From patchwork Thu Jul 8 09:53:37 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Roger Sayle X-Patchwork-Id: 1502156 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+incoming=patchwork.ozlabs.org@gcc.gnu.org; receiver=) Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=nextmovesoftware.com header.i=@nextmovesoftware.com header.a=rsa-sha256 header.s=default header.b=AwU4eCds; dkim-atps=neutral Received: from sourceware.org (ip-8-43-85-97.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 4GLBTB0l4bz9sWl for ; Thu, 8 Jul 2021 19:54:06 +1000 (AEST) Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id A13AA3982414 for ; Thu, 8 Jul 2021 09:54:03 +0000 (GMT) X-Original-To: gcc-patches@gcc.gnu.org Delivered-To: gcc-patches@gcc.gnu.org Received: from server.nextmovesoftware.com (server.nextmovesoftware.com [162.254.253.69]) by sourceware.org (Postfix) with ESMTPS id E3631395700F for ; Thu, 8 Jul 2021 09:53:38 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org E3631395700F Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=nextmovesoftware.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=nextmovesoftware.com DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=nextmovesoftware.com; s=default; h=Content-Type:MIME-Version:Message-ID: Date:Subject:To:From:Sender:Reply-To:Cc:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:In-Reply-To:References:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=mK58bedvv8Nuw6r3PiR1THDy2dQ4/Qvr7RA8law7OlI=; b=AwU4eCdsT1gXpj8WB9SozVhuZj IMl11AvNgHOTBK/1LBMXbBh0Jrv35a4Mo/il0H9QpVR3snC6Vg72iNx/NGyKaKbCx0rmtIZJJM0XA TAGtB5ys/+CtZdJfrmWUThuf+a3CkqRD1HVcv1KtzVZlZ/Q1Zr87gYFGDZ2BpMSMuNhC84sQdRwuD Sw1lVGKJWrq+0z3+XobkhmMUPI+b51Gvl4tOG9sRcusIe8AYxfdNVfec3fK9mZtZVghw+3EfANEh7 fztOyKSKrAr724YShdhV1RipD4LZOZw2/H8MK85TOqW2dLuWEnbNTQozjIZQi+V8W06Ig7Q0jpWd0 fc+3Onew==; Received: from host86-169-60-32.range86-169.btcentralplus.com ([86.169.60.32]:52839 helo=Dell) by server.nextmovesoftware.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1m1Qiw-0000UY-CW for gcc-patches@gcc.gnu.org; Thu, 08 Jul 2021 05:53:38 -0400 From: "Roger Sayle" To: "'GCC Patches'" Subject: [PATCH] PR tree-optimization/38943: Preserve trapping instructions with -fnon-call-exceptions Date: Thu, 8 Jul 2021 10:53:37 +0100 Message-ID: <002a01d773df$202b5150$6081f3f0$@nextmovesoftware.com> MIME-Version: 1.0 X-Mailer: Microsoft Outlook 16.0 Thread-Index: Addz3j28a/SqhhFiRi67Uz7G3aRtlg== Content-Language: en-gb X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - server.nextmovesoftware.com X-AntiAbuse: Original Domain - gcc.gnu.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - nextmovesoftware.com X-Get-Message-Sender-Via: server.nextmovesoftware.com: authenticated_id: roger@nextmovesoftware.com X-Authenticated-Sender: server.nextmovesoftware.com: roger@nextmovesoftware.com X-Source: X-Source-Args: X-Source-Dir: X-Spam-Status: No, score=-12.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) 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: , Errors-To: gcc-patches-bounces+incoming=patchwork.ozlabs.org@gcc.gnu.org Sender: "Gcc-patches" This patch addresses PR tree-optimization/38943 where gcc may optimize away trapping instructions even when -fnon-call-exceptions is specified. Interestingly this only affects the C compiler (when -fexceptions is not specified) as g++ (or -fexceptions) supports C++-style exception handling, where -fnon-call-exceptions triggers the stmt_could_throw_p machinery. Without -fexceptions, trapping instructions aren't always considered visible side-effects. This patch fixes this in two place. Firstly, gimple_has_side_effects is tweaked such that gimple_could_trap_p is considered a side-effect if the current function can throw non-call exceptions. And secondly, check_stmt in ipa-pure-const.c is tweaked such that a function containing a trapping statement is considered to have a side-effect with -fnon-call-exceptions, and therefore cannot be pure or const. Calling gimple_could_trap_p (which previously took a non-const gimple) from gimple_has_side_effects (which takes a const gimple) required improving the const-safety of gimple_could_trap_p (a relatively minor tweak) and its prototypes. Hopefully this is considered a clean-up/ improvement. This patch has been tested on x86_64-pc-linux-gnu with a "make bootstrap" and "make -k check" with no new failures. This should be relatively safe, as there are no changes in behaviour unless the user explicitly specifies -fnon-call-exceptions, when the C compiler then behaves more like the C++/Ada compiler. Ok for mainline? 2021-07-08 Roger Sayle gcc/ChangeLog PR tree-optimization/38943 * gimple.c (gimple_has_side_effects): Consider trapping to be a side-effect when -fnon-call-exceptions is specified. (gimple_coult_trap_p_1): Make S argument a "const gimple*". Preserve constness in call to gimple_asm_volatile_p. (gimple_could_trap_p): Make S argument a "const gimple*". * gimple.h (gimple_could_trap_p_1, gimple_could_trap_p): Update function prototypes. * ipa-pure-const.c (check_stmt): When the current function can throw non-call exceptions, a trapping statement should be considered a side-effect, so the function is neither const nor pure. gcc/testsuite/ChangeLog PR tree-optimization/38943 * gcc.dg/pr38943.c: New test case. Roger --- Roger Sayle NextMove Software Cambridge, UK /* { dg-do compile } */ /* { dg-options "-O2 -fnon-call-exceptions -fdump-tree-optimized" } */ float __attribute__((noinline)) foo (float x) { return 2.0f / x; }; void bar() { foo (3.0f); } /* { dg-final { scan-tree-dump "foo \\(3" "optimized" } } */ diff --git a/gcc/gimple.c b/gcc/gimple.c index f1044e9..4b150b0 100644 --- a/gcc/gimple.c +++ b/gcc/gimple.c @@ -2090,7 +2090,8 @@ gimple_move_vops (gimple *new_stmt, gimple *old_stmt) statement to have side effects if: - It is a GIMPLE_CALL not marked with ECF_PURE or ECF_CONST. - - Any of its operands are marked TREE_THIS_VOLATILE or TREE_SIDE_EFFECTS. */ + - Any of its operands are marked TREE_THIS_VOLATILE or TREE_SIDE_EFFECTS. + - It may trap and -fnon-call-exceptions has been specified. */ bool gimple_has_side_effects (const gimple *s) @@ -2108,6 +2109,10 @@ gimple_has_side_effects (const gimple *s) && gimple_asm_volatile_p (as_a (s))) return true; + if (cfun->can_throw_non_call_exceptions + && gimple_could_trap_p (s)) + return true; + if (is_gimple_call (s)) { int flags = gimple_call_flags (s); @@ -2129,7 +2134,7 @@ gimple_has_side_effects (const gimple *s) S is a GIMPLE_ASSIGN, the LHS of the assignment is also checked. */ bool -gimple_could_trap_p_1 (gimple *s, bool include_mem, bool include_stores) +gimple_could_trap_p_1 (const gimple *s, bool include_mem, bool include_stores) { tree t, div = NULL_TREE; enum tree_code op; @@ -2146,7 +2151,7 @@ gimple_could_trap_p_1 (gimple *s, bool include_mem, bool include_stores) switch (gimple_code (s)) { case GIMPLE_ASM: - return gimple_asm_volatile_p (as_a (s)); + return gimple_asm_volatile_p (as_a (s)); case GIMPLE_CALL: t = gimple_call_fndecl (s); @@ -2192,7 +2197,7 @@ gimple_could_trap_p_1 (gimple *s, bool include_mem, bool include_stores) /* Return true if statement S can trap. */ bool -gimple_could_trap_p (gimple *s) +gimple_could_trap_p (const gimple *s) { return gimple_could_trap_p_1 (s, true, true); } diff --git a/gcc/gimple.h b/gcc/gimple.h index e7dc2a4..1a2e120 100644 --- a/gcc/gimple.h +++ b/gcc/gimple.h @@ -1601,8 +1601,8 @@ void gimple_set_lhs (gimple *, tree); gimple *gimple_copy (gimple *); void gimple_move_vops (gimple *, gimple *); bool gimple_has_side_effects (const gimple *); -bool gimple_could_trap_p_1 (gimple *, bool, bool); -bool gimple_could_trap_p (gimple *); +bool gimple_could_trap_p_1 (const gimple *, bool, bool); +bool gimple_could_trap_p (const gimple *); bool gimple_assign_rhs_could_trap_p (gimple *); extern void dump_gimple_statistics (void); unsigned get_gimple_rhs_num_ops (enum tree_code); diff --git a/gcc/ipa-pure-const.c b/gcc/ipa-pure-const.c index f045108..436cbcd 100644 --- a/gcc/ipa-pure-const.c +++ b/gcc/ipa-pure-const.c @@ -765,6 +765,14 @@ check_stmt (gimple_stmt_iterator *gsip, funct_state local, bool ipa) if (dump_file) fprintf (dump_file, " Volatile stmt is not const/pure\n"); } + else if (cfun->can_throw_non_call_exceptions + && gimple_code (stmt) != GIMPLE_CALL + && gimple_could_trap_p (stmt)) + { + local->pure_const_state = IPA_NEITHER; + if (dump_file) + fprintf (dump_file, " Trapping stmt is not const/pure\n"); + } /* Look for loads and stores. */ walk_stmt_load_store_ops (stmt, local,