[flang][cuda] Allow to set the stack limit size

flang/CMakeLists.txt

@@ -471,6 +471,13 @@ if (FLANG_INCLUDE_TESTS)
   add_compile_definitions(FLANG_INCLUDE_TESTS=1)
 endif()
 
+option(FLANG_CUF_RUNTIME
+  "Compile CUDA Fortran runtime sources" OFF)
+if (FLANG_CUF_RUNTIME)
+  find_package(CUDAToolkit REQUIRED)
+  add_compile_definitions(FLANG_CUDA_SUPPORT=1)
+endif()
+
 add_subdirectory(include)
 add_subdirectory(lib)
 add_subdirectory(cmake/modules)
@@ -481,12 +488,6 @@ if (FLANG_BUILD_TOOLS)
   add_subdirectory(tools)
 endif()
 
-option(FLANG_CUF_RUNTIME
-  "Compile CUDA Fortran runtime sources" OFF)
-if (FLANG_CUF_RUNTIME)
-  find_package(CUDAToolkit REQUIRED)
-endif()
-
 add_subdirectory(runtime)
 
 if (LLVM_INCLUDE_EXAMPLES)

flang/include/flang/Optimizer/Builder/Runtime/Main.h

@@ -24,7 +24,8 @@ class GlobalOp;
 namespace fir::runtime {
 
 void genMain(fir::FirOpBuilder &builder, mlir::Location loc,
-             const std::vector<Fortran::lower::EnvironmentDefault> &defs);
+             const std::vector<Fortran::lower::EnvironmentDefault> &defs,
+             bool initCuda = false);
 }
 
 #endif // FORTRAN_OPTIMIZER_BUILDER_RUNTIME_MAIN_H

flang/include/flang/Runtime/CUDA/init.h

@@ -0,0 +1,20 @@
+//===-- include/flang/Runtime/CUDA/init.h -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_RUNTIME_CUDA_INIT_H_
+#define FORTRAN_RUNTIME_CUDA_INIT_H_
+
+#include "common.h"
+#include "flang/Runtime/entry-names.h"
+
+extern "C" {
+
+void RTDECL(CUFInit)();
+}
+
+#endif // FORTRAN_RUNTIME_CUDA_INIT_H_

flang/lib/Lower/Bridge.cpp

@@ -459,7 +459,9 @@ class FirConverter : public Fortran::lower::AbstractConverter {
     if (hasMainProgram)
       createGlobalOutsideOfFunctionLowering([&]() {
         fir::runtime::genMain(*builder, toLocation(),
-                              bridge.getEnvironmentDefaults());
+                              bridge.getEnvironmentDefaults(),
+                              getFoldingContext().languageFeatures().IsEnabled(
+                                  Fortran::common::LanguageFeature::CUDA));
       });
 
     finalizeOpenACCLowering();

flang/lib/Optimizer/Builder/Runtime/Main.cpp

@@ -16,13 +16,17 @@
 #include "flang/Optimizer/Dialect/FIRType.h"
 #include "flang/Runtime/main.h"
 #include "flang/Runtime/stop.h"
+#ifdef FLANG_CUDA_SUPPORT
+#include "flang/Runtime/CUDA/init.h"
+#endif
 
 using namespace Fortran::runtime;
 
 /// Create a `int main(...)` that calls the Fortran entry point
 void fir::runtime::genMain(
     fir::FirOpBuilder &builder, mlir::Location loc,
-    const std::vector<Fortran::lower::EnvironmentDefault> &defs) {
+    const std::vector<Fortran::lower::EnvironmentDefault> &defs,
+    bool initCuda) {
   auto *context = builder.getContext();
   auto argcTy = builder.getDefaultIntegerType();
   auto ptrTy = mlir::LLVM::LLVMPointerType::get(context);
@@ -61,6 +65,15 @@ void fir::runtime::genMain(
   args.push_back(env);
 
   builder.create<fir::CallOp>(loc, startFn, args);
+
+#ifdef FLANG_CUDA_SUPPORT
+  if (initCuda) {
+    auto initFn = builder.createFunction(
+        loc, RTNAME_STRING(CUFInit), mlir::FunctionType::get(context, {}, {}));
+    builder.create<fir::CallOp>(loc, initFn);
+  }
+#endif
+
   builder.create<fir::CallOp>(loc, qqMainFn);
   builder.create<fir::CallOp>(loc, stopFn);
 

flang/runtime/CUDA/CMakeLists.txt

@@ -17,6 +17,7 @@ add_flang_library(${CUFRT_LIBNAME}
   allocator.cpp
   allocatable.cpp
   descriptor.cpp
+  init.cpp
   kernel.cpp
   memmove-function.cpp
   memory.cpp

flang/runtime/CUDA/init.cpp

@@ -0,0 +1,25 @@
+//===-- runtime/CUDA/init.cpp ---------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "flang/Runtime/CUDA/init.h"
+#include "../environment.h"
+#include "../terminator.h"
+#include "flang/Runtime/CUDA/common.h"
+
+#include "cuda_runtime.h"
+
+extern "C" {
+
+void RTDEF(CUFInit)() {
+  // Perform ctx initialization based on execution environment if necessary.
+  if (Fortran::runtime::executionEnvironment.cudaStackLimit) {
+    CUDA_REPORT_IF_ERROR(cudaDeviceSetLimit(cudaLimitStackSize,
+        Fortran::runtime::executionEnvironment.cudaStackLimit));
+  }
+}
+}

flang/runtime/environment.cpp

@@ -143,6 +143,18 @@ void ExecutionEnvironment::Configure(int ac, const char *av[],
     }
   }
 
+  if (auto *x{std::getenv("ACC_OFFLOAD_STACK_SIZE")}) {
+    char *end;
+    auto n{std::strtoul(x, &end, 10)};
+    if (n > 0 && n < std::numeric_limits<std::size_t>::max() && *end == '\0') {
+      cudaStackLimit = n;
+    } else {
+      std::fprintf(stderr,
+          "Fortran runtime: ACC_OFFLOAD_STACK_SIZE=%s is invalid; ignored\n",
+          x);
+    }
+  }
+
   // TODO: Set RP/ROUND='PROCESSOR_DEFINED' from environment
 }
 

flang/runtime/environment.h

@@ -56,6 +56,9 @@ struct ExecutionEnvironment {
   bool noStopMessage{false}; // NO_STOP_MESSAGE=1 inhibits "Fortran STOP"
   bool defaultUTF8{false}; // DEFAULT_UTF8
   bool checkPointerDeallocation{true}; // FORT_CHECK_POINTER_DEALLOCATION
+
+  // CUDA related variables
+  std::size_t cudaStackLimit{0}; // ACC_OFFLOAD_STACK_SIZE
 };
 
 RT_OFFLOAD_VAR_GROUP_BEGIN