From patchwork Fri May 7 09:38:23 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: 1475421 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=8.43.85.97; helo=sourceware.org; envelope-from=gcc-patches-bounces@gcc.gnu.org; receiver=) Received: from sourceware.org (server2.sourceware.org [8.43.85.97]) (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 4Fc54F4b2Gz9sj5 for ; Fri, 7 May 2021 19:38:53 +1000 (AEST) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 1A8DF3893672; Fri, 7 May 2021 09:38:30 +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 [205.232.38.15]) by sourceware.org (Postfix) with ESMTP id 1457E389365F for ; Fri, 7 May 2021 09:38:25 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 1457E389365F Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=adacore.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=derodat@adacore.com Received: from localhost (localhost.localdomain [127.0.0.1]) by filtered-rock.gnat.com (Postfix) with ESMTP id 3202C5635C; Fri, 7 May 2021 05:38:23 -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 yuOAxMfCPBj4; Fri, 7 May 2021 05:38:23 -0400 (EDT) Received: from tron.gnat.com (tron.gnat.com [IPv6:2620:20:4000:0:46a8:42ff:fe0e:e294]) by rock.gnat.com (Postfix) with ESMTP id 1E7615635A; Fri, 7 May 2021 05:38:23 -0400 (EDT) Received: by tron.gnat.com (Postfix, from userid 4862) id 1D519FA; Fri, 7 May 2021 05:38:23 -0400 (EDT) Date: Fri, 7 May 2021 05:38:23 -0400 From: Pierre-Marie de Rodat To: gcc-patches@gcc.gnu.org Subject: [Ada] Computation of Shift_Left and large signed values Message-ID: <20210507093823.GA140631@adacore.com> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) X-Spam-Status: No, score=-12.5 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: Arnaud Charlet Errors-To: gcc-patches-bounces@gcc.gnu.org Sender: "Gcc-patches" The computation of Shift_Left on signed values might wrongly overflow instead of generating a negative value. Tested on x86_64-pc-linux-gnu, committed on trunk gcc/ada/ * sem_eval.adb (Fold_Shift): Fix computation of Shift_Left resulting in negative signed values. diff --git a/gcc/ada/sem_eval.adb b/gcc/ada/sem_eval.adb --- a/gcc/ada/sem_eval.adb +++ b/gcc/ada/sem_eval.adb @@ -4983,7 +4983,7 @@ package body Sem_Eval is end if; end Check_Elab_Call; - Modulus : Uint; + Modulus, Val : Uint; begin if Compile_Time_Known_Value (Left) @@ -4994,23 +4994,25 @@ package body Sem_Eval is if Op = N_Op_Shift_Left then Check_Elab_Call; - declare - Modulus : Uint; - begin - if Is_Modular_Integer_Type (Typ) then - Modulus := Einfo.Modulus (Typ); - else - Modulus := Uint_2 ** RM_Size (Typ); - end if; + if Is_Modular_Integer_Type (Typ) then + Modulus := Einfo.Modulus (Typ); + else + Modulus := Uint_2 ** RM_Size (Typ); + end if; - -- Fold Shift_Left (X, Y) by computing (X * 2**Y) rem modulus + -- Fold Shift_Left (X, Y) by computing + -- (X * 2**Y) rem modulus [- Modulus] - Fold_Uint - (N, - (Expr_Value (Left) * (Uint_2 ** Expr_Value (Right))) - rem Modulus, - Static => Static); - end; + Val := (Expr_Value (Left) * (Uint_2 ** Expr_Value (Right))) + rem Modulus; + + if Is_Modular_Integer_Type (Typ) + or else Val < Modulus / Uint_2 + then + Fold_Uint (N, Val, Static => Static); + else + Fold_Uint (N, Val - Modulus, Static => Static); + end if; elsif Op = N_Op_Shift_Right then Check_Elab_Call; @@ -5042,7 +5044,7 @@ package body Sem_Eval is Check_Elab_Call; declare - Two_Y : constant Uint := Uint_2 ** Expr_Value (Right); + Two_Y : constant Uint := Uint_2 ** Expr_Value (Right); begin if Is_Modular_Integer_Type (Typ) then Modulus := Einfo.Modulus (Typ);