fwprop not propagating

[Paulo J. Matos]

Hi,

While debugging an issue related to my movmem rule, I noticed that 
fwprop seems to be doing some really strange.

The problem occurs when setting the argument to the block copy 
instruction. The full C code is:
int **
t25 (int *d, int **s)
{
   memcpy (d, *s, 16);
   return s;
}

Before fwprop I have the following chain:
(insn 7 4 8 2 (parallel [
             (set (reg/f:QI 24 [ *s_1(D) ])
                 (mem/f:QI (reg/v/f:QI 23 [ s ]) [2 *s_1(D)+0 S1 A16]))
             (clobber (reg:CC 13 CC))
         ]) memcpy.i:4 6 {*movqi}
      (nil))

(insn 8 7 9 2 (parallel [
             (set (reg:QI 25)
                 (const_int 16 [0x10]))
             (clobber (reg:CC 13 CC))
         ]) memcpy.i:4 6 {*movqi}
      (nil))

(insn 9 8 10 2 (parallel [
             (set (reg/f:QI 26 [ d ])
                 (reg/v/f:QI 22 [ d ]))
             (clobber (reg:CC 13 CC))
         ]) memcpy.i:4 6 {*movqi}
      (nil))

(insn 10 9 11 2 (parallel [
             (set (reg/f:QI 27 [ *s_1(D) ])
                 (reg/f:QI 24 [ *s_1(D) ]))
             (clobber (reg:CC 13 CC))
         ]) memcpy.i:4 6 {*movqi}
      (nil))

(insn 11 10 12 2 (parallel [
             (set (reg:QI 25)
                 (const_int 0 [0]))
             (set (mem:BLK (reg/v/f:QI 22 [ d ]) [0 A16])
                 (mem:BLK (reg/f:QI 24 [ *s_1(D) ]) [0 A16]))
             (set (reg/f:QI 26 [ d ])
                 (plus:QI (reg/v/f:QI 22 [ d ])
                     (reg:QI 25)))
             (set (reg/f:QI 27 [ *s_1(D) ])
                 (plus:QI (reg/f:QI 24 [ *s_1(D) ])
                     (reg:QI 25)))
         ]) memcpy.i:4 21 {bc2}
      (nil))


After fwprop I have:
(insn 2 5 3 2 (parallel [
             (set (reg/v/f:QI 22 [ d ])
                 (reg:QI 1 AL [ d ]))
             (clobber (reg:CC 13 CC))
         ]) memcpy.i:3 6 {*movqi}
      (expr_list:REG_DEAD (reg:QI 1 AL [ d ])
         (expr_list:REG_UNUSED (reg:CC 13 CC)
             (nil))))

(insn 3 2 4 2 (parallel [
             (set (reg/v/f:QI 23 [ s ])
                 (reg:QI 0 AH [ s ]))
             (clobber (reg:CC 13 CC))
         ]) memcpy.i:3 6 {*movqi}
      (expr_list:REG_DEAD (reg:QI 0 AH [ s ])
         (expr_list:REG_UNUSED (reg:CC 13 CC)
             (nil))))

(note 4 3 7 2 NOTE_INSN_FUNCTION_BEG)

(insn 7 4 8 2 (parallel [
             (set (reg/f:QI 24 [ *s_1(D) ])
                 (mem/f:QI (reg/v/f:QI 23 [ s ]) [2 *s_1(D)+0 S1 A16]))
             (clobber (reg:CC 13 CC))
         ]) memcpy.i:4 6 {*movqi}
      (expr_list:REG_UNUSED (reg:CC 13 CC)
         (nil)))

(insn 8 7 11 2 (parallel [
             (set (reg:QI 25)
                 (const_int 16 [0x10]))
             (clobber (reg:CC 13 CC))
         ]) memcpy.i:4 6 {*movqi}
      (expr_list:REG_UNUSED (reg:CC 13 CC)
         (nil)))

(insn 11 8 16 2 (parallel [
             (set (reg:QI 25)
                 (const_int 0 [0]))
             (set (mem:BLK (reg/v/f:QI 22 [ d ]) [0 A16])
                 (mem:BLK (reg/f:QI 24 [ *s_1(D) ]) [0 A16]))
             (set (reg/f:QI 26 [ d ])
                 (plus:QI (reg/v/f:QI 22 [ d ])
                     (reg:QI 25)))
             (set (reg/f:QI 27 [ *s_1(D) ])
                 (plus:QI (reg/f:QI 24 [ *s_1(D) ])
                     (reg:QI 25)))
         ]) memcpy.i:4 21 {bc2}
      (expr_list:REG_DEAD (reg/f:QI 24 [ *s_1(D) ])
         (expr_list:REG_DEAD (reg/v/f:QI 22 [ d ])
             (expr_list:REG_UNUSED (reg/f:QI 27 [ *s_1(D) ])
                 (expr_list:REG_UNUSED (reg/f:QI 26 [ d ])
                     (expr_list:REG_UNUSED (reg:QI 25)
                         (nil)))))))


I understand that fwprop can delete insn 9 and 10, but shouldn't it then 
update insn 11 so that references to reg:QI 26 and reg:QI 27 now 
reference reg:QI 22 and reg:QI 24 respectively?

Cheers,
-- 
PMatos