mov arguments are still the same

["Paulo J. Matos" <pocmatos@gmail.com>]

Hi,

I have touched this subject before:
http://thread.gmane.org/gmane.comp.gcc.devel/116198/focus=116200

Now, at the time I didn't pursue this issue but now with 4.4.4 this 
keeps happening and I traced it to the cprop_hardreg replacing a 
register which makes the set insn having the same source and dest.

Here's insn 32 from pass 183:ce3

(insn 32 31 33 4 h.c:51 (set (reg:QI 1 AL)
         (reg/f:QI 8 @H'fff9 [33])) 4 {*movqi} (expr_list:REG_DEAD 
(reg/f:QI 8 @H'fff9 [33])
         (expr_list:REG_EQUAL (plus:QI (reg/f:QI 6 Y)
                 (const_int 1 [0x1]))
             (nil))))


Now the same insn after the following pass 185:cprop_hardreg


insn 32: replaced reg 8 with 1

...

(insn 32 31 33 4 h.c:51 (set (reg:QI 1 AL)
         (reg/f:QI 1 AL [33])) 4 {*movqi} (expr_list:REG_DEAD (reg/f:QI 
8 @H'fff9 [33])
         (expr_list:REG_EQUAL (plus:QI (reg/f:QI 6 Y)
                 (const_int 1 [0x1]))
             (nil))))


This stays as is until assembler generation, which is really annoying 
cause it generates an instruction (which is basically a nop) like:
...
mov AL,AL
...

Is this a known issue? I can't see how this is a problem with my backend 
but might as well be. Maybe cprop_regmove should check if it is making 
the src equal to dest and if it is remove the insn?

Any suggestions?

--
PMatos