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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/112835] inverting the result of memcmp() produces inefficient code Date: Sun, 03 Dec 2023 20:35:37 +0000 [thread overview] Message-ID: <bug-112835-4-AZlS8aG1vu@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-112835-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112835 Andrew Pinski <pinskia at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|UNCONFIRMED |NEW Last reconfirmed| |2023-12-03 Target| |x86_64-linux-gnu | |aarch64-linux-gnu Component|target |middle-end Keywords| |missed-optimization Ever confirmed|0 |1 --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> --- Confirmed. aarch64 code generation is slightly better: ... .L2: mov w0, 1 eor w0, w0, 1 ret ... mov w0, 0 eor w0, w0, 1 ret But there is no reason for the mov followed by eor there, it should just be a mov. Note the gimple level is fine: _1 = __builtin_memcmp_eq (a_3(D), b_4(D), 12); _5 = _1 == 0; Expansion does: ``` (jump_insn 14 13 33 4 (set (pc) (if_then_else (ne (reg:CC 66 cc) (const_int 0 [0])) (label_ref 19) (pc))) "/app/example.cpp":5:24 -1 (int_list:REG_BR_PROB 708669604 (nil)) -> 19) (note 33 14 15 5 [bb 5] NOTE_INSN_BASIC_BLOCK) (insn 15 33 16 5 (set (reg:SI 92 [ _1 ]) (const_int 0 [0])) "/app/example.cpp":5:24 -1 (nil)) (jump_insn 16 15 17 5 (set (pc) (label_ref 21)) "/app/example.cpp":5:24 -1 (nil) -> 21) (barrier 17 16 18) (barrier 18 17 19) (code_label 19 18 34 6 2 (nil) [2 uses]) (note 34 19 20 6 [bb 6] NOTE_INSN_BASIC_BLOCK) (insn 20 34 21 6 (set (reg:SI 92 [ _1 ]) (const_int 1 [0x1])) "/app/example.cpp":5:24 -1 (nil)) (code_label 21 20 35 7 3 (nil) [1 uses]) (note 35 21 22 7 [bb 7] NOTE_INSN_BASIC_BLOCK) (insn 22 35 23 7 (set (reg:CC 66 cc) (compare:CC (reg:SI 92 [ _1 ]) (const_int 0 [0]))) "/app/example.cpp":5:33 discrim 1 -1 (nil)) (insn 23 22 24 7 (set (reg:SI 102) (eq:SI (reg:CC 66 cc) (const_int 0 [0]))) "/app/example.cpp":5:33 discrim 1 -1 (nil)) ``` Seems like we could do a better job at expansion here ...
prev parent reply other threads:[~2023-12-03 20:35 UTC|newest] Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-12-03 18:09 [Bug tree-optimization/112835] New: " gnu at kosak dot com 2023-12-03 20:35 ` pinskia at gcc dot gnu.org [this message]
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