mlir/lib/Dialect/GPU/Transforms: improve context management in SerializeToCubin

This commit adjusts the CUDA context management in the SerializeToCubin pass.
In particular, it uses the device 0 primary context instead of creating a new
CUDA context on each invocation of SerializeToCubin. This yields very large
improvements in compile time, especially if an application (like a JIT compiler)
is calling SerializeToCubin repeatedly.

Differential Revision: https://reviews.llvm.org/D159487

Author: Rohan Yadav

mlir/lib/Dialect/GPU/Transforms/SerializeToCubin.cpp

@@ -110,7 +110,11 @@ SerializeToCubinPass::serializeISA(const std::string &isa) {
   CUdevice device;
   RETURN_ON_CUDA_ERROR(cuDeviceGet(&device, 0));
   CUcontext context;
-  RETURN_ON_CUDA_ERROR(cuCtxCreate(&context, 0, device));
+  // Use the primary context.
+  RETURN_ON_CUDA_ERROR(cuDevicePrimaryCtxRetain(&context, device));
+  // Push the primary context so that the next CUDA operations
+  // actually use it.
+  RETURN_ON_CUDA_ERROR(cuCtxPushCurrent(context));
   CUlinkState linkState;
 
   CUjit_option jitOptions[] = {CU_JIT_ERROR_LOG_BUFFER,
@@ -146,7 +150,10 @@ SerializeToCubinPass::serializeISA(const std::string &isa) {
 
   // This will also destroy the cubin data.
   RETURN_ON_CUDA_ERROR(cuLinkDestroy(linkState));
-  RETURN_ON_CUDA_ERROR(cuCtxDestroy(context));
+  // Pop and release the primary context.
+  CUcontext poppedContext;
+  RETURN_ON_CUDA_ERROR(cuCtxPopCurrent(&poppedContext));
+  RETURN_ON_CUDA_ERROR(cuDevicePrimaryCtxRelease(device));
 
   return result;
 }