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From: "vmakarov at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/65862] [MIPS] IRA/LRA issue: integers spilled to floating-point registers Date: Mon, 27 Apr 2015 16:17:00 -0000 [thread overview] Message-ID: <bug-65862-4-ZgSdu2yMKz@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-65862-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65862 Vladimir Makarov <vmakarov at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |vmakarov at gcc dot gnu.org --- Comment #3 from Vladimir Makarov <vmakarov at gcc dot gnu.org> --- The result of the old patch which makes ALL_REGS available changes the order of coloring and, as a consequence, the result of allocation for r218 and r220 after IRA. That is unfortunate result of heuristics approaches. Before the patch: ... Popping a4(r218,l0) -- assign reg 30 Popping a0(r220,l0) -- spill ... Disposition: ... 4:r218 l0 30 6:r219 l0 16 0:r220 l0 mem After patch: Popping a0(r220,l0) -- assign reg 30 Popping a4(r218,l0) -- (memory is more profitable 184 vs 191) spill! ... Disposition: ... 4:r218 l0 mem 6:r219 l0 16 0:r220 l0 30 The costs of MEM and FP_REGS are the same as for example r218 occurs in 2 insns: 59: r218:SI=r194:SI<=0x1 16: pc={(r218:SI!=0)?L18:pc} The costs are equal if cost of moving general regs to/from fp regs or memory are equal. So it looks ok to me. r218 spilled in IRA is reassigned to a fp reg in *LRA*. It could be changed if we used only preferred class in LRA for this. In this case, r218 stays spilled and we remove one insn (saving the allocated fp reg): sdc1 $f20,64($sp) I am not sure, that the result code is better as we access memory 3 times instead of access to $f20. But I could try to use preferred class in LRA (after checking how it affects x86/x86-64 performance), if such solution is ok for you. But I can not just revert the patch making ALL_REGS available to make coloring heuristic more fotunate for your particular case, as it reopens the old PR for which the patch was created and i have no other solutions for the old PR. Robert, please let me know what do you think.
next prev parent reply other threads:[~2015-04-27 16:17 UTC|newest] Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-04-23 16:04 [Bug rtl-optimization/65862] New: " robert.suchanek at imgtec dot com 2015-04-23 16:09 ` [Bug rtl-optimization/65862] " pinskia at gcc dot gnu.org 2015-04-23 16:54 ` robert.suchanek at imgtec dot com 2015-04-27 16:17 ` vmakarov at gcc dot gnu.org [this message] 2015-04-27 17:13 ` wdijkstr at arm dot com 2015-05-06 16:13 ` robert.suchanek at imgtec dot com 2015-05-06 16:21 ` matthew.fortune at imgtec dot com 2015-05-07 18:55 ` vmakarov at gcc dot gnu.org 2015-05-08 18:29 ` vmakarov at gcc dot gnu.org 2015-05-12 20:38 ` vmakarov at gcc dot gnu.org 2015-05-13 7:53 ` robert.suchanek at imgtec dot com 2015-05-14 14:20 ` wdijkstr at arm dot com 2015-05-14 20:41 ` vmakarov at gcc dot gnu.org
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