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 25C1C388A41D for ; Thu, 17 Dec 2020 16:46:30 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 25C1C388A41D 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 17445AC90; Thu, 17 Dec 2020 16:46:29 +0000 (UTC) Subject: [PING^2][PATCH][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> Message-ID: Date: Thu, 17 Dec 2020 17:46:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: <61a5732c-419a-3f48-328d-a941dbc04a80@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.0 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, 17 Dec 2020 16:46:31 -0000 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^2. 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; >> +} >>