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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/51017] [4.8/4.9/5 Regression] GCC performance regression (vs. 4.4/4.5), PRE increases register pressure too much Date: Wed, 18 Feb 2015 11:09:00 -0000 [thread overview] Message-ID: <bug-51017-4-rnhfTbRA1t@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-51017-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51017 --- Comment #21 from Richard Biener <rguenth at gcc dot gnu.org> --- We do already inhibit creating loop-carried dependencies of some kind, but only when vectorization is enabled (because it can inhibit vectorization). But we still PRE invariant loads: Replaced MEM[(vtype * {ref-all})&DES_bs_all + 20528B] with prephitmp_2898 in all uses of _1195 = MEM[(vtype * {ref-all})&DES_bs_all + 20528B] because we know it's {0, 0} on entry. Note that store motion doesn't apply here because those stores are said to alias with the MEM[(vtype * {ref-all})k_2 + 848B] kinds (iterating DES_bs_all.KS.v - unfortunately field-sensitive points-to analysis doesn't help here as the points-to result itself isn't field-sensitive). Of course without store-motion applying this kind of PRE is not really useful. If store-motion applied it would create the same kind of problem, of course (in this case up to 0x300(?) live registers). One possible solution is to simply avoid this kind of "partly" store-motion, that is converting for (;;) reg = MEM; MEM = fn(reg); to reg = MEM; for (;;) reg = fn(reg); MEM = reg; of course this is also a profitable transform. Thus the solution might be instead to limit register pressure in some way by somehow assessing costs to individual transforms. At least it seems to be too difficult for the register allocator to re-materialize 'reg' from MEM (as it would also need to perform sophisticated analysis to determine that, basically undoing the PRE transform).
next prev parent reply other threads:[~2015-02-18 11:09 UTC|newest] Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top 2011-11-08 0:43 [Bug middle-end/51017] New: GCC 4.6 performance regression (vs. 4.4/4.5) solar-gcc at openwall dot com 2011-11-08 0:57 ` [Bug middle-end/51017] " solar-gcc at openwall dot com 2011-11-08 1:05 ` solar-gcc at openwall dot com 2011-12-15 0:34 ` pinskia at gcc dot gnu.org 2012-01-03 4:46 ` solar-gcc at openwall dot com 2012-01-04 19:39 ` solar-gcc at openwall dot com 2012-01-04 22:43 ` jakub at gcc dot gnu.org 2012-01-04 23:00 ` solar-gcc at openwall dot com 2015-02-09 0:12 ` pinskia at gcc dot gnu.org 2015-02-16 0:08 ` solar-gcc at openwall dot com 2015-02-16 1:10 ` solar-gcc at openwall dot com 2015-02-16 10:51 ` [Bug tree-optimization/51017] GCC 4.6 performance regression (vs. 4.4/4.5), PRE increases register pressure rguenth at gcc dot gnu.org 2015-02-17 2:21 ` solar-gcc at openwall dot com 2015-02-17 2:56 ` solar-gcc at openwall dot com 2015-02-17 3:11 ` solar-gcc at openwall dot com 2015-02-17 9:25 ` rguenth at gcc dot gnu.org 2015-02-17 9:27 ` rguenth at gcc dot gnu.org 2015-02-18 0:03 ` solar-gcc at openwall dot com 2015-02-18 1:25 ` solar-gcc at openwall dot com 2015-02-18 3:20 ` solar-gcc at openwall dot com 2015-02-18 10:32 ` [Bug tree-optimization/51017] [4.8/4.9/5 Regression] GCC performance regression (vs. 4.4/4.5), PRE increases register pressure too much rguenth at gcc dot gnu.org 2015-02-18 11:09 ` rguenth at gcc dot gnu.org [this message] 2015-02-25 14:26 ` law at redhat dot com 2015-06-23 8:14 ` [Bug tree-optimization/51017] [4.8/4.9/5/6 " rguenth at gcc dot gnu.org 2015-06-26 20:04 ` [Bug tree-optimization/51017] [4.9/5/6 " jakub at gcc dot gnu.org 2015-06-26 20:33 ` jakub at gcc dot gnu.org 2021-05-14 9:46 ` [Bug tree-optimization/51017] [9/10/11/12 Regression] GCC performance regression (vs. 4.4/4.5), PRE/LIM increase " jakub at gcc dot gnu.org 2021-06-01 8:05 ` rguenth at gcc dot gnu.org 2022-05-27 9:34 ` [Bug tree-optimization/51017] [10/11/12/13 " rguenth at gcc dot gnu.org 2022-06-28 10:30 ` jakub at gcc dot gnu.org 2023-07-07 10:29 ` [Bug tree-optimization/51017] [11/12/13/14 " rguenth at gcc dot gnu.org
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