From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 09C76382FADD; Tue, 10 Jan 2023 14:40:48 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 09C76382FADD DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1673361649; bh=ASFX5vEVNOJHHOGdzKrEX3PSsqLMo5y+g2Q8E/wW4ug=; h=From:To:Subject:Date:In-Reply-To:References:From; b=Qde2LE9kIMGmhsCi5sNnuGbb9o/YKdS8eGQ0bqeqTlXPQfVDwruy3LHuE6547mp82 Q/RsFU/f2qbfnuchn9sHOopV0n8glIFPciMJcW5xo2oTE6eopqlOrKP5w20ih1isLK NKXI/zSEKcLL9rW7SuwZfLNX+nO9wAQfpuMCI/Ic= From: "aldyh at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/107608] [13 Regression] Failure on fold-overflow-1.c and pr95115.c Date: Tue, 10 Jan 2023 14:40:48 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 13.0 X-Bugzilla-Keywords: missed-optimization, wrong-code X-Bugzilla-Severity: normal X-Bugzilla-Who: aldyh at gcc dot gnu.org X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P1 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: 13.0 X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 List-Id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107608 --- Comment #24 from Aldy Hernandez --- (In reply to Andrew Macleod from comment #21) > (In reply to Richard Biener from comment #13) >=20 > > Yes, the fact that ranger doesn't operate as a usual propagator with a > > lattice > > makes things very difficult here. Note that my comment referred to code > > optimality, not correctness. > >=20 > > > It really looks like the problem here is DCE (and the gimplifier as y= ou > > > point out in comment #2), which is removing a needed statement. Can'= t this > > > be fixed there? > >=20 > > Sure it can, but the expense is that we'd do constant folding all the w= ay > > down and not remove dead code which will result in _tons_ of unnecessary > > constant pool entries and loads. > >=20 >=20 > I think I'm missing something, or not understanding what you are saying. >=20 > Why is the propagation or lack of lattice a problem? Its DCE that is > removing that potentially trapping stmt because its no longer used in the > IL? THe change would be to not kill off dead statements that may trap? I > guess this may leave a bunch of feeding statements that are not dead.. bu= t I > fail to see how thats different than not propagating and then not being a= ble > to delete those stmts either?=20=20 >=20 >=20 > > The issue is also that -ftrapping-math is default on so we'd have to > > do this by default. Ugh. > >=20 > > Note that the constant folding routines generally refrain from folding > > when that loses exceptions, it's just ranger when producing singleton > > ranges and propagating from them that doesn't adhere to that implicit r= ule. >=20 > I'm also not sure what this means. I don't think ranger itself propagates > singleton constants.. VRP is still using the substitute_and_fold engine, = so > any folding/propagation is still going through the same mechanisms we alw= ays > did when a singleton result is produced. We just produce more of them no= w, > especially with floats. I don't think ranger is doing anything different > than VRP ever did regarding propagation. Its possible GCCs infrastructu= re > for dealing with float propagation isn't mature enough perhaps? Right, ranger isn't propagating anything. It's the substitute_and_fold eng= ine, as it always has, but only if value_of_expr() is non-NULL. Currently this function will only return non-NULL for singletons: tree range_query::value_of_expr (tree expr, gimple *stmt) { tree t; if (!Value_Range::supports_type_p (TREE_TYPE (expr))) return NULL_TREE; Value_Range r (TREE_TYPE (expr)); if (range_of_expr (r, expr, stmt)) { // A constant used in an unreachable block oftens returns as UNDEFINE= D. // If the result is undefined, check the global value for a constant. if (r.undefined_p ()) range_of_expr (r, expr); if (r.singleton_p (&t)) return t; } return NULL_TREE; }=