[Bug rtl-optimization/52838] [x32] missed optimization for pointer return value

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52838

Uros Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-04-04
                 CC|                            |ebotcazou at gcc dot
                   |                            |gnu.org
          Component|target                      |rtl-optimization
     Ever Confirmed|0                           |1

--- Comment #1 from Uros Bizjak <ubizjak at gmail dot com> 2012-04-04 19:06:57 UTC ---
This looks like a combine problem:

(insn 8 6 9 2 (set (reg/f:SI 59 [ D.1705 ])
        (subreg/s/u:SI (reg:DI 60) 0)) pr52838.c:6 64 {*movsi_internal}
     (expr_list:REG_DEAD (reg:DI 60)
        (nil)))

(insn 9 8 10 2 (set (reg/f:DI 62 [ D.1705 ])
        (zero_extend:DI (reg/f:SI 59 [ D.1705 ]))) pr52838.c:6 112
{*zero_extendsidi2_rex64}
     (expr_list:REG_DEAD (reg/f:SI 59 [ D.1705 ])
        (nil)))

This gets transformed by combine pass:


Trying 8 -> 9:
Successfully matched this instruction:
(set (reg/f:DI 62 [ D.1705 ])
    (reg:DI 60))
deferring deletion of insn with uid = 8.
modifying insn i3     9 r62:DI=r60:DI
      REG_DEAD: r60:DI

into:

(note 8 6 9 2 NOTE_INSN_DELETED)

(insn 9 8 10 2 (set (reg/f:DI 62 [ D.1705 ])
        (reg:DI 60)) pr52838.c:6 62 {*movdi_internal_rex64}
     (expr_list:REG_DEAD (reg:DI 60)
        (nil)))

But, but ... high 32 bits are not cleared anymore!

Confirmed as a rtl optimization issue, adding CCs for their opinion.