le (reg:CCGC 17 flags)
                (const_int 0 [0x0]))
            (label_ref 23)
            (pc))) 531 {*jcc_1} (nil)
    (expr_list:REG_BR_PROB (const_int 5000 [0x1388])
        (nil)))
;; End of basic block 1, registers live:
 (nil)

;; Start of basic block 2, registers live: (nil)
(note 41 21 22 2 [bb 2] NOTE_INSN_BASIC_BLOCK)

(insn 22 41 23 2 (set (reg/v:SI 60 [ outgo ])
        (reg/v:SI 58 [ outgo.27 ])) 40 {*movsi_1} (nil)
    (nil))
;; End of basic block 2, registers live:
 (nil)

;; Start of basic block 3, registers live: (nil)
(code_label 23 22 42 3 3 "" [1 uses])


now strength reduction does:

(insn 19 17 51 1 (set (reg/v:SI 60 [ outgo ])
        (reg:SI 59 [ pretmp.26 ])) -1 (nil)
    (nil))

(insn 51 19 20 1 (parallel [
            (set (reg:SI 66)
                (mult:SI (reg:SI 59 [ pretmp.26 ])
                    (reg/v:SI 63 [ bcount ])))
            (clobber (reg:CC 17 flags))
        ]) -1 (nil)
    (nil))

(insn 20 51 21 1 (set (reg:CCGC 17 flags)
        (compare:CCGC (reg/v:SI 60 [ outgo ])
            (reg/v:SI 58 [ outgo.27 ]))) -1 (nil)
    (nil))

(jump_insn 21 20 41 1 (set (pc)
        (if_then_else (le (reg:CCGC 17 flags)
                (const_int 0 [0x0]))
            (label_ref 23)
            (pc))) -1 (nil)
    (expr_list:REG_BR_PROB (const_int 5000 [0x1388])
        (nil)))
;; End of basic block 1, registers live:
 (nil)

;; Start of basic block 2, registers live: (nil)
(note 41 21 22 2 [bb 2] NOTE_INSN_BASIC_BLOCK)

(insn 22 41 50 2 (set (reg/v:SI 60 [ outgo ])
        (reg/v:SI 58 [ outgo.27 ])) -1 (nil)
    (nil))

(insn 50 22 23 2 (parallel [
            (set (reg:SI 66)
                (plus:SI (reg:SI 66)
                    (reg/v:SI 63 [ bcount ])))
            (clobber (reg:CC 17 flags))
        ]) -1 (nil)
    (nil))
;; End of basic block 2, registers live:
 (nil)

;; Start of basic block 3, registers live: (nil)
(code_label 23 50 42 3 3 "" [1 uses])


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rakdver at gcc dot gnu dot
                   |                            |org
   Last reconfirmed|2006-09-07 05:01:38         |2006-10-16 12:07:36
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28970