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tblahtblah
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[OMPIRBuilder] always leave PARALLEL via the same barrier (#164586)
A barrier will pause execution until all threads reach it. If some go to a different barrier then we deadlock. This manifests in that the finalization callback must only be run once. Fix by ensuring we always go through the same finalization block whether the thread in cancelled or not and no matter which cancellation point causes the cancellation. The old callback only affected PARALLEL, so it has been moved into the code generating PARALLEL. For this reason, we don't need similar changes for other cancellable constructs. We need to create the barrier on the shared exit from the outlined function instead of only on the cancelled branch to make sure that threads exiting normally (without cancellation) meet the same barriers as those which were cancelled. For example, previously we might have generated code like ``` ... %ret = call i32 @__kmpc_cancel(...) %cond = icmp eq i32 %ret, 0 br i1 %cond, label %continue, label %cancel continue: // do the rest of the callback, eventually branching to %fini br label %fini cancel: // Populated by the callback: // unsafe: if any thread makes it to the end without being cancelled // it won't reach this barrier and then the program will deadlock %unused = call i32 @__kmpc_cancel_barrier(...) br label %fini fini: // run destructors etc ret ``` In the new version the barrier is moved into fini. I generate it *after* the destructors because the standard describes the barrier as occurring after the end of the parallel region. ``` ... %ret = call i32 @__kmpc_cancel(...) %cond = icmp eq i32 %ret, 0 br i1 %cond, label %continue, label %cancel continue: // do the rest of the callback, eventually branching to %fini br label %fini cancel: br label %fini fini: // run destructors etc // safe so long as every exit from the function happens via this block: %unused = call i32 @__kmpc_cancel_barrier(...) ret ``` To achieve this, the barrier is now generated alongside the finalization code instead of in the callback. This is the reason for the changes to the unit test. I'm unsure if I should keep the incorrect barrier generation callback only on the cancellation branch in clang with the OMPIRBuilder backend because that would match clang's ordinary codegen. Right now I have opted to remove it entirely because it is a deadlock waiting to happen.
1 parent 4394aa6 commit 0e5633f

23 files changed

+369
-262
lines changed

‎clang/test/OpenMP/cancel_codegen.cpp‎

Lines changed: 20 additions & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -774,8 +774,6 @@ for (int i = 0; i < argc; ++i) {
774774
// CHECK3-NEXT: call void @__kmpc_barrier(ptr @[[GLOB2:[0-9]+]], i32 [[OMP_GLOBAL_THREAD_NUM12]])
775775
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_AFTER:%.*]]
776776
// CHECK3: omp_section_loop.after:
777-
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_AFTERSECTIONS_FINI:%.*]]
778-
// CHECK3: omp_section_loop.aftersections.fini:
779777
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_PREHEADER13:%.*]]
780778
// CHECK3: omp_section_loop.preheader13:
781779
// CHECK3-NEXT: store i32 0, ptr [[P_LOWERBOUND29]], align 4
@@ -811,16 +809,16 @@ for (int i = 0; i < argc; ++i) {
811809
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_BODY_CASE23_SECTION_AFTER:%.*]]
812810
// CHECK3: omp_section_loop.body.case23.section.after:
813811
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_BODY16_SECTIONS_AFTER]]
814-
// CHECK3: omp_section_loop.body.case25:
812+
// CHECK3: omp_section_loop.body.case26:
815813
// CHECK3-NEXT: [[OMP_GLOBAL_THREAD_NUM27:%.*]] = call i32 @__kmpc_global_thread_num(ptr @[[GLOB1]])
816814
// CHECK3-NEXT: [[TMP18:%.*]] = call i32 @__kmpc_cancel(ptr @[[GLOB1]], i32 [[OMP_GLOBAL_THREAD_NUM27]], i32 3)
817815
// CHECK3-NEXT: [[TMP19:%.*]] = icmp eq i32 [[TMP18]], 0
818816
// CHECK3-NEXT: br i1 [[TMP19]], label [[OMP_SECTION_LOOP_BODY_CASE25_SPLIT:%.*]], label [[OMP_SECTION_LOOP_BODY_CASE25_CNCL:%.*]]
819-
// CHECK3: omp_section_loop.body.case25.split:
817+
// CHECK3: omp_section_loop.body.case26.split:
820818
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_BODY_CASE25_SECTION_AFTER26:%.*]]
821-
// CHECK3: omp_section_loop.body.case25.section.after26:
819+
// CHECK3: omp_section_loop.body.case26.section.after27:
822820
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_BODY_CASE25_SECTION_AFTER:%.*]]
823-
// CHECK3: omp_section_loop.body.case25.section.after:
821+
// CHECK3: omp_section_loop.body.case26.section.after:
824822
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_BODY16_SECTIONS_AFTER]]
825823
// CHECK3: omp_section_loop.body16.sections.after:
826824
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_INC17]]
@@ -833,8 +831,6 @@ for (int i = 0; i < argc; ++i) {
833831
// CHECK3-NEXT: call void @__kmpc_barrier(ptr @[[GLOB2]], i32 [[OMP_GLOBAL_THREAD_NUM33]])
834832
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_AFTER19:%.*]]
835833
// CHECK3: omp_section_loop.after19:
836-
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_AFTER19SECTIONS_FINI:%.*]]
837-
// CHECK3: omp_section_loop.after19sections.fini:
838834
// CHECK3-NEXT: [[TMP20:%.*]] = load i32, ptr [[ARGC_ADDR]], align 4
839835
// CHECK3-NEXT: store i32 [[TMP20]], ptr [[DOTCAPTURE_EXPR_]], align 4
840836
// CHECK3-NEXT: [[TMP21:%.*]] = load i32, ptr [[DOTCAPTURE_EXPR_]], align 4
@@ -894,8 +890,8 @@ for (int i = 0; i < argc; ++i) {
894890
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_EXIT]]
895891
// CHECK3: omp_section_loop.body.case23.cncl:
896892
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_EXIT18]]
897-
// CHECK3: omp_section_loop.body.case25.cncl:
898-
// CHECK3-NEXT: br label [[OMP_SECTION_LOOP_EXIT18]]
893+
// CHECK3: omp_section_loop.body.case26.cncl:
894+
// CHECK3-NEXT: br label [[OMP_REGION_FINALIZE:.*]]
899895
// CHECK3: .cancel.continue:
900896
// CHECK3-NEXT: br label [[OMP_IF_END:%.*]]
901897
// CHECK3: omp_if.else:
@@ -967,8 +963,10 @@ for (int i = 0; i < argc; ++i) {
967963
// CHECK3-NEXT: [[TMP8:%.*]] = call i32 @__kmpc_cancel_barrier(ptr @[[GLOB3:[0-9]+]], i32 [[OMP_GLOBAL_THREAD_NUM4]])
968964
// CHECK3-NEXT: [[TMP9:%.*]] = icmp eq i32 [[TMP8]], 0
969965
// CHECK3-NEXT: br i1 [[TMP9]], label [[DOTCONT:%.*]], label [[DOTCNCL5:%.*]]
970-
// CHECK3: .cncl5:
971-
// CHECK3-NEXT: br label [[OMP_PAR_OUTLINED_EXIT_EXITSTUB:%.*]]
966+
// CHECK3: .cncl4:
967+
// CHECK3-NEXT: br label [[FINI:%.*]]
968+
// CHECK3: .fini
969+
// CHECK3-NEXT: br label %[[EXIT_STUB:omp.par.exit.exitStub]]
972970
// CHECK3: .cont:
973971
// CHECK3-NEXT: [[TMP10:%.*]] = load i32, ptr [[LOADGEP_ARGC_ADDR]], align 4
974972
// CHECK3-NEXT: [[TMP11:%.*]] = load ptr, ptr [[LOADGEP_ARGV_ADDR]], align 8
@@ -984,16 +982,14 @@ for (int i = 0; i < argc; ++i) {
984982
// CHECK3: omp.par.region.parallel.after:
985983
// CHECK3-NEXT: br label [[OMP_PAR_PRE_FINALIZE:%.*]]
986984
// CHECK3: omp.par.pre_finalize:
987-
// CHECK3-NEXT: br label [[OMP_PAR_OUTLINED_EXIT_EXITSTUB]]
985+
// CHECK3-NEXT: br label [[FINI]]
988986
// CHECK3: 14:
989987
// CHECK3-NEXT: [[OMP_GLOBAL_THREAD_NUM1:%.*]] = call i32 @__kmpc_global_thread_num(ptr @[[GLOB1]])
990988
// CHECK3-NEXT: [[TMP15:%.*]] = call i32 @__kmpc_cancel(ptr @[[GLOB1]], i32 [[OMP_GLOBAL_THREAD_NUM1]], i32 1)
991989
// CHECK3-NEXT: [[TMP16:%.*]] = icmp eq i32 [[TMP15]], 0
992990
// CHECK3-NEXT: br i1 [[TMP16]], label [[DOTSPLIT:%.*]], label [[DOTCNCL:%.*]]
993991
// CHECK3: .cncl:
994-
// CHECK3-NEXT: [[OMP_GLOBAL_THREAD_NUM2:%.*]] = call i32 @__kmpc_global_thread_num(ptr @[[GLOB1]])
995-
// CHECK3-NEXT: [[TMP17:%.*]] = call i32 @__kmpc_cancel_barrier(ptr @[[GLOB2]], i32 [[OMP_GLOBAL_THREAD_NUM2]])
996-
// CHECK3-NEXT: br label [[OMP_PAR_OUTLINED_EXIT_EXITSTUB]]
992+
// CHECK3-NEXT: br label [[FINI]]
997993
// CHECK3: .split:
998994
// CHECK3-NEXT: br label [[TMP4]]
999995
// CHECK3: omp.par.exit.exitStub:
@@ -1089,7 +1085,7 @@ for (int i = 0; i < argc; ++i) {
10891085
// CHECK3: .omp.sections.case.split:
10901086
// CHECK3-NEXT: br label [[DOTOMP_SECTIONS_EXIT]]
10911087
// CHECK3: .omp.sections.case.cncl:
1092-
// CHECK3-NEXT: br label [[CANCEL_CONT:%.*]]
1088+
// CHECK3-NEXT: br label [[FINI:%.*]]
10931089
// CHECK3: .omp.sections.exit:
10941090
// CHECK3-NEXT: br label [[OMP_INNER_FOR_INC:%.*]]
10951091
// CHECK3: omp.inner.for.inc:
@@ -1100,7 +1096,7 @@ for (int i = 0; i < argc; ++i) {
11001096
// CHECK3: omp.inner.for.end:
11011097
// CHECK3-NEXT: [[OMP_GLOBAL_THREAD_NUM3:%.*]] = call i32 @__kmpc_global_thread_num(ptr @[[GLOB19:[0-9]+]])
11021098
// CHECK3-NEXT: call void @__kmpc_for_static_fini(ptr @[[GLOB15]], i32 [[OMP_GLOBAL_THREAD_NUM3]])
1103-
// CHECK3-NEXT: br label [[CANCEL_CONT]]
1099+
// CHECK3-NEXT: br label [[CANCEL_CONT:.*]]
11041100
// CHECK3: cancel.cont:
11051101
// CHECK3-NEXT: ret void
11061102
// CHECK3: cancel.exit:
@@ -1153,6 +1149,8 @@ for (int i = 0; i < argc; ++i) {
11531149
// CHECK3: .omp.sections.case.split:
11541150
// CHECK3-NEXT: br label [[DOTOMP_SECTIONS_EXIT]]
11551151
// CHECK3: .omp.sections.case.cncl:
1152+
// CHECK3-NEXT: br label [[DOTFINI:.%*]]
1153+
// CHECK3: .fini:
11561154
// CHECK3-NEXT: br label [[CANCEL_CONT:%.*]]
11571155
// CHECK3: .omp.sections.case2:
11581156
// CHECK3-NEXT: [[OMP_GLOBAL_THREAD_NUM3:%.*]] = call i32 @__kmpc_global_thread_num(ptr @[[GLOB1]])
@@ -1162,9 +1160,11 @@ for (int i = 0; i < argc; ++i) {
11621160
// CHECK3: .omp.sections.case2.split:
11631161
// CHECK3-NEXT: br label [[DOTOMP_SECTIONS_CASE2_SECTION_AFTER:%.*]]
11641162
// CHECK3: .omp.sections.case2.section.after:
1165-
// CHECK3-NEXT: br label [[DOTOMP_SECTIONS_EXIT]]
1163+
// CHECK3-NEXT: br label [[OMP_REGION_FINALIZE]]
1164+
// CHECK3: omp_region.finalize:
1165+
// CHECK3-NEXT: br label [[OMP_SECTIONS_EXIT:.*]]
11661166
// CHECK3: .omp.sections.case2.cncl:
1167-
// CHECK3-NEXT: br label [[OMP_INNER_FOR_END]]
1167+
// CHECK3-NEXT: br label [[FINI:.*]]
11681168
// CHECK3: .omp.sections.exit:
11691169
// CHECK3-NEXT: br label [[OMP_INNER_FOR_INC:%.*]]
11701170
// CHECK3: omp.inner.for.inc:

‎clang/test/OpenMP/critical_codegen.cpp‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -35,6 +35,8 @@ int main() {
3535
// ALL-NEXT: store i8 2, ptr [[A_ADDR]]
3636
// IRBUILDER-NEXT: br label %[[AFTER:[^ ,]+]]
3737
// IRBUILDER: [[AFTER]]
38+
// IRBUILDER-NEXT: br label %[[OMP_REGION_FINALIZE:[^ ,]+]]
39+
// IRBUILDER: [[OMP_REGION_FINALIZE]]
3840
// ALL-NEXT: call {{.*}}void @__kmpc_end_critical(ptr [[DEFAULT_LOC]], i32 [[GTID]], ptr [[UNNAMED_LOCK]])
3941
#pragma omp critical
4042
a = 2;

‎clang/test/OpenMP/critical_codegen_attr.cpp‎

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -35,6 +35,8 @@ int main() {
3535
// ALL-NEXT: store i8 2, ptr [[A_ADDR]]
3636
// IRBUILDER-NEXT: br label %[[AFTER:[^ ,]+]]
3737
// IRBUILDER: [[AFTER]]
38+
// IRBUILDER-NEXT: br label %[[OMP_REGION_FINALIZE:[^ ,]+]]
39+
// IRBUILDER: [[OMP_REGION_FINALIZE]]
3840
// ALL-NEXT: call {{.*}}void @__kmpc_end_critical(ptr [[DEFAULT_LOC]], i32 [[GTID]], ptr [[UNNAMED_LOCK]])
3941
[[omp::directive(critical)]]
4042
a = 2;

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