From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7B922C982C3 for ; Wed, 16 Sep 2026 13:28:46 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1x6pg7-0001ll-Lh; Wed, 16 Sep 2026 09:28:00 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x6pfx-0001kW-0Q for qemu-devel@nongnu.org; Wed, 16 Sep 2026 09:27:49 -0400 Received: from rev.ng ([94.130.142.21]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x6pfu-0003sV-IJ for qemu-devel@nongnu.org; Wed, 16 Sep 2026 09:27:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=rev.ng; s=dkim; h=Content-Transfer-Encoding:Content-Type:MIME-Version:References: In-Reply-To:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive:List-Unsubscribe:List-Unsubscribe-Post: List-Help; bh=15tu9Igm3t/Cu5fVDuOxFO/Z0eZPJsUUwGHTpW66s+Y=; b=U/Bl0EHToUw4yA2 e8/XfafRB1br2nTuncavnyRm8u//EcJqRIlLQ40fWevmx+N49lewDqwPDR6KzdzQ0lYaSSv/YgDHC gmzoJ8Wabdz8p71+G+ZQ5wmt0OLmsgh7zZdaS4Nupua+mSKfk7iQ3npHYuQLiMstFAGzE1y7bj8Le 6E=; Date: Wed, 16 Sep 2026 15:16:26 +0200 To: Anton Johansson Cc: qemu-devel@nongnu.org, brian.cain@oss.qualcomm.com, pierrick.bouvier@oss.qualcomm.com, philmd@mailo.com Subject: Re: [PATCH v2 23/50] helper-to-tcg: PrepareForTcgPass, remove functions with cycles Message-ID: <20260916151626.03678639@spawn> In-Reply-To: <20260730031025.12926-24-anjo@rev.ng> References: <20260730031025.12926-1-anjo@rev.ng> <20260730031025.12926-24-anjo@rev.ng> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=94.130.142.21; envelope-from=ale@rev.ng; helo=rev.ng X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-to: Alessandro Di Federico From: Alessandro Di Federico via qemu development Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, 30 Jul 2026 05:09:57 +0200 Anton Johansson wrote: > Functions with cycles are removed for two primary reasons: > > * As a simplifying assumption for register allocation which occurs down > the line, and; > > * If a function contains cycles post-optimization neither unrolling or > loop vectorization were deemed beneficial, and the function _might_ be > better suited as a helper anyway. > > Cycles are detected by iterating over Strongly Connected Components > (SCCs) which imply the existence of cycles if a SCC contains more than one > node, or it has a self-edge. I'd move most of the commit message to the documentation of the function. > > Signed-off-by: Anton Johansson > --- > .../PrepareForTcgPass/PrepareForTcgPass.cpp | 34 +++++++++++++++++-- > 1 file changed, 32 insertions(+), 2 deletions(-) > > diff --git a/subprojects/helper-to-tcg/src/PrepareForTcgPass/PrepareForTcgPass.cpp b/subprojects/helper-to-tcg/src/PrepareForTcgPass/PrepareForTcgPass.cpp > index cea6573e41..41f317ed0b 100644 > --- a/subprojects/helper-to-tcg/src/PrepareForTcgPass/PrepareForTcgPass.cpp > +++ b/subprojects/helper-to-tcg/src/PrepareForTcgPass/PrepareForTcgPass.cpp > @@ -17,9 +17,39 @@ > > #include "PrepareForTcgPass.hpp" > > +#include > +#include > +#include > +#include > + > using namespace llvm; > > -PreservedAnalyses PrepareForTcgPass::run(Module &M, ModuleAnalysisManager &MAM) > -{ > +static void removeFunctionsWithLoops(Module &M, ModuleAnalysisManager &MAM) { > + // Iterate over all Strongly Connected Components (SCCs), a SCC implies > + // the existence of loops if: > + // - it has more than one node, or; > + // - it has a self-edge. > + SmallPtrSet FunctionsToRemove; > + for (Function &F : M) { > + if (F.isDeclaration()) { > + continue; > + } > + for (auto It = scc_begin(&F); !It.isAtEnd(); ++It) { > + if (It.hasCycle()) { > + FunctionsToRemove.insert(&F); > + break; > + } > + } > + } > + > + for (Function *F : FunctionsToRemove) { > + F->setComdat(nullptr); > + F->deleteBody(); > + } > +} > + > +PreservedAnalyses PrepareForTcgPass::run(Module &M, > + ModuleAnalysisManager &MAM) { > + removeFunctionsWithLoops(M, MAM); > return PreservedAnalyses::none(); > } > -- > 2.52.0 Reviewed-by: Alessandro Di Federico -- Alessandro Di Federico rev.ng Labs