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From: "rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/98782] [11/12 Regression] Bad interaction between IPA frequences and IRA resulting in spills due to changes in BB frequencies Date: Mon, 20 Dec 2021 18:06:02 +0000 [thread overview] Message-ID: <bug-98782-4-02J19hNnjd@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-98782-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98782 --- Comment #31 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> --- I don't know how relevant this is to the exchange2 problem yet, but for: --------------------------------------------------------------------- #define PROB 0.95 struct L { int data; L *next; L *inner; }; template<int N> struct S { static __attribute__((always_inline)) void f(L *head, int inc) { while (head) { asm volatile ("// Loop %0" :: "i" (N)); int subinc = head->data + inc; if (__builtin_expect_with_probability (bool(head->inner), 0, PROB)) S<N-1>::f(head->inner, subinc); head->data = subinc; head = head->inner; } } }; template<> struct S<0> { static void f(L *, int) { asm volatile ("// foo" ::: "x0", "x1", "x2", "x3", "x4", "x5", "x6", "x7"); } }; void x(L *head) { S<10>::f(head, 1); } --------------------------------------------------------------------- compiled on aarch64 with -O3, we always seem to spill in the outer loops regardless of the value of PROB. That is, the inner loops always seem to get priority even if their bb frequencies are low. I would have expected that moving PROB from 0.05 (inner loop very likely to be executed) to 0.95 (inner loop very likely to be skipped) would have moved the spills from the outer loops to the inner loops. An unrelated issue on aarch64 is that IP0 and IP1 are explicitly clobbered by call instructions, via CALL_INSN_FUNCTION_USAGE. We have to do this because the linker is allowed to insert code that clobbers those registers even if we “know” that the target of the call doesn't clobber them. However, clobbering the registers that way prevents them from being used for registers that are live across the call, even if the call is very unlikely to be executed. Hacking a fix for that does reduce the number of spills, but doesn't get rid of the ones that matter in exchange2.
next prev parent reply other threads:[~2021-12-20 18:06 UTC|newest] Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-01-21 14:31 [Bug rtl-optimization/98782] New: IRA artificially creating spills due to " tnfchris at gcc dot gnu.org 2021-01-21 14:35 ` [Bug rtl-optimization/98782] " jgreenhalgh at gcc dot gnu.org 2021-01-22 10:12 ` fxue at os dot amperecomputing.com 2021-01-29 13:34 ` tnfchris at gcc dot gnu.org 2021-02-05 12:02 ` [Bug rtl-optimization/98782] [11 Regression] Bad interaction between IPA frequences and IRA resulting in spills due to changes in " tnfchris at gcc dot gnu.org 2021-02-23 2:11 ` jiangning.liu at amperecomputing dot com 2021-02-23 12:06 ` rguenth at gcc dot gnu.org 2021-02-26 12:32 ` rguenth at gcc dot gnu.org 2021-11-28 19:07 ` [Bug rtl-optimization/98782] [11/12 " hubicka at gcc dot gnu.org 2021-11-29 1:33 ` jiangning.liu at amperecomputing dot com 2021-11-29 6:59 ` tnfchris at gcc dot gnu.org 2021-12-03 11:44 ` hubicka at gcc dot gnu.org 2021-12-03 11:47 ` hubicka at gcc dot gnu.org 2021-12-07 11:19 ` tnfchris at gcc dot gnu.org 2021-12-07 11:21 ` tnfchris at gcc dot gnu.org 2021-12-07 11:21 ` tnfchris at gcc dot gnu.org 2021-12-07 19:44 ` rsandifo at gcc dot gnu.org 2021-12-07 23:52 ` tnfchris at gcc dot gnu.org 2021-12-08 9:33 ` rsandifo at gcc dot gnu.org 2021-12-08 14:31 ` tnfchris at gcc dot gnu.org 2021-12-08 15:02 ` rsandifo at gcc dot gnu.org 2021-12-09 19:56 ` pthaugen at gcc dot gnu.org 2021-12-09 20:12 ` hubicka at gcc dot gnu.org 2021-12-09 21:27 ` pthaugen at gcc dot gnu.org 2021-12-10 11:36 ` hubicka at gcc dot gnu.org 2021-12-14 14:38 ` tnfchris at gcc dot gnu.org 2021-12-14 14:40 ` hubicka at kam dot mff.cuni.cz 2021-12-14 14:48 ` tnfchris at gcc dot gnu.org 2021-12-14 14:58 ` hubicka at kam dot mff.cuni.cz 2021-12-14 15:07 ` tnfchris at gcc dot gnu.org 2021-12-14 15:08 ` tnfchris at gcc dot gnu.org 2021-12-14 18:16 ` jamborm at gcc dot gnu.org 2021-12-15 12:15 ` tnfchris at gcc dot gnu.org 2021-12-20 18:06 ` rsandifo at gcc dot gnu.org [this message] 2021-12-31 17:28 ` rsandifo at gcc dot gnu.org 2022-01-04 22:26 ` pthaugen at gcc dot gnu.org 2022-01-04 22:29 ` pthaugen at gcc dot gnu.org 2022-01-06 14:53 ` rsandifo at gcc dot gnu.org 2022-01-10 1:29 ` crazylht at gmail dot com 2022-01-11 10:14 ` Jan Hubicka 2022-01-10 14:47 ` cvs-commit at gcc dot gnu.org 2022-01-10 14:47 ` cvs-commit at gcc dot gnu.org 2022-01-10 14:47 ` cvs-commit at gcc dot gnu.org 2022-01-10 14:47 ` cvs-commit at gcc dot gnu.org 2022-01-10 14:52 ` [Bug rtl-optimization/98782] [11 " rsandifo at gcc dot gnu.org 2022-01-11 10:14 ` hubicka at kam dot mff.cuni.cz 2022-01-11 14:22 ` rsandifo at gcc dot gnu.org
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