From patchwork Tue Feb 7 10:29:26 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Richard Sandiford X-Patchwork-Id: 64437 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 500A73858413 for ; Tue, 7 Feb 2023 10:29:56 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 500A73858413 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1675765796; bh=xpmS/PR1ciuNdy48u80jcSstDuf9yBU/1ZYaiH5VMAA=; h=To:Subject:Date:List-Id:List-Unsubscribe:List-Archive:List-Post: List-Help:List-Subscribe:From:Reply-To:From; b=Xznhma43CyXGsk6zpLqlx73dO4vZl13RxHBsxdx1ZN1zDvMQei+QgXwHmhLogM6fl h59NVGcN/VoXoki82326j11NIIa8+1EN5OocYeTCoFPbPgHIJC1r6u3Wmo8/rEdsQ2 WeSP+YFUr0ymQa1xquiBlgljHrmXCTWjb7wBVsig= X-Original-To: gcc-patches@gcc.gnu.org Delivered-To: gcc-patches@gcc.gnu.org Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by sourceware.org (Postfix) with ESMTP id 67EFC3858D33 for ; Tue, 7 Feb 2023 10:29:28 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 67EFC3858D33 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 64B42106F for ; Tue, 7 Feb 2023 02:30:10 -0800 (PST) Received: from localhost (e121540-lin.manchester.arm.com [10.32.99.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id ACD273F8C6 for ; Tue, 7 Feb 2023 02:29:27 -0800 (PST) To: gcc-patches@gcc.gnu.org Mail-Followup-To: gcc-patches@gcc.gnu.org, richard.sandiford@arm.com Subject: [PATCH] lra: Replace subregs in bare uses & clobbers [PR108681] Date: Tue, 07 Feb 2023 10:29:26 +0000 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Spam-Status: No, score=-35.7 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_NONE, KAM_DMARC_STATUS, KAM_LAZY_DOMAIN_SECURITY, KAM_SHORT, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) 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: , X-Patchwork-Original-From: Richard Sandiford via Gcc-patches From: Richard Sandiford Reply-To: Richard Sandiford Errors-To: gcc-patches-bounces+patchwork=sourceware.org@gcc.gnu.org Sender: "Gcc-patches" In this PR we had a write to one vector of a 4-vector tuple. The vector had mode V1DI, and the target doesn't provide V1DI moves, so this was converted into: (clobber (subreg:V1DI (reg/v:V4x1DI 92 [ b ]) 24)) followed by a DImode move. (The clobber isn't really necessary or helpful for a single word, but would be for wider moves.) The subreg in the clobber survived until after RA: (clobber (subreg:V1DI (reg/v:V4x1DI 34 v2 [orig:92 b ] [92]) 24)) IMO this isn't well-formed. If a subreg of a hard register simplifies to a hard register, it should be replaced by the hard register. If the subreg doesn't simplify, then target-independent code can't be sure which parts of the register are affected and which aren't. A clobber of such a subreg isn't useful and (again IMO) should just be removed. Conversely, a use of such a subreg is effectively a use of the whole inner register. LRA has code to simplify subregs of hard registers, but it didn't handle bare uses and clobbers. The patch extends it to do that. One question was whether the final_p argument to alter_subregs should be true or false. True is IMO dangerous, since it forces replacements that might not be valid from a dataflow perspective, and uses and clobbers only exist for dataflow. As said above, I think the correct way of handling a failed simplification would be to delete clobbers and replace uses of subregs with uses of the inner register. But I didn't want to write untested code to do that. In the PR, the clobber caused an infinite loop in DCE, because of a disagreement about what effect the clobber had. But for the reasons above, I think that was GIGO rather than a bug in DF or DCE. Tested on aarch64-linux-gnu & x86_64-linux-gnu. OK to install? Richard gcc/ PR rtl-optimization/108681 * lra-spills.cc (lra_final_code_change): Extend subreg replacement code to handle bare uses and clobbers. gcc/testsuite/ PR rtl-optimization/108681 * gcc.target/aarch64/pr108681.c: New test. --- gcc/lra-spills.cc | 3 +++ gcc/testsuite/gcc.target/aarch64/pr108681.c | 15 +++++++++++++++ 2 files changed, 18 insertions(+) create mode 100644 gcc/testsuite/gcc.target/aarch64/pr108681.c diff --git a/gcc/lra-spills.cc b/gcc/lra-spills.cc index a8d7e60acd3..4af85c49d43 100644 --- a/gcc/lra-spills.cc +++ b/gcc/lra-spills.cc @@ -860,6 +860,9 @@ lra_final_code_change (void) lra_update_dup (id, i); insn_change_p = true; } + if ((GET_CODE (pat) == USE || GET_CODE (pat) == CLOBBER) + && alter_subregs (&XEXP (pat, 0), false)) + insn_change_p = true; if (insn_change_p) lra_update_operator_dups (id); diff --git a/gcc/testsuite/gcc.target/aarch64/pr108681.c b/gcc/testsuite/gcc.target/aarch64/pr108681.c new file mode 100644 index 00000000000..2391eaac2f2 --- /dev/null +++ b/gcc/testsuite/gcc.target/aarch64/pr108681.c @@ -0,0 +1,15 @@ +/* { dg-options "-O" } */ + +#pragma GCC aarch64 "arm_neon.h" +typedef __Int64x1_t int64x1_t; +void foo (int64x1x4_t); + +void +bar (int64x1_t a) +{ + for (;;) { + int64x1x4_t b; + b.val[3] = a; + foo (b); + } +}