[Bug rtl-optimization/57046] [4.8/4.9 Regression] wrong code generated by gcc 4.8.0 on i686

["jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57046

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-04-23 12:26:35 UTC ---
We have after the get_value call:
(insn 73 30 32 6 (set (reg:SI 76 [ D.1441 ])
        (reg:SI 0 ax)) pr57046.c:42 85 {*movsi_internal}
     (expr_list:REG_DEAD (reg:SI 0 ax)
        (nil)))
(insn 32 73 33 6 (parallel [
            (set (reg:SI 73 [ D.1443 ])
                (ashift:SI (subreg:SI (reg:DI 60 [ D.1441 ]) 0)
                    (const_int 2 [0x2])))
            (clobber (reg:CC 17 flags))
        ]) 502 {*ashlsi3_1}
     (expr_list:REG_DEAD (reg:DI 60 [ D.1441 ])
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

and IRA decides to put pseudo 76 into %ebx and pseudo 60 into %ecx.  Either it
is an IRA bug, or IRA takes into account that we only really need the low
32-bits of pseudo 60 at that point.  In any case, reload loads SImode %ecx from
the stack and uses it in the shift, while LRA loads full DImode %ecx (i.e. %ecx
and %ebx) from the stack, then uses just the low bits from that (i.e. %ecx) in
the shift.  So the LRA generated code clobbers the value in %ebx, and get_value
call is even later on DCEd because of it.