[llvm] [Offload] Add `--kernel <name>` command to `llvm-gpu-loader` (PR #213738)

[Nick Sarnie via llvm-commits]

================
@@ -263,21 +273,31 @@ int main(int argc, const char **argv, const char **envp) {
   OFFLOAD_ERR(olMemAlloc(Device, OL_ALLOC_TYPE_DEVICE, sizeof(int), &DevRet));
   OFFLOAD_ERR(olMemcpy(Queue, DevRet, Device, &Zero, Host, sizeof(int)));
 
+  // The '_begin' and '_end' kernels perform libc startup and teardown. Global
+  // constructors and destructors are handled automatically by the runtime.
   ol_kernel_launch_size_args_t BeginLaunch{1, {1, 1, 1}, {1, 1, 1}, 0};
-  launchKernel(Queue, Device, Program, "_begin", BeginLaunch, DevArgc, DevArgv,
-               DevEnvp);
+  if (hasKernel(Program, "_begin"))
+    launchKernel(Queue, Device, Program, "_begin", BeginLaunch, DevArgc,
+                 DevArgv, DevEnvp);
   OFFLOAD_ERR(olSyncQueue(Queue));
 
   uint32_t Dims = (BlocksZ > 1) ? 3 : (BlocksY > 1) ? 2 : 1;
   ol_kernel_launch_size_args_t StartLaunch{Dims,
                                            {BlocksX, BlocksY, BlocksZ},
                                            {ThreadsX, ThreadsY, ThreadsZ},
                                            /*SharedMemBytes=*/0};
-  launchKernel(Queue, Device, Program, "_start", StartLaunch, DevArgc, DevArgv,
-               DevEnvp, DevRet);
+  if (Kernels.empty()) {
+    launchKernel(Queue, Device, Program, "_start", StartLaunch, DevArgc,
+                 DevArgv, DevEnvp, DevRet);
+  } else {
+    // Launch the user-specified kernels in order. These must take no arguments.
+    for (const std::string &Kernel : Kernels)
+      launchKernel(Queue, Device, Program, Kernel.c_str(), StartLaunch);
+  }
 
   ol_kernel_launch_size_args_t EndLaunch{1, {1, 1, 1}, {1, 1, 1}, 0};
-  launchKernel(Queue, Device, Program, "_end", EndLaunch);
+  if (hasKernel(Program, "_end"))
+    launchKernel(Queue, Device, Program, "_end", EndLaunch);
 
   int Ret;
----------------
sarnex wrote:

cool thanks

https://github.com/llvm/llvm-project/pull/213738