From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by sourceware.org (Postfix) with ESMTPS id D969239574CD for ; Thu, 29 Apr 2021 12:38:55 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org D969239574CD Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tdevries@suse.de X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id C6CF5AF1A; Thu, 29 Apr 2021 12:38:54 +0000 (UTC) Subject: [committed][omp, simt] Handle alternative IV From: Tom de Vries To: gcc-patches@gcc.gnu.org Cc: Jakub Jelinek , Alexander Monakov References: <20201002132102.GA22373@delia> <61a5732c-419a-3f48-328d-a941dbc04a80@suse.de> <4fde92b4-d893-790e-fe52-83265a51c107@suse.de> Message-ID: Date: Thu, 29 Apr 2021 14:38:54 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.1 MIME-Version: 1.0 In-Reply-To: <4fde92b4-d893-790e-fe52-83265a51c107@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.2 required=5.0 tests=BAYES_00, GIT_PATCH_0, KAM_DMARC_STATUS, RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL, 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: , X-List-Received-Date: Thu, 29 Apr 2021 12:38:58 -0000 On 4/22/21 1:46 PM, Tom de Vries wrote: > On 12/17/20 5:46 PM, Tom de Vries wrote: >> On 10/15/20 5:05 PM, Tom de Vries wrote: >>> On 10/2/20 3:21 PM, Tom de Vries wrote: >>>> Hi, >>>> >>>> Consider the test-case libgomp.c/pr81778.c added in this commit, with >>>> this core loop (note: CANARY_SIZE set to 0 for simplicity): >>>> ... >>>> int s = 1; >>>> #pragma omp target simd >>>> for (int i = N - 1; i > -1; i -= s) >>>> a[i] = 1; >>>> ... >>>> which, given that N is 32, sets a[0..31] to 1. >>>> >>>> After omp-expand, this looks like: >>>> ... >>>> : >>>> simduid.7 = .GOMP_SIMT_ENTER (simduid.7); >>>> .omp_simt.8 = .GOMP_SIMT_ENTER_ALLOC (simduid.7); >>>> D.3193 = -s; >>>> s.9 = s; >>>> D.3204 = .GOMP_SIMT_LANE (); >>>> D.3205 = -s.9; >>>> D.3206 = (int) D.3204; >>>> D.3207 = D.3205 * D.3206; >>>> i = D.3207 + 31; >>>> D.3209 = 0; >>>> D.3210 = -s.9; >>>> D.3211 = D.3210 - i; >>>> D.3210 = -s.9; >>>> D.3212 = D.3211 / D.3210; >>>> D.3213 = (unsigned int) D.3212; >>>> D.3213 = i >= 0 ? D.3213 : 0; >>>> >>>> : >>>> if (D.3209 < D.3213) >>>> goto ; [87.50%] >>>> else >>>> goto ; [12.50%] >>>> >>>> : >>>> a[i] = 1; >>>> D.3215 = -s.9; >>>> D.3219 = .GOMP_SIMT_VF (); >>>> D.3216 = (int) D.3219; >>>> D.3220 = D.3215 * D.3216; >>>> i = D.3220 + i; >>>> D.3209 = D.3209 + 1; >>>> goto ; [100.00%] >>>> ... >>>> >>>> On nvptx, the first time bb6 is executed, i is in the 0..31 range (depending >>>> on the lane that is executing) at bb entry. >>>> >>>> So we have the following sequence: >>>> - a[0..31] is set to 1 >>>> - i is updated to -32..-1 >>>> - D.3209 is updated to 1 (being 0 initially) >>>> - bb19 is executed, and if condition (D.3209 < D.3213) == (1 < 32) evaluates >>>> to true >>>> - bb6 is once more executed, which should not happen because all the elements >>>> that needed to be handled were already handled. >>>> - consequently, elements that should not be written are written >>>> - with CANARY_SIZE == 0, we may run into a libgomp error: >>>> ... >>>> libgomp: cuCtxSynchronize error: an illegal memory access was encountered >>>> ... >>>> and with CANARY_SIZE unmodified, we run into: >>>> ... >>>> Expected 0, got 1 at base[-961] >>>> Aborted (core dumped) >>>> ... >>>> >>>> The cause of this is as follows: >>>> - because the step s is a variable rather than a constant, an alternative >>>> IV (D.3209 in our example) is generated in expand_omp_simd, and the >>>> loop condition is tested in terms of the alternative IV rather than >>>> the original IV (i in our example). >>>> - the SIMT code in expand_omp_simd works by modifying step and initial value. >>>> - The initial value fd->loop.n1 is loaded into a variable n1, which is >>>> modified by the SIMT code and then used there-after. >>>> - The step fd->loop.step is loaded into a variable step, which is is modified >>>> by the SIMT code, but afterwards there are uses of both step and >>>> fd->loop.step. >>>> - There are uses of fd->loop.step in the alternative IV handling code, >>>> which should use step instead. >>>> >>>> Fix this by introducing an additional variable orig_step, which is not >>>> modified by the SIMT code and replacing all remaining uses of fd->loop.step >>>> by either step or orig_step. >>>> >>>> Build on x86_64-linux with nvptx accelerator, tested libgomp. >>>> >>>> This fixes for-5.c and for-6.c FAILs I'm currently seeing on a quadro m1200 >>>> with driver 450.66. >>>> >>>> OK for trunk? >>>> >>> > > Ping^3. > Committed. Thanks, - Tom >>>> [omp, simt] Handle alternative IV >>>> >>>> gcc/ChangeLog: >>>> >>>> 2020-10-02 Tom de Vries >>>> >>>> * omp-expand.c (expand_omp_simd): Add step_orig, and replace uses of >>>> fd->loop.step by either step or orig_step. >>>> >>>> libgomp/ChangeLog: >>>> >>>> 2020-10-02 Tom de Vries >>>> >>>> * testsuite/libgomp.c/pr81778.c: New test. >>>> >>>> --- >>>> gcc/omp-expand.c | 11 ++++---- >>>> libgomp/testsuite/libgomp.c/pr81778.c | 48 +++++++++++++++++++++++++++++++++++ >>>> 2 files changed, 54 insertions(+), 5 deletions(-) >>>> >>>> diff --git a/gcc/omp-expand.c b/gcc/omp-expand.c >>>> index 99cb4f9dda4..80e35ac0294 100644 >>>> --- a/gcc/omp-expand.c >>>> +++ b/gcc/omp-expand.c >>>> @@ -6307,6 +6307,7 @@ expand_omp_simd (struct omp_region *region, struct omp_for_data *fd) >>>> n2 = OMP_CLAUSE_DECL (innerc); >>>> } >>>> tree step = fd->loop.step; >>>> + tree orig_step = step; /* May be different from step if is_simt. */ >>>> >>>> bool is_simt = omp_find_clause (gimple_omp_for_clauses (fd->for_stmt), >>>> OMP_CLAUSE__SIMT_); >>>> @@ -6455,7 +6456,7 @@ expand_omp_simd (struct omp_region *region, struct omp_for_data *fd) >>>> tree altv = NULL_TREE, altn2 = NULL_TREE; >>>> if (fd->collapse == 1 >>>> && !broken_loop >>>> - && TREE_CODE (fd->loops[0].step) != INTEGER_CST) >>>> + && TREE_CODE (orig_step) != INTEGER_CST) >>>> { >>>> /* The vectorizer currently punts on loops with non-constant steps >>>> for the main IV (can't compute number of iterations and gives up >>>> @@ -6471,7 +6472,7 @@ expand_omp_simd (struct omp_region *region, struct omp_for_data *fd) >>>> itype = signed_type_for (itype); >>>> t = build_int_cst (itype, (fd->loop.cond_code == LT_EXPR ? -1 : 1)); >>>> t = fold_build2 (PLUS_EXPR, itype, >>>> - fold_convert (itype, fd->loop.step), t); >>>> + fold_convert (itype, step), t); >>>> t = fold_build2 (PLUS_EXPR, itype, t, fold_convert (itype, n2)); >>>> t = fold_build2 (MINUS_EXPR, itype, t, >>>> fold_convert (itype, fd->loop.v)); >>>> @@ -6479,10 +6480,10 @@ expand_omp_simd (struct omp_region *region, struct omp_for_data *fd) >>>> t = fold_build2 (TRUNC_DIV_EXPR, itype, >>>> fold_build1 (NEGATE_EXPR, itype, t), >>>> fold_build1 (NEGATE_EXPR, itype, >>>> - fold_convert (itype, fd->loop.step))); >>>> + fold_convert (itype, step))); >>>> else >>>> t = fold_build2 (TRUNC_DIV_EXPR, itype, t, >>>> - fold_convert (itype, fd->loop.step)); >>>> + fold_convert (itype, step)); >>>> t = fold_convert (TREE_TYPE (altv), t); >>>> altn2 = create_tmp_var (TREE_TYPE (altv)); >>>> expand_omp_build_assign (&gsi, altn2, t); >>>> @@ -6630,7 +6631,7 @@ expand_omp_simd (struct omp_region *region, struct omp_for_data *fd) >>>> if (is_simt) >>>> { >>>> gsi = gsi_start_bb (l2_bb); >>>> - step = fold_build2 (MINUS_EXPR, TREE_TYPE (step), fd->loop.step, step); >>>> + step = fold_build2 (MINUS_EXPR, TREE_TYPE (step), orig_step, step); >>>> if (POINTER_TYPE_P (type)) >>>> t = fold_build_pointer_plus (fd->loop.v, step); >>>> else >>>> diff --git a/libgomp/testsuite/libgomp.c/pr81778.c b/libgomp/testsuite/libgomp.c/pr81778.c >>>> new file mode 100644 >>>> index 00000000000..571668eb36a >>>> --- /dev/null >>>> +++ b/libgomp/testsuite/libgomp.c/pr81778.c >>>> @@ -0,0 +1,48 @@ >>>> +/* Minimized from for-5.c. */ >>>> + >>>> +#include >>>> +#include >>>> + >>>> +/* Size of array we want to write. */ >>>> +#define N 32 >>>> + >>>> +/* Size of extra space before and after. */ >>>> +#define CANARY_SIZE (N * 32) >>>> + >>>> +/* Start of array we want to write. */ >>>> +#define BASE (CANARY_SIZE) >>>> + >>>> +// Total size to be allocated. >>>> +#define ALLOC_SIZE (CANARY_SIZE + N + CANARY_SIZE) >>>> + >>>> +#pragma omp declare target >>>> +int a[ALLOC_SIZE]; >>>> +#pragma omp end declare target >>>> + >>>> +int >>>> +main (void) >>>> +{ >>>> + /* Use variable step in for loop. */ >>>> + int s = 1; >>>> + >>>> +#pragma omp target update to(a) >>>> + >>>> + /* Write a[BASE] .. a[BASE + N - 1]. */ >>>> +#pragma omp target simd >>>> + for (int i = N - 1; i > -1; i -= s) >>>> + a[BASE + i] = 1; >>>> + >>>> +#pragma omp target update from(a) >>>> + >>>> + for (int i = 0; i < ALLOC_SIZE; i++) >>>> + { >>>> + int expected = (BASE <= i && i < BASE + N) ? 1 : 0; >>>> + if (a[i] == expected) >>>> + continue; >>>> + >>>> + printf ("Expected %d, got %d at base[%d]\n", expected, a[i], i - BASE); >>>> + abort (); >>>> + } >>>> + >>>> + return 0; >>>> +} >>>>