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Date: Tue, 18 Oct 2005 00:10:00 -0000
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References: <bug-24418-11457@http.gcc.gnu.org/bugzilla/>
Subject: [Bug rtl-optimization/24418] Redudant compare to zero not eliminated
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From: "pinskia at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
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------- Comment #3 from pinskia at gcc dot gnu dot org  2005-10-18 00:09 -------
and yes eax/reg 68 (or n) is dead after the compare in combine:
(insn 37 36 39 3 (parallel [
            (set (reg/v:SI 68 [ n ])
                (minus:SI (reg:SI 71)
                    (reg/v:SI 66 [ med ])))
            (clobber (reg:CC 17 flags))
        ]) 172 {*subsi_1} (insn_list:REG_DEP_TRUE 36 (nil))
    (expr_list:REG_DEAD (reg:SI 71)
        (expr_list:REG_UNUSED (reg:CC 17 flags)
            (nil))))

(insn 39 37 40 3 (set (reg:CC 17 flags)
        (compare:CC (reg/v:SI 68 [ n ])
            (const_int 0 [0x0]))) 2 {*cmpsi_1_insn} (insn_list:REG_DEP_TRUE 37
(nil))
    (expr_list:REG_DEAD (reg/v:SI 68 [ n ])
        (nil)))


Note the REG_DEAD, so what RTH said is wrong.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24418