[Bug rtl-optimization/49088] New: Combine fails to properly handle zero-extension and signed int constant

["hjl.tools at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49088

           Summary: Combine fails to properly handle zero-extension and
                    signed int constant
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: hjl.tools@gmail.com
                CC: ebotcazou@gcc.gnu.org


We have

(insn 5 2 7 2 (parallel [
            (set (reg/f:DI 61)
                (plus:DI (reg/f:DI 20 frame)
                    (const_int -64 [0xffffffffffffffc0])))
            (clobber (reg:CC 17 flags))
        ]) x.i:12 252 {*adddi_1}
     (expr_list:REG_UNUSED (reg:CC 17 flags)
        (nil)))
(insn 17 9 18 2 (parallel [
            (set (reg:SI 72)
                (plus:SI (subreg:SI (reg/f:DI 61) 0)
                    (const_int 6 [0x6])))
            (clobber (reg:CC 17 flags))
        ]) x.i:14 251 {*addsi_1}
     (expr_list:REG_DEAD (reg/f:DI 61)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

(insn 18 17 10 2 (set (reg:DI 73)
        (zero_extend:DI (reg:SI 72))) x.i:14 112 {*zero_extendsidi2_rex64}
     (expr_list:REG_DEAD (reg:SI 72)
        (nil)))

(insn 11 10 12 2 (set (reg:DI 68)
        (reg:DI 73)) x.i:14 62 {*movdi_internal_rex64}
     (expr_list:REG_DEAD (reg:DI 73)
        (nil)))

combine turns it into

(insn 18 17 10 2 (set (reg:DI 73) 
        (const_int 4294967238 [0xffffffc6])) x.i:14 62 {*movdi_internal_rex64}
     (nil))

(insn 11 10 12 2 (set (reg:DI 68)
        (plus:DI (reg/f:DI 20 frame)
            (reg:DI 73))) x.i:14 247 {*lea_1}
     (expr_list:REG_DEAD (reg:DI 73)
        (nil)))

"const_int -64" is signed, not unsigned.