From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by sourceware.org (Postfix) with ESMTP id D939F3858D39 for ; Fri, 1 Jul 2022 09:18:45 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org D939F3858D39 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id C141D1063; Fri, 1 Jul 2022 02:18:45 -0700 (PDT) Received: from localhost (e121540-lin.manchester.arm.com [10.32.98.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 09F813F66F; Fri, 1 Jul 2022 02:18:44 -0700 (PDT) From: Richard Sandiford To: Richard Biener via Gcc-patches Mail-Followup-To: Richard Biener via Gcc-patches , Richard Biener , richard.sandiford@arm.com Cc: Richard Biener Subject: Re: [PATCH] tree-optimization/106131 - wrong code with FRE rewriting References: Date: Fri, 01 Jul 2022 10:18:43 +0100 In-Reply-To: (Richard Biener via Gcc-patches's message of "Fri, 1 Jul 2022 06:53:40 +0000 (UTC)") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-56.0 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_NONE, KAM_DMARC_STATUS, KAM_LAZY_DOMAIN_SECURITY, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 01 Jul 2022 09:18:47 -0000 Richard Biener via Gcc-patches writes: > The following makes sure to not use the original TBAA type for > looking up a value across an aggregate copy when we had to offset > the read. > > Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed to trunk. > > 2022-06-30 Richard Biener > > PR tree-optimization/106131 > * tree-ssa-sccvn.cc (vn_reference_lookup_3): Force alias-set > zero when offsetting the read looking through an aggregate > copy. > > * g++.dg/torture/pr106131.C: New testcase. > --- > gcc/testsuite/g++.dg/torture/pr106131.C | 34 +++++++++++++++++++++++++ > gcc/tree-ssa-sccvn.cc | 16 +++++++++--- > 2 files changed, 46 insertions(+), 4 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/torture/pr106131.C > > diff --git a/gcc/testsuite/g++.dg/torture/pr106131.C b/gcc/testsuite/g++.dg/torture/pr106131.C > new file mode 100644 > index 00000000000..e110f4a8fe6 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/torture/pr106131.C > @@ -0,0 +1,34 @@ > +// { dg-do run { target c++11 } } > + > +struct Pair { > + int a, b; > + Pair(const Pair &) = default; > + Pair(int _a, int _b) : a(_a), b(_b) {} > + Pair &operator=(const Pair &z) { > + a = z.a; > + b = z.b; > + return *this; > + } > +}; > + > +const int &max(const int &a, const int &b) > +{ > + return a < b ? b : a; > +} > + > +int foo(Pair x, Pair y) > +{ > + return max(x.b, y.b); > +} > + > +int main() > +{ > + auto f = new Pair[3] {{0, -11}, {0, -8}, {0, 2}}; > + for (int i = 0; i < 1; i++) { > + f[i] = f[0]; > + if(i == 0) > + f[i] = f[2]; > + if (foo(f[i], f[1]) != 2) > + __builtin_abort(); > + } > +} > diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc > index 9deedeac378..76d92895a3a 100644 > --- a/gcc/tree-ssa-sccvn.cc > +++ b/gcc/tree-ssa-sccvn.cc > @@ -3243,12 +3243,12 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, > poly_int64 extra_off = 0; > if (j == 0 && i >= 0 > && lhs_ops[0].opcode == MEM_REF > - && maybe_ne (lhs_ops[0].off, -1)) > + && known_ne (lhs_ops[0].off, -1)) > { > if (known_eq (lhs_ops[0].off, vr->operands[i].off)) > i--, j--; > else if (vr->operands[i].opcode == MEM_REF > - && maybe_ne (vr->operands[i].off, -1)) > + && known_ne (vr->operands[i].off, -1)) These changes don't look right. If -1 is a special marker, it should be tested with known_eq (positive) or maybe_ne (negative). In other words, we should enter the if body if off is not the compile-time constant -1. Thanks, Richard > { > extra_off = vr->operands[i].off - lhs_ops[0].off; > i--, j--; > @@ -3275,6 +3275,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, > copy_reference_ops_from_ref (rhs1, &rhs); > > /* Apply an extra offset to the inner MEM_REF of the RHS. */ > + bool force_no_tbaa = false; > if (maybe_ne (extra_off, 0)) > { > if (rhs.length () < 2) > @@ -3287,6 +3288,10 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, > rhs[ix].op0 = int_const_binop (PLUS_EXPR, rhs[ix].op0, > build_int_cst (TREE_TYPE (rhs[ix].op0), > extra_off)); > + /* When we have offsetted the RHS, reading only parts of it, > + we can no longer use the original TBAA type, force alias-set > + zero. */ > + force_no_tbaa = true; > } > > /* Save the operands since we need to use the original ones for > @@ -3339,8 +3344,11 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_, > /* Adjust *ref from the new operands. */ > ao_ref rhs1_ref; > ao_ref_init (&rhs1_ref, rhs1); > - if (!ao_ref_init_from_vn_reference (&r, ao_ref_alias_set (&rhs1_ref), > - ao_ref_base_alias_set (&rhs1_ref), > + if (!ao_ref_init_from_vn_reference (&r, > + force_no_tbaa ? 0 > + : ao_ref_alias_set (&rhs1_ref), > + force_no_tbaa ? 0 > + : ao_ref_base_alias_set (&rhs1_ref), > vr->type, vr->operands)) > return (void *)-1; > /* This can happen with bitfields. */