From patchwork Tue Jun 15 10:20:52 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pierre-Marie de Rodat X-Patchwork-Id: 1492115 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org (client-ip=2620:52:3:1:0:246e:9693:128c; helo=sourceware.org; envelope-from=gcc-patches-bounces+incoming=patchwork.ozlabs.org@gcc.gnu.org; receiver=) Received: from sourceware.org (server2.sourceware.org [IPv6:2620:52:3:1:0:246e:9693:128c]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 4G44Qr3fWwz9sW6 for ; Tue, 15 Jun 2021 20:33:08 +1000 (AEST) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id ED24F398B8A5 for ; Tue, 15 Jun 2021 10:33:05 +0000 (GMT) X-Original-To: gcc-patches@gcc.gnu.org Delivered-To: gcc-patches@gcc.gnu.org Received: from rock.gnat.com (rock.gnat.com [IPv6:2620:20:4000:0:a9e:1ff:fe9b:1d1]) by sourceware.org (Postfix) with ESMTPS id 6C5A838515EF for ; Tue, 15 Jun 2021 10:20:56 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 6C5A838515EF Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=adacore.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=adacore.com Received: from localhost (localhost.localdomain [127.0.0.1]) by filtered-rock.gnat.com (Postfix) with ESMTP id EEA02117985; Tue, 15 Jun 2021 06:20:52 -0400 (EDT) X-Virus-Scanned: Debian amavisd-new at gnat.com Received: from rock.gnat.com ([127.0.0.1]) by localhost (rock.gnat.com [127.0.0.1]) (amavisd-new, port 10024) with LMTP id HAFyl+6NUmn7; Tue, 15 Jun 2021 06:20:52 -0400 (EDT) Received: from tron.gnat.com (tron.gnat.com [205.232.38.10]) by rock.gnat.com (Postfix) with ESMTP id B5F2C117B75; Tue, 15 Jun 2021 06:20:52 -0400 (EDT) Received: by tron.gnat.com (Postfix, from userid 4862) id B4BF71CA; Tue, 15 Jun 2021 06:20:52 -0400 (EDT) Date: Tue, 15 Jun 2021 06:20:52 -0400 From: Pierre-Marie de Rodat To: gcc-patches@gcc.gnu.org Subject: [Ada] Avoid unhelpful dead code warnings Message-ID: <20210615102052.GA4383@adacore.com> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Status: No, score=-12.6 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) 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: , Cc: Steve Baird Errors-To: gcc-patches-bounces+incoming=patchwork.ozlabs.org@gcc.gnu.org Sender: "Gcc-patches" We have an existing mechanism for suppressing dead code warning messages in the case of an if-statement within an instance of a generic where the value of the condition is known statically. Generalize this approach to also handle case statements. Tested on x86_64-pc-linux-gnu, committed on trunk gcc/ada/ * exp_util.adb (Kill_Dead_Code): Generalize the existing handling of if statements to handle case statements similarly. diff --git a/gcc/ada/exp_util.adb b/gcc/ada/exp_util.adb --- a/gcc/ada/exp_util.adb +++ b/gcc/ada/exp_util.adb @@ -9238,28 +9238,33 @@ package body Exp_Util is if W then -- We suppress the warning if this code is under control of an - -- if statement, whose condition is a simple identifier, and - -- either we are in an instance, or warnings off is set for this - -- identifier. The reason for killing it in the instance case is - -- that it is common and reasonable for code to be deleted in - -- instances for various reasons. + -- if/case statement and either + -- a) we are in an instance and the condition/selector + -- has a statically known value; or + -- b) the condition/selector is a simple identifier and + -- warnings off is set for this identifier. + -- Dead code is common and reasonable in instances, so we don't + -- want a warning in that case. - -- Could we use Is_Statically_Unevaluated here??? + declare + C : Node_Id := Empty; + begin + if Nkind (Parent (N)) = N_If_Statement then + C := Condition (Parent (N)); + elsif Nkind (Parent (N)) = N_Case_Statement_Alternative then + C := Expression (Parent (Parent (N))); + end if; - if Nkind (Parent (N)) = N_If_Statement then - declare - C : constant Node_Id := Condition (Parent (N)); - begin - if Nkind (C) = N_Identifier - and then - (In_Instance - or else (Present (Entity (C)) - and then Has_Warnings_Off (Entity (C)))) + if Present (C) then + if (In_Instance and Compile_Time_Known_Value (C)) + or else (Nkind (C) = N_Identifier + and then Present (Entity (C)) + and then Has_Warnings_Off (Entity (C))) then W := False; end if; - end; - end if; + end if; + end; -- Generate warning if not suppressed