Hi, Consider test-case pr104952-1.c, included in this commit, containing: ... #pragma omp target map(tofrom:result) map(to:arr) #pragma omp simd reduction(||: result) ...
When run on x86_64 with nvptx accelerator, the test-case either aborts or hangs. The reduction clause is translated by the SIMT code (active for nvptx) as a butterfly reduction loop with this butterfly shuffle / update pair: ... D.2163 = D.2163 || .GOMP_SIMT_XCHG_BFLY (D.2163, D.2164) ... in the loop body. The problem is that the butterfly shuffle is possibly not executed, while it needs to be executed unconditionally. Fix this by translating instead as: ... D.tmp_bfly = .GOMP_SIMT_XCHG_BFLY (D.2163, D.2164) D.2163 = D.2163 || D.tmp_bfly ... Tested on x86_64-linux with nvptx accelerator. Committed to trunk. Thanks, - Tom [openmp] Fix SIMT reduction using TRUTH_{AND,OR}IF_EXPR gcc/ChangeLog: 2022-03-17 Tom de Vries <tdevr...@suse.de> PR target/104952 * omp-low.cc (lower_rec_input_clauses): Make sure GOMP_SIMT_XCHG_BFLY is executed unconditionally. libgomp/ChangeLog: 2022-03-17 Tom de Vries <tdevr...@suse.de> PR target/104952 * testsuite/libgomp.c/pr104952-1.c: New test. * testsuite/libgomp.c/pr104952-2.c: New test. --- gcc/omp-low.cc | 5 ++++- libgomp/testsuite/libgomp.c/pr104952-1.c | 24 ++++++++++++++++++++++++ libgomp/testsuite/libgomp.c/pr104952-2.c | 22 ++++++++++++++++++++++ 3 files changed, 50 insertions(+), 1 deletion(-) diff --git a/gcc/omp-low.cc b/gcc/omp-low.cc index cfc63d6a104..392bb18bc5d 100644 --- a/gcc/omp-low.cc +++ b/gcc/omp-low.cc @@ -6743,7 +6743,10 @@ lower_rec_input_clauses (tree clauses, gimple_seq *ilist, gimple_seq *dlist, x = build_call_expr_internal_loc (UNKNOWN_LOCATION, IFN_GOMP_SIMT_XCHG_BFLY, TREE_TYPE (ivar), 2, ivar, simt_lane); - x = build2 (code, TREE_TYPE (ivar), ivar, x); + /* Make sure x is evaluated unconditionally. */ + tree bfly_var = create_tmp_var (TREE_TYPE (ivar)); + gimplify_assign (bfly_var, x, &llist[2]); + x = build2 (code, TREE_TYPE (ivar), ivar, bfly_var); gimplify_assign (ivar, x, &llist[2]); } tree ivar2 = ivar; diff --git a/libgomp/testsuite/libgomp.c/pr104952-1.c b/libgomp/testsuite/libgomp.c/pr104952-1.c new file mode 100644 index 00000000000..a3bfb1e77df --- /dev/null +++ b/libgomp/testsuite/libgomp.c/pr104952-1.c @@ -0,0 +1,24 @@ +#define N 32 + +static char arr[N]; + +int +main (void) +{ + unsigned int result = 0; + + for (unsigned int i = 0; i < N; ++i) + arr[i] = 0; + + arr[5] = 42; + +#pragma omp target map(tofrom:result) map(to:arr) +#pragma omp simd reduction(||: result) + for (unsigned int i = 0; i < N; ++i) + result = result || arr[i]; + + if (result != 1) + __builtin_abort (); + + return 0; +} diff --git a/libgomp/testsuite/libgomp.c/pr104952-2.c b/libgomp/testsuite/libgomp.c/pr104952-2.c new file mode 100644 index 00000000000..7ab4bcdb8af --- /dev/null +++ b/libgomp/testsuite/libgomp.c/pr104952-2.c @@ -0,0 +1,22 @@ +#define N 32 + +static char arr[N]; + +int +main (void) +{ + unsigned int result = 2; + + for (unsigned int i = 0; i < N; ++i) + arr[i] = i + 1; + +#pragma omp target map(tofrom:result) map(to:arr) +#pragma omp simd reduction(&&: result) + for (unsigned int i = 0; i < N; ++i) + result = result && arr[i]; + + if (result != 1) + __builtin_abort (); + + return 0; +}