[OpenMP] Do not SPMDize generic regions with no parallel

[jhuber6]

Summary

This patch changes SPMDization to not trigger for regions with no
parallelism. Otherwise, this will introduce unnecessary barriers that
will slow the single-threaded region down.

[jdoerfert]

LG, one nit

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

602

doxygen documentation, maybe mayContainParallelRegion

[jhuber6]

Addressing nit.

[jdoerfert]

This broke stuff because the Mode is now replaced with SPMD while we actually don't change the _exec_mode of the kernel. Will fix it.

[jdoerfert]

@jhuber6 Can you revert this one for now. Easiest is a new mode I guess. I don't see a good alternative right now.

llvm/lib/Transforms/IPO/OpenMPOpt.cpp

if (ReachedKnownParallelRegions != RHS.ReachedKnownParallelRegions)
       return false;
     if (ReachedUnknownParallelRegions != RHS.ReachedUnknownParallelRegions)
       return false;
     if (ReachingKernelEntries != RHS.ReachingKernelEntries)
       return false;
     return true;
   }
 
+  /// Returns true if this kernel contains any OpenMP parallel regions.
+  bool mayContainParallelRegion() {
+    return !ReachedKnownParallelRegions.empty() ||
+           !ReachedUnknownParallelRegions.empty();
+  }
+
   /// Return empty set as the best state of potential values.
   static KernelInfoState getBestState() { return KernelInfoState(true); }
 
   static KernelInfoState getBestState(KernelInfoState &KIS) {
     return getBestState();
   }
 
   /// Return full set as the worst state of potential values.
if (!KernelInitCB || !KernelDeinitCB)
       return ChangeStatus::UNCHANGED;
 
     // Known SPMD-mode kernels need no manifest changes.
     if (SPMDCompatibilityTracker.isKnown())
       return ChangeStatus::UNCHANGED;
 
     // If we can we change the execution mode to SPMD-mode otherwise we build a
     // custom state machine.
-    if (!changeToSPMDMode(A))
+    if (!mayContainParallelRegion() || !changeToSPMDMode(A))
       buildCustomStateMachine(A);
 
     return ChangeStatus::CHANGED;
   }
 
   bool changeToSPMDMode(Attributor &A) {
     auto &OMPInfoCache = static_cast<OMPInformationCache &>(A.getInfoCache());
 
ChangeStatus buildCustomStateMachine(Attributor &A) {
     auto *FalseVal = ConstantInt::getBool(Ctx, 0);
     A.changeUseAfterManifest(
         KernelInitCB->getArgOperandUse(InitUseStateMachineArgNo), *FalseVal);
 
     // If we don't actually need a state machine we are done here. This can
     // happen if there simply are no parallel regions. In the resulting kernel
     // all worker threads will simply exit right away, leaving the main thread
     // to do the work alone.
-    if (ReachedKnownParallelRegions.empty() &&
-        ReachedUnknownParallelRegions.empty()) {
+    if (!mayContainParallelRegion()) {
       ++NumOpenMPTargetRegionKernelsWithoutStateMachine;
 
       auto Remark = [&](OptimizationRemark OR) {
         return OR << "Removing unused state machine from generic-mode kernel.";
       };
       A.emitRemark<OptimizationRemark>(KernelInitCB, "OMP130", Remark);
 
       return ChangeStatus::CHANGED;

llvm/test/Transforms/OpenMP/always_inline_device.ll

 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-attributes
 ; RUN: opt < %s -S -passes=openmp-opt -openmp-opt-inline-device | FileCheck %s
 
 %struct.ident_t = type { i32, i32, i32, i32, i8* }
 @0 = private unnamed_addr constant [23 x i8] c";unknown;unknown;0;0;;\00", align 1
 @1 = private unnamed_addr constant %struct.ident_t { i32 0, i32 2, i32 0, i32 0, i8* getelementptr inbounds ([23 x i8], [23 x i8]* @0, i32 0, i32 0) }, align 8
 @__omp_offloading_fd02_c0934fc2_foo_l4_exec_mode = weak constant i8 1
 @llvm.compiler.used = appending global [1 x i8*] [i8* @__omp_offloading_fd02_c0934fc2_foo_l4_exec_mode], section "llvm.metadata"
 
 ; Function Attrs: convergent norecurse nounwind
 define weak void @__omp_offloading_fd02_c0934fc2_foo_l4() #0 {
 ; CHECK: Function Attrs: convergent norecurse nounwind
 ; CHECK-LABEL: @__omp_offloading_fd02_c0934fc2_foo_l4(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @__kmpc_target_init(%struct.ident_t* @[[GLOB1:[0-9]+]], i1 true, i1 false, i1 false)
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @__kmpc_target_init(%struct.ident_t* @[[GLOB1:[0-9]+]], i1 false, i1 false, i1 true)
 ; CHECK-NEXT:    [[EXEC_USER_CODE:%.*]] = icmp eq i32 [[TMP0]], -1
 ; CHECK-NEXT:    br i1 [[EXEC_USER_CODE]], label [[USER_CODE_ENTRY:%.*]], label [[WORKER_EXIT:%.*]]
 ; CHECK:       user_code.entry:
-; CHECK-NEXT:    call void @__kmpc_target_deinit(%struct.ident_t* @[[GLOB1]], i1 true, i1 false)
+; CHECK-NEXT:    call void @__kmpc_target_deinit(%struct.ident_t* @[[GLOB1]], i1 false, i1 true)
 ; CHECK-NEXT:    ret void
 ; CHECK:       worker.exit:
 ; CHECK-NEXT:    ret void
 ;
 entry:
   %0 = call i32 @__kmpc_target_init(%struct.ident_t* @1, i1 false, i1 true, i1 true)
   %exec_user_code = icmp eq i32 %0, -1
   br i1 %exec_user_code, label %user_code.entry, label %worker.exit

llvm/test/Transforms/OpenMP/get_hardware_num_threads_in_block_fold.ll

;
   ret void
 }
 
 @kernel2_exec_mode = weak constant i8 1
 
 define weak void @kernel2() #0 {
 ; CHECK-LABEL: define {{[^@]+}}@kernel2
 ; CHECK-SAME: () #[[ATTR0]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CAPTURED_VARS_ADDRS:%.*]] = alloca [0 x i8*], align 8
 ; CHECK-NEXT:    [[I:%.*]] = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 true, i1 false, i1 false)
+; CHECK-NEXT:    [[EXEC_USER_CODE:%.*]] = icmp eq i32 [[I]], -1
+; CHECK-NEXT:    br i1 [[EXEC_USER_CODE]], label [[USER_CODE_ENTRY:%.*]], label [[COMMON_RET:%.*]]
+; CHECK:       common.ret:
+; CHECK-NEXT:    ret void
+; CHECK:       user_code.entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @__kmpc_global_thread_num(%struct.ident_t* null) #[[ATTR1]]
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast [0 x i8*]* [[CAPTURED_VARS_ADDRS]] to i8**
 ; CHECK-NEXT:    call void @helper0() #[[ATTR1]]
 ; CHECK-NEXT:    call void @helper1() #[[ATTR1]]
 ; CHECK-NEXT:    call void @helper2() #[[ATTR1]]
+; CHECK-NEXT:    call void @__kmpc_parallel_51(%struct.ident_t* null, i32 [[TMP0]], i32 1, i32 -1, i32 -1, i8* bitcast (void (i32*, i32*)* @__omp_outlined__ to i8*), i8* bitcast (void (i16, i32)* @__omp_outlined___wrapper to i8*), i8** [[TMP1]], i64 0)
 ; CHECK-NEXT:    call void @__kmpc_target_deinit(%struct.ident_t* null, i1 true, i1 false)
 ; CHECK-NEXT:    ret void
 ;
-  %i = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 false, i1 false, i1 false)
+entry:
+  %captured_vars_addrs = alloca [0 x i8*], align 8
+  %i = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 false, i1 true, i1 true)
+  %exec_user_code = icmp eq i32 %i, -1
+  br i1 %exec_user_code, label %user_code.entry, label %common.ret
+
+common.ret:
+  ret void
+
+user_code.entry:
+  %0 = call i32 @__kmpc_global_thread_num(%struct.ident_t* null)
+  %1 = bitcast [0 x i8*]* %captured_vars_addrs to i8**
   call void @helper0()
   call void @helper1()
   call void @helper2()
-  call void @__kmpc_target_deinit(%struct.ident_t* null, i1 false, i1 false)
+  call void @__kmpc_parallel_51(%struct.ident_t* null, i32 %0, i32 1, i32 -1, i32 -1, i8* bitcast (void (i32*, i32*)* @__omp_outlined__ to i8*), i8* bitcast (void (i16, i32)* @__omp_outlined___wrapper to i8*), i8** %1, i64 0)
+  call void @__kmpc_target_deinit(%struct.ident_t* null, i1 false, i1 true)
   ret void
 }
 
 define internal void @helper0() {
 ; CHECK-LABEL: define {{[^@]+}}@helper0
 ; CHECK-SAME: () #[[ATTR1]] {
 ; CHECK-NEXT:    br label [[REGION_CHECK_TID:%.*]]
 ; CHECK:       region.check.tid:

 ; CHECK:       region.exit:
 ; CHECK-NEXT:    ret void
 ;
   %threadLimit = call i32 @__kmpc_get_hardware_num_threads_in_block()
   store i32 %threadLimit, i32* @G
   ret void
 }
 
+define internal void @__omp_outlined__(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+; CHECK-LABEL: define {{[^@]+}}@__omp_outlined__
+; CHECK-SAME: (i32* noalias [[DOTGLOBAL_TID_:%.*]], i32* noalias [[DOTBOUND_TID_:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  ret void
+}
+
+define internal void @__omp_outlined___wrapper(i16 zeroext %0, i32 %1) {
+; CHECK-LABEL: define {{[^@]+}}@__omp_outlined___wrapper
+; CHECK-SAME: (i16 zeroext [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  ret void
+}
+
 declare i32 @__kmpc_get_hardware_num_threads_in_block()
 declare i32 @__kmpc_target_init(%struct.ident_t*, i1 zeroext, i1 zeroext, i1 zeroext) #1
 declare void @__kmpc_target_deinit(%struct.ident_t* nocapture readnone, i1 zeroext, i1 zeroext) #1
+declare void @__kmpc_parallel_51(%struct.ident_t*, i32, i32, i32, i32, i8*, i8*, i8**, i64)
+declare i32 @__kmpc_global_thread_num(%struct.ident_t*)
 
 
 !llvm.module.flags = !{!0, !1}
 !nvvm.annotations = !{!2, !3, !4}
 
 attributes #0 = { "omp_target_thread_limit"="666" "omp_target_num_teams"="777"}
 
 !0 = !{i32 7, !"openmp", i32 50}
 !1 = !{i32 7, !"openmp-device", i32 50}
 !2 = !{void ()* @kernel0, !"kernel", i32 1}
 !3 = !{void ()* @kernel1, !"kernel", i32 1}
 !4 = !{void ()* @kernel2, !"kernel", i32 1}
 ;
 ;.
 ; CHECK: attributes #[[ATTR0]] = { "omp_target_num_teams"="777" "omp_target_thread_limit"="666" }
 ; CHECK: attributes #[[ATTR1]] = { nounwind }
-; CHECK: attributes #[[ATTR2:[0-9]+]] = { convergent nounwind }
+; CHECK: attributes #[[ATTR2:[0-9]+]] = { alwaysinline }
+; CHECK: attributes #[[ATTR3:[0-9]+]] = { convergent nounwind }
 ;.
 ; CHECK: [[META0:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; CHECK: [[META1:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
 ; CHECK: [[META2:![0-9]+]] = !{void ()* @kernel0, !"kernel", i32 1}
 ; CHECK: [[META3:![0-9]+]] = !{void ()* @kernel1, !"kernel", i32 1}
 ; CHECK: [[META4:![0-9]+]] = !{void ()* @kernel2, !"kernel", i32 1}
 ;.

llvm/test/Transforms/OpenMP/is_spmd_exec_mode_fold.ll

;
   call void @is_spmd_helper2()
   call void @is_mixed_helper()
   call void @__kmpc_target_deinit(%struct.ident_t* null, i1 true, i1 false)
   ret void
 }
 
 define weak void @will_be_spmd() {
 ; CHECK-LABEL: define {{[^@]+}}@will_be_spmd() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CAPTURED_VARS_ADDRS:%.*]] = alloca [0 x i8*], align 8
 ; CHECK-NEXT:    [[I:%.*]] = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 true, i1 false, i1 false)
+; CHECK-NEXT:    [[EXEC_USER_CODE:%.*]] = icmp eq i32 [[I]], -1
+; CHECK-NEXT:    br i1 [[EXEC_USER_CODE]], label [[USER_CODE_ENTRY:%.*]], label [[COMMON_RET:%.*]]
+; CHECK:       common.ret:
+; CHECK-NEXT:    ret void
+; CHECK:       user_code.entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call i32 @__kmpc_global_thread_num(%struct.ident_t* null) #[[ATTR2:[0-9]+]]
+; CHECK-NEXT:    [[TMP1:%.*]] = bitcast [0 x i8*]* [[CAPTURED_VARS_ADDRS]] to i8**
 ; CHECK-NEXT:    call void @is_spmd_helper2()
+; CHECK-NEXT:    call void @__kmpc_parallel_51(%struct.ident_t* null, i32 [[TMP0]], i32 1, i32 -1, i32 -1, i8* bitcast (void (i32*, i32*)* @__omp_outlined__ to i8*), i8* bitcast (void (i16, i32)* @__omp_outlined___wrapper to i8*), i8** [[TMP1]], i64 0)
 ; CHECK-NEXT:    call void @__kmpc_target_deinit(%struct.ident_t* null, i1 true, i1 false)
 ; CHECK-NEXT:    ret void
 ;
-  %i = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 false, i1 false, i1 false)
+entry:
+  %captured_vars_addrs = alloca [0 x i8*], align 8
+  %i = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 false, i1 true, i1 true)
+  %exec_user_code = icmp eq i32 %i, -1
+  br i1 %exec_user_code, label %user_code.entry, label %common.ret
+
+common.ret:
+  ret void
+
+user_code.entry:
+  %0 = call i32 @__kmpc_global_thread_num(%struct.ident_t* null)
+  %1 = bitcast [0 x i8*]* %captured_vars_addrs to i8**
   call void @is_spmd_helper2()
-  call void @__kmpc_target_deinit(%struct.ident_t* null, i1 false, i1 false)
+  call void @__kmpc_parallel_51(%struct.ident_t* null, i32 %0, i32 1, i32 -1, i32 -1, i8* bitcast (void (i32*, i32*)* @__omp_outlined__ to i8*), i8* bitcast (void (i16, i32)* @__omp_outlined___wrapper to i8*), i8** %1, i64 0)
+  call void @__kmpc_target_deinit(%struct.ident_t* null, i1 false, i1 true)
   ret void
 }
 
 define weak void @non_spmd() {
 ; CHECK-LABEL: define {{[^@]+}}@non_spmd() {
 ; CHECK-NEXT:    [[I:%.*]] = call i32 @__kmpc_target_init(%struct.ident_t* null, i1 false, i1 false, i1 false)
 ; CHECK-NEXT:    call void @is_generic_helper1()
 ; CHECK-NEXT:    call void @is_generic_helper2()

 ; CHECK-NEXT:    store i8 [[ISSPMD]], i8* @G, align 1
 ; CHECK-NEXT:    ret void
 ;
   %isSPMD = call i8 @__kmpc_is_spmd_exec_mode()
   store i8 %isSPMD, i8* @G
   ret void
 }
 
+define internal void @__omp_outlined__(i32* noalias %.global_tid., i32* noalias %.bound_tid.) {
+; CHECK-LABEL: define {{[^@]+}}@__omp_outlined__
+; CHECK-SAME: (i32* noalias [[DOTGLOBAL_TID_:%.*]], i32* noalias [[DOTBOUND_TID_:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  ret void
+}
+
+define internal void @__omp_outlined___wrapper(i16 zeroext %0, i32 %1) {
+; CHECK-LABEL: define {{[^@]+}}@__omp_outlined___wrapper
+; CHECK-SAME: (i16 zeroext [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    ret void
+;
+entry:
+  ret void
+}
+
 declare void @spmd_compatible() "llvm.assume"="ompx_spmd_amenable"
 declare i8 @__kmpc_is_spmd_exec_mode()
-declare i32 @__kmpc_target_init(%struct.ident_t*, i1 zeroext, i1 zeroext, i1 zeroext) #1
-declare void @__kmpc_target_deinit(%struct.ident_t* nocapture readnone, i1 zeroext, i1 zeroext) #1
+declare i32 @__kmpc_target_init(%struct.ident_t*, i1 zeroext, i1 zeroext, i1 zeroext)
+declare void @__kmpc_target_deinit(%struct.ident_t* nocapture readnone, i1 zeroext, i1 zeroext)
+declare void @__kmpc_parallel_51(%struct.ident_t*, i32, i32, i32, i32, i8*, i8*, i8**, i64)
+declare i32 @__kmpc_global_thread_num(%struct.ident_t*)
 declare void @foo()
 declare void @bar()
 
 !llvm.module.flags = !{!0, !1}
 !nvvm.annotations = !{!2, !3, !4, !5}
 
 !0 = !{i32 7, !"openmp", i32 50}
 !1 = !{i32 7, !"openmp-device", i32 50}
 !2 = !{void ()* @is_spmd, !"kernel", i32 1}
 !3 = !{void ()* @will_be_spmd, !"kernel", i32 1}
 !4 = !{void ()* @non_spmd, !"kernel", i32 1}
 !5 = !{void ()* @will_not_be_spmd, !"kernel", i32 1}
 ;.
 ; CHECK: attributes #[[ATTR0:[0-9]+]] = { "llvm.assume"="ompx_spmd_amenable" }
+; CHECK: attributes #[[ATTR1:[0-9]+]] = { alwaysinline }
+; CHECK: attributes #[[ATTR2]] = { nounwind }
 ;.
 ; CHECK: [[META0:![0-9]+]] = !{i32 7, !"openmp", i32 50}
 ; CHECK: [[META1:![0-9]+]] = !{i32 7, !"openmp-device", i32 50}
 ; CHECK: [[META2:![0-9]+]] = !{void ()* @is_spmd, !"kernel", i32 1}
 ; CHECK: [[META3:![0-9]+]] = !{void ()* @will_be_spmd, !"kernel", i32 1}
 ; CHECK: [[META4:![0-9]+]] = !{void ()* @non_spmd, !"kernel", i32 1}
 ; CHECK: [[META5:![0-9]+]] = !{void ()* @will_not_be_spmd, !"kernel", i32 1}
 ;.