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Sat, 26 Sep 2026 08:54:16 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Sat, 26 Sep 2026 15:54:15 +0000 Message-Id: From: "Alexei Starovoitov" To: "Eduard Zingerman" , , Cc: , , , , Subject: Re: [PATCH bpf-next 18/36] bpf: compute immediate dominators In-Reply-To: <20260926-scev-minimal-rebase-v1-18-c8e5ab5ba79f@gmail.com> References: <20260926-scev-minimal-rebase-v1-0-c8e5ab5ba79f@gmail.com> <20260926-scev-minimal-rebase-v1-18-c8e5ab5ba79f@gmail.com> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Sat, Sep 26, 2026 at 07:20 AM Eduard Zingerman wrote: > +static int idoms_intersect(struct bpf_verifier_env *env, int a, int b) > +{ > + int *postorder_nums = env->cfg.postorder_nums; > + int *idoms = env->idoms; > + > + while (a != b) { > + while (postorder_nums[a] < postorder_nums[b]) { > + a = idoms[a]; > + } This walks the idom chain one insn at a time. For a prog that is a long run of if (err) goto out; 'out' has N predecessors and compute_subprog_idoms() calls this for each of them. The k-th call walks back over k branches. That's N^2/2 steps, and the outer loop runs at least twice. All of it before do_check(), for every prog, loops or not. Same issue as Daniel's commit 3852e19cb954 fixed just yesterday. SCEV needs dominators only inside loops. Can it be computed for insns with scc != 0 only ? and probably a bound for a big loop body.