[Offload] Fix handling of 'bare' mode when environment missing (llvm#136794)

Summary:
We treated the missing kernel environment as a unique mode, but it was
kind of this random bool that was doing the same thing and it explicitly
expects the kernel environment to be zero. It broke after the previous
change since it used to default to SPMD and didn't handle zero in any of
the other cases despite being used. This fixes that and queries for it
without needing to consume an error.

Author: jhuber6

llvm/include/llvm/Frontend/OpenMP/OMPDeviceConstants.h

@@ -19,6 +19,7 @@ namespace llvm {
 namespace omp {
 
 enum OMPTgtExecModeFlags : unsigned char {
+  OMP_TGT_EXEC_MODE_BARE = 0,
   OMP_TGT_EXEC_MODE_GENERIC = 1 << 0,
   OMP_TGT_EXEC_MODE_SPMD = 1 << 1,
   OMP_TGT_EXEC_MODE_GENERIC_SPMD =

offload/DeviceRTL/src/Kernel.cpp

@@ -26,6 +26,7 @@ using namespace ompx;
 // These flags are copied from "llvm/Frontend/OpenMP/OMPDeviceConstants.h" and
 // must be kept in-sync.
 enum OMPTgtExecModeFlags : unsigned char {
+  OMP_TGT_EXEC_MODE_BARE = 0,
   OMP_TGT_EXEC_MODE_GENERIC = 1 << 0,
   OMP_TGT_EXEC_MODE_SPMD = 1 << 1,
   OMP_TGT_EXEC_MODE_GENERIC_SPMD =

offload/plugins-nextgen/common/include/PluginInterface.h

@@ -297,6 +297,7 @@ struct GenericKernelTy {
   /// Indicate whether an execution mode is valid.
   static bool isValidExecutionMode(OMPTgtExecModeFlags ExecutionMode) {
     switch (ExecutionMode) {
+    case OMP_TGT_EXEC_MODE_BARE:
     case OMP_TGT_EXEC_MODE_SPMD:
     case OMP_TGT_EXEC_MODE_GENERIC:
     case OMP_TGT_EXEC_MODE_GENERIC_SPMD:
@@ -309,6 +310,8 @@ struct GenericKernelTy {
   /// Get the execution mode name of the kernel.
   const char *getExecutionModeName() const {
     switch (KernelEnvironment.Configuration.ExecMode) {
+    case OMP_TGT_EXEC_MODE_BARE:
+      return "BARE";
     case OMP_TGT_EXEC_MODE_SPMD:
       return "SPMD";
     case OMP_TGT_EXEC_MODE_GENERIC:
@@ -364,6 +367,9 @@ struct GenericKernelTy {
   bool isSPMDMode() const {
     return KernelEnvironment.Configuration.ExecMode == OMP_TGT_EXEC_MODE_SPMD;
   }
+  bool isBareMode() const {
+    return KernelEnvironment.Configuration.ExecMode == OMP_TGT_EXEC_MODE_BARE;
+  }
 
   /// The kernel name.
   const char *Name;

offload/plugins-nextgen/common/src/PluginInterface.cpp

@@ -440,18 +440,19 @@ Error GenericKernelTy::init(GenericDeviceTy &GenericDevice,
   ImagePtr = &Image;
 
   // Retrieve kernel environment object for the kernel.
-  GlobalTy KernelEnv(std::string(Name) + "_kernel_environment",
-                     sizeof(KernelEnvironment), &KernelEnvironment);
+  std::string EnvironmentName = std::string(Name) + "_kernel_environment";
   GenericGlobalHandlerTy &GHandler = GenericDevice.Plugin.getGlobalHandler();
-  if (auto Err =
-          GHandler.readGlobalFromImage(GenericDevice, *ImagePtr, KernelEnv)) {
-    [[maybe_unused]] std::string ErrStr = toString(std::move(Err));
-    DP("Failed to read kernel environment for '%s': %s\n"
-       "Using default SPMD (2) execution mode\n",
-       Name, ErrStr.data());
-    assert(KernelEnvironment.Configuration.ReductionDataSize == 0 &&
-           "Default initialization failed.");
-    IsBareKernel = true;
+  if (GHandler.isSymbolInImage(GenericDevice, Image, EnvironmentName)) {
+    GlobalTy KernelEnv(EnvironmentName, sizeof(KernelEnvironment),
+                       &KernelEnvironment);
+    if (auto Err =
+            GHandler.readGlobalFromImage(GenericDevice, *ImagePtr, KernelEnv))
+      return Err;
+  } else {
+    KernelEnvironment = KernelEnvironmentTy{};
+    DP("Failed to read kernel environment for '%s' Using default Bare (0) "
+       "execution mode\n",
+       Name);
   }
 
   // Max = Config.Max > 0 ? min(Config.Max, Device.Max) : Device.Max;
@@ -573,7 +574,7 @@ Error GenericKernelTy::launch(GenericDeviceTy &GenericDevice, void **ArgPtrs,
                             KernelArgs.ThreadLimit[2]};
   uint32_t NumBlocks[3] = {KernelArgs.NumTeams[0], KernelArgs.NumTeams[1],
                            KernelArgs.NumTeams[2]};
-  if (!IsBareKernel) {
+  if (!isBareMode()) {
     NumThreads[0] = getNumThreads(GenericDevice, NumThreads);
     NumBlocks[0] = getNumBlocks(GenericDevice, NumBlocks, KernelArgs.Tripcount,
                                 NumThreads[0], KernelArgs.ThreadLimit[0] > 0);
@@ -627,7 +628,7 @@ KernelLaunchParamsTy GenericKernelTy::prepareArgs(
 
 uint32_t GenericKernelTy::getNumThreads(GenericDeviceTy &GenericDevice,
                                         uint32_t ThreadLimitClause[3]) const {
-  assert(!IsBareKernel && "bare kernel should not call this function");
+  assert(!isBareMode() && "bare kernel should not call this function");
 
   assert(ThreadLimitClause[1] == 1 && ThreadLimitClause[2] == 1 &&
          "Multi dimensional launch not supported yet.");
@@ -645,7 +646,7 @@ uint32_t GenericKernelTy::getNumBlocks(GenericDeviceTy &GenericDevice,
                                        uint64_t LoopTripCount,
                                        uint32_t &NumThreads,
                                        bool IsNumThreadsFromUser) const {
-  assert(!IsBareKernel && "bare kernel should not call this function");
+  assert(!isBareMode() && "bare kernel should not call this function");
 
   assert(NumTeamsClause[1] == 1 && NumTeamsClause[2] == 1 &&
          "Multi dimensional launch not supported yet.");

offload/test/offloading/ompx_bare.c

@@ -15,7 +15,7 @@ int main(int argc, char *argv[]) {
   const int N = num_blocks * block_size;
   int *data = (int *)malloc(N * sizeof(int));
 
-  // CHECK: "PluginInterface" device 0 info: Launching kernel __omp_offloading_{{.*}} with [64,1,1] blocks and [64,1,1] threads in SPMD mode
+  // CHECK: "PluginInterface" device 0 info: Launching kernel __omp_offloading_{{.*}} with [64,1,1] blocks and [64,1,1] threads in BARE mode
 
 #pragma omp target teams ompx_bare num_teams(num_blocks) thread_limit(block_size) map(from: data[0:N])
   {

offload/test/offloading/ompx_bare_multi_dim.cpp

@@ -7,7 +7,7 @@
 #include <cassert>
 #include <vector>
 
-// CHECK: "PluginInterface" device 0 info: Launching kernel __omp_offloading_{{.*}} with [2,4,6] blocks and [32,4,2] threads in SPMD mode
+// CHECK: "PluginInterface" device 0 info: Launching kernel __omp_offloading_{{.*}} with [2,4,6] blocks and [32,4,2] threads in BARE mode
 
 int main(int argc, char *argv[]) {
   int bs[3] = {32u, 4u, 2u};