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From: "olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/53987] [SH] Unnecessary zero-extensions Date: Thu, 15 Jan 2015 01:37:00 -0000 [thread overview] Message-ID: <bug-53987-4-VOsspQQBRp@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-53987-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53987 --- Comment #9 from Oleg Endo <olegendo at gcc dot gnu.org> --- Another related issue is this example function: unsigned char h (unsigned char a, int b) { return (unsigned char)(a + b); } compiling with -O2 -mrenesas (which allows undefined high bits in the return value): extu.b r4,r4 << not needed mov r5,r0 rts add r4,r0 It seems that the fwprop1 pass causes this. The initial RTL for this looks like this: (insn 2 5 3 2 (set (reg/v:SI 165 [ a ]) (zero_extend:SI (reg:QI 4 r4 [ a ]))) sh_tmp.cpp:1550 -1 (nil)) (insn 3 2 4 2 (set (reg/v:SI 166 [ b ]) (reg:SI 5 r5 [ b ])) sh_tmp.cpp:1550 -1 (nil)) (note 4 3 7 2 NOTE_INSN_FUNCTION_BEG) (insn 7 4 8 2 (set (reg:QI 168) (subreg:QI (reg/v:SI 166 [ b ]) 0)) sh_tmp.cpp:1551 -1 (nil)) (insn 8 7 9 2 (set (reg:SI 169) (plus:SI (reg/v:SI 165 [ a ]) (subreg:SI (reg:QI 168) 0))) sh_tmp.cpp:1551 -1 (nil)) (insn 9 8 13 2 (set (reg:QI 164 [ <retval> ]) (subreg:QI (reg:SI 169) 0)) sh_tmp.cpp:1551 -1 (nil)) (insn 13 9 14 2 (set (reg/i:QI 0 r0) (reg:QI 164 [ <retval> ])) sh_tmp.cpp:1552 -1 (nil)) (insn 14 13 0 2 (use (reg/i:QI 0 r0)) sh_tmp.cpp:1552 -1 (nil)) Notice that the plus op is expanded as a subreg:SI (reg:QI) and the result is then taken as a subreg:QI. This should be OK with the addsi3 pattern. However, fwprop1 then propagates the hardregs and eliminates the subregs: (note 5 0 2 2 [bb 2] NOTE_INSN_BASIC_BLOCK) (insn 2 5 3 2 (set (reg/v:SI 165 [ a ]) (zero_extend:SI (reg:QI 4 r4 [ a ]))) sh_tmp.cpp:1550 218 {*zero_extendqisi2_compact} (expr_list:REG_DEAD (reg:QI 4 r4 [ a ]) (nil))) (insn 3 2 4 2 (set (reg/v:SI 166 [ b ]) (reg:SI 5 r5 [ b ])) sh_tmp.cpp:1550 252 {movsi_ie} (expr_list:REG_DEAD (reg:SI 5 r5 [ b ]) (nil))) (note 4 3 8 2 NOTE_INSN_FUNCTION_BEG) (insn 8 4 13 2 (set (reg:SI 169) (plus:SI (reg/v:SI 165 [ a ]) (reg/v:SI 166 [ b ]))) sh_tmp.cpp:1551 63 {*addsi3_compact} (expr_list:REG_DEAD (reg:QI 168 [ b ]) (expr_list:REG_DEAD (reg/v:SI 165 [ a ]) (nil)))) (insn 13 8 14 2 (set (reg/i:QI 0 r0) (subreg:QI (reg:SI 169) 0)) sh_tmp.cpp:1552 270 {*movqi} (expr_list:REG_DEAD (reg:SI 169) (nil))) (insn 14 13 0 2 (use (reg/i:QI 0 r0)) sh_tmp.cpp:1552 -1 (nil)) After that, everything is pretty much set and the zero extension will not be eliminated anymore.
next prev parent reply other threads:[~2015-01-15 1:37 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2012-07-16 23:50 [Bug target/53987] New: [SH] Unnecessary zero-extension before cmp/eq olegendo at gcc dot gnu.org 2012-08-31 18:14 ` [Bug target/53987] " olegendo at gcc dot gnu.org 2013-10-29 21:58 ` olegendo at gcc dot gnu.org 2013-12-16 19:07 ` olegendo at gcc dot gnu.org 2014-12-17 21:09 ` olegendo at gcc dot gnu.org 2014-12-21 16:54 ` [Bug target/53987] [SH] Unnecessary zero-extensions olegendo at gcc dot gnu.org 2014-12-22 22:27 ` olegendo at gcc dot gnu.org 2014-12-25 1:11 ` olegendo at gcc dot gnu.org 2014-12-30 17:26 ` olegendo at gcc dot gnu.org 2015-01-15 1:37 ` olegendo at gcc dot gnu.org [this message] 2015-01-24 13:06 ` olegendo at gcc dot gnu.org 2015-01-27 23:08 ` olegendo at gcc dot gnu.org 2015-08-01 9:57 ` olegendo at gcc dot gnu.org 2015-09-09 12:15 ` olegendo at gcc dot gnu.org
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