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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/96270] [8/9/10/11 Regression] stdarg malfunction with -m32 and -Os Date: Wed, 22 Jul 2020 08:28:42 +0000 [thread overview] Message-ID: <bug-96270-4-2yGNYwC6WT@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-96270-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96270 --- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- Note the complication is that u.r is of type 'double' and thus DFmode which has a mode precision of 64. So this is once again the x86 backend using float loads/stores that are value-changing (IIRC the ABI specifies passing 'double' as long double. So the IL "lies" here and "fixing" this would pessimize targets that do not lie for no good reason. (insn 13 12 14 4 (set (mem:DI (pre_dec:SI (reg/f:SI 7 sp)) [0 S8 A64]) (subreg:DI (reg:DF 84 [ pretmp_11 ]) 0)) "t.c":21:5 50 {*pushdi2} (expr_list:REG_ARGS_SIZE (const_int 12 [0xc]) (nil))) (what's this REG_ARGS_SIZE?) eventually gets after LRA (insn 35 6 7 2 (set (mem/c:DF (plus:SI (reg/f:SI 6 bp) (const_int -16 [0xfffffffffffffff0])) [7 %sfp+-8 S8 A64]) (reg:DF 8 st [orig:84 pretmp_11 ] [84])) "t.c":21:5 135 {*movdf_internal} (nil)) ... (insn 13 12 14 3 (set (mem:DI (pre_dec:SI (reg/f:SI 7 sp)) [0 S8 A64]) (mem/c:DI (plus:SI (reg/f:SI 6 bp) (const_int -16 [0xfffffffffffffff0])) [7 %sfp+-8 S8 A64])) "t.c":21:5 50 {*pushdi2} clearly inheritance could somehow have picked up (insn 6 3 35 2 (set (reg:DF 8 st [orig:84 pretmp_11 ] [84]) (mem/j:DF (reg/v/f:SI 0 ax [orig:86 p ] [86]) [4 p_6(D)->u.r+0 S8 A32])) "t.c":21:5 135 {*movdf_internal} (nil)) instead but it really looks like the targets fault. It's unfortunately not possible to fix the code hoisting side without also pessimizing valid CSE where desirable. Maybe we need a new target hook like targetm.can_ldst_unaltered_bits (machine_mode) and x86 has to say no for all x87 modes but long double? It also means that spilling would alter values (but IIRC we always _spill_ via long double).
next prev parent reply other threads:[~2020-07-22 8:28 UTC|newest] Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-21 16:06 [Bug c/96270] New: " drh at sqlite dot org 2020-07-21 16:41 ` [Bug c/96270] " mikpelinux at gmail dot com 2020-07-21 16:55 ` [Bug c/96270] [8/9/10/11 Regression] " jakub at gcc dot gnu.org 2020-07-22 7:53 ` [Bug tree-optimization/96270] " rguenth at gcc dot gnu.org 2020-07-22 8:28 ` rguenth at gcc dot gnu.org [this message] 2020-08-04 9:29 ` rguenth at gcc dot gnu.org 2020-08-04 9:29 ` rguenth at gcc dot gnu.org
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