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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/113787] [12/13/14 Regression] Wrong code at -O with ipa-modref on aarch64 Date: Tue, 13 Feb 2024 09:21:38 +0000 [thread overview] Message-ID: <bug-113787-4-XiDXU6GLA5@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-113787-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113787 --- Comment #14 from rguenther at suse dot de <rguenther at suse dot de> --- On Tue, 13 Feb 2024, hubicka at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113787 > > --- Comment #13 from Jan Hubicka <hubicka at gcc dot gnu.org> --- > So my understanding is that ivopts does something like > > offset = &base2 - &base1 > > and then translate > val = base2[i] > to > val = *((base1+i)+offset) > > Where (base1+i) is then an iv variable. > > I wonder if we consider doing memory reference with base changed via offset a > valid transformation. Is there way to tell when this happens? IVOPTs does the above but it does it (or should) as offset = (uintptr)&base2 - (uintptr)&base1; val = *((T *)((uintptr)base1 + i + offset)) which is OK for points-to as no POINTER_PLUS_EXPR is involved so the resulting pointer points to both base1 and base2 (which isn't optimal but correct). If we somehow get back a POINTER_PLUS that's where things go wrong. Doing the above in C code would be valid input so we have to treat it correctly (OK, the standard only allows back-and-forth pointer-to-integer casts w/o any adjustment, but of course we relax this). IVOPTs then in putting all of the stuff into 'offset' gets at trying a TARGET_MEM_REF based on a NULL base but that's invalid. We then resort to a LEA (ADDR_EXPR of TARGET_MEM_REF) to compute the address which gets us into some phishy argument that it's not valid to decompose ADDR_EXPR of TARGET_MEM_REF to POINTER_PLUS of the TARGET_MEM_REF base and the offset. But that's how it is (points-to treats (address of) TARGET_MEM_REF as pointing to anything ...). > A quick fix would be to run IPA modref before ivopts, but I do not see how such > transformation can work with rest of alias analysis (PTA etc) It does. Somewhere IPA modref interprets things wrongly, I didn't figure out here though.
next prev parent reply other threads:[~2024-02-13 9:21 UTC|newest] Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top 2024-02-06 13:40 [Bug tree-optimization/113787] New: [14 " acoplan at gcc dot gnu.org 2024-02-06 13:49 ` [Bug tree-optimization/113787] " jakub at gcc dot gnu.org 2024-02-06 13:56 ` pinskia at gcc dot gnu.org 2024-02-06 13:57 ` acoplan at gcc dot gnu.org 2024-02-06 14:07 ` acoplan at gcc dot gnu.org 2024-02-06 14:13 ` [Bug tree-optimization/113787] [12/13/14 " jakub at gcc dot gnu.org 2024-02-06 14:19 ` pinskia at gcc dot gnu.org 2024-02-06 14:23 ` acoplan at gcc dot gnu.org 2024-02-06 15:41 ` hubicka at gcc dot gnu.org 2024-02-06 16:18 ` pinskia at gcc dot gnu.org 2024-02-07 8:48 ` rguenth at gcc dot gnu.org 2024-02-07 8:49 ` rguenth at gcc dot gnu.org 2024-02-08 14:40 ` acoplan at gcc dot gnu.org 2024-02-13 9:03 ` hubicka at gcc dot gnu.org 2024-02-13 9:21 ` rguenther at suse dot de [this message] 2024-02-13 18:21 ` hubicka at ucw dot cz 2024-02-14 8:19 ` rguenther at suse dot de 2024-02-14 15:07 ` Jan Hubicka 2024-02-14 15:07 ` hubicka at ucw dot cz 2024-02-14 15:09 ` rguenther at suse dot de 2024-02-14 15:18 ` hubicka at ucw dot cz 2024-05-16 9:07 ` [Bug tree-optimization/113787] [12/13/14/15 " acoplan at gcc dot gnu.org 2024-05-16 13:34 ` cvs-commit at gcc dot gnu.org 2024-05-16 13:39 ` [Bug tree-optimization/113787] [12/13/14 " hubicka at gcc dot gnu.org
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