[llvm] [offload][omp] Move reading _kernel_environment to libomptarget (PR #222606)

[Joseph Huber via llvm-commits]

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@@ -461,6 +466,67 @@ static int loadImagesOntoDevice(DeviceTy &Device) {
           if (Device.RTL->get_function(Binary, Entry.SymbolName,
                                        &DeviceEntry.Address) != OFFLOAD_SUCCESS)
             REPORT() << "Failed to load kernel " << Entry.SymbolName;
+
+          // Read this kernel's launch-geometry properties once, from its
+          // "<name>_kernel_environment" device global, and cache them on
+          // the device for use at launch time.
+          std::string EnvName =
+              std::string(Entry.SymbolName) + "_kernel_environment";
+          KernelEnvironmentTy KernelEnv{};
+          void *KernelEnvPtr = nullptr;
+          bool ReadOk =
+              Device.RTL->get_global(Binary, sizeof(KernelEnv), EnvName.c_str(),
+                                     &KernelEnvPtr) == OFFLOAD_SUCCESS &&
+              Device.RTL->data_retrieve(DeviceId, &KernelEnv, KernelEnvPtr,
+                                        sizeof(KernelEnv)) == OFFLOAD_SUCCESS;
+          if (!ReadOk) {
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jhuber6 wrote:

I actually wonder if we should keep this fallback, it was initially intended to drive the non-OpenMP cases but if it's in `libomptarget` we could just consider this an ABI violation. I'd probably prefer that unless someone can think of a case where OpenMP wouldn't generate this for one of the kernels it creates / registers.

https://github.com/llvm/llvm-project/pull/222606