[flang][cuda] Implicitly load cudadevice module in device/global subprogram

[clementval]

Some functions and subroutines are available in device context (device/global). These functions have interfaces declared in the cudadevice module.

This patch adds interfaces as __cuda_device_builtins_<fctname> in a builtin module and they are USE'd rename in the cudadevice module. The module is implicitly used in device/global subprograms.

The builtin module only contains procedures from section 3.6.4 for now.

[llvmbot]

@llvm/pr-subscribers-flang-semantics

Author: Valentin Clement (バレンタイン クレメン) (clementval)

Changes

Some functions and subroutines are available in device context (device/global). These functions have interfaces declared in the cudadevice module.

This patch adds interfaces as __cuda_device_builtins_<fctname> in a builtin module and they are USE'd rename in the cudadevice module. The module is implicitly used in device/global subprograms.

The builtin module only contains procedures from section 3.6.4 for now.

---

Full diff: https://github.com/llvm/llvm-project/pull/91668.diff

8 Files Affected:

• (modified) flang/include/flang/Semantics/semantics.h (+4-1)
• (modified) flang/lib/Semantics/check-cuda.cpp (+4)
• (modified) flang/lib/Semantics/resolve-names.cpp (+11)
• (modified) flang/lib/Semantics/semantics.cpp (+8)
• (added) flang/module/__cuda_device_builtins.f90 (+74)
• (added) flang/module/cudadevice.f90 (+21)
• (added) flang/test/Semantics/cuf-device-procedures.cuf (+35)
• (modified) flang/tools/f18/CMakeLists.txt (+2)

diff --git a/flang/include/flang/Semantics/semantics.h b/flang/include/flang/Semantics/semantics.h
index e6ba71d53e92b..367c9224df974 100644
--- a/flang/include/flang/Semantics/semantics.h
+++ b/flang/include/flang/Semantics/semantics.h
@@ -214,9 +214,11 @@ class SemanticsContext {
   // Defines builtinsScope_ from the __Fortran_builtins module
   void UseFortranBuiltinsModule();
   const Scope *GetBuiltinsScope() const { return builtinsScope_; }
+  
+  const Scope &GetCUDABuiltinsScope();
+  const Scope &GetCUDADeviceScope();
 
   void UsePPCBuiltinTypesModule();
-  const Scope &GetCUDABuiltinsScope();
   void UsePPCBuiltinsModule();
   Scope *GetPPCBuiltinTypesScope() { return ppcBuiltinTypesScope_; }
   const Scope *GetPPCBuiltinsScope() const { return ppcBuiltinsScope_; }
@@ -292,6 +294,7 @@ class SemanticsContext {
   const Scope *builtinsScope_{nullptr}; // module __Fortran_builtins
   Scope *ppcBuiltinTypesScope_{nullptr}; // module __Fortran_PPC_types
   std::optional<const Scope *> cudaBuiltinsScope_; // module __CUDA_builtins
+  std::optional<const Scope *> cudaDeviceScope_; // module cudadevice
   const Scope *ppcBuiltinsScope_{nullptr}; // module __ppc_intrinsics
   std::list<parser::Program> modFileParseTrees_;
   std::unique_ptr<CommonBlockMap> commonBlockMap_;
diff --git a/flang/lib/Semantics/check-cuda.cpp b/flang/lib/Semantics/check-cuda.cpp
index 96ab902392633..6c32db4dbd1b3 100644
--- a/flang/lib/Semantics/check-cuda.cpp
+++ b/flang/lib/Semantics/check-cuda.cpp
@@ -82,6 +82,10 @@ struct DeviceExprChecker
           }
         }
       }
+      if (sym->owner().IsModule() &&
+          DEREF(sym->owner().symbol()).name() == "__cuda_device_builtins") {
+        return {};
+      }
     } else if (x.GetSpecificIntrinsic()) {
       // TODO(CUDA): Check for unsupported intrinsics here
       return {};
diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
index 61394b0f41de7..16c555ff668aa 100644
--- a/flang/lib/Semantics/resolve-names.cpp
+++ b/flang/lib/Semantics/resolve-names.cpp
@@ -3797,6 +3797,17 @@ bool SubprogramVisitor::Pre(const parser::PrefixSpec::Attributes &attrs) {
         subp->set_cudaSubprogramAttrs(attr);
       }
     }
+    if (auto attrs{subp->cudaSubprogramAttrs()}) {
+      if (*attrs == common::CUDASubprogramAttrs::Global ||
+          *attrs == common::CUDASubprogramAttrs::Device) {
+        // Implicitly USE the cudadevice module by copying its symbol in the
+        // current scope.
+        const Scope &scope{context().GetCUDADeviceScope()};
+        for (auto sym : scope.GetSymbols()) {
+          currScope().CopySymbol(sym);
+        }
+      }
+    }
   }
   return false;
 }
diff --git a/flang/lib/Semantics/semantics.cpp b/flang/lib/Semantics/semantics.cpp
index 6ccd915c4dcbf..d51cc62d804e8 100644
--- a/flang/lib/Semantics/semantics.cpp
+++ b/flang/lib/Semantics/semantics.cpp
@@ -543,6 +543,14 @@ const Scope &SemanticsContext::GetCUDABuiltinsScope() {
   return **cudaBuiltinsScope_;
 }
 
+const Scope &SemanticsContext::GetCUDADeviceScope() {
+  if (!cudaDeviceScope_) {
+    cudaDeviceScope_ = GetBuiltinModule("cudadevice");
+    CHECK(cudaDeviceScope_.value() != nullptr);
+  }
+  return **cudaDeviceScope_;
+}
+
 void SemanticsContext::UsePPCBuiltinsModule() {
   if (ppcBuiltinsScope_ == nullptr) {
     ppcBuiltinsScope_ = GetBuiltinModule("__ppc_intrinsics");
diff --git a/flang/module/__cuda_device_builtins.f90 b/flang/module/__cuda_device_builtins.f90
new file mode 100644
index 0000000000000..738dc97242f2b
--- /dev/null
+++ b/flang/module/__cuda_device_builtins.f90
@@ -0,0 +1,74 @@
+!===-- module/__cuda_device_builtins.f90 -----------------------------------===!
+!
+! 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
+!
+!===------------------------------------------------------------------------===!
+
+! CUDA Fortran procedures available in device subprogram
+
+module __CUDA_device_builtins  
+
+  implicit none
+
+  ! Set PRIVATE by default to explicitly only export what is meant
+  ! to be exported by this MODULE.
+  private
+
+  ! Synchronization Functions
+
+  interface
+    subroutine __cuda_device_builtins_syncthreads()
+    end subroutine
+  end interface
+  public :: __cuda_device_builtins_syncthreads
+
+  interface
+    integer function __cuda_device_builtins_syncthreads_and(value)
+      integer :: value
+    end function
+  end interface
+  public :: __cuda_device_builtins_syncthreads_and
+
+  interface
+    integer function __cuda_device_builtins_syncthreads_count(value)
+      integer :: value
+    end function
+  end interface
+  public :: __cuda_device_builtins_syncthreads_count
+
+  interface
+    integer function __cuda_device_builtins_syncthreads_or(int_value)
+    end function
+  end interface
+  public :: __cuda_device_builtins_syncthreads_or
+
+  interface
+    subroutine __cuda_device_builtins_syncwarp(mask)
+      integer :: mask
+    end subroutine
+  end interface
+  public :: __cuda_device_builtins_syncwarp
+
+  ! Memory Fences
+
+  interface
+    subroutine __cuda_device_builtins_threadfence()
+    end subroutine
+  end interface
+  public :: __cuda_device_builtins_threadfence
+
+  interface
+    subroutine __cuda_device_builtins_threadfence_block()
+    end subroutine
+  end interface
+  public :: __cuda_device_builtins_threadfence_block
+
+  interface
+    subroutine __cuda_device_builtins_threadfence_system()
+    end subroutine
+  end interface
+  public :: __cuda_device_builtins_threadfence_system
+
+end module
diff --git a/flang/module/cudadevice.f90 b/flang/module/cudadevice.f90
new file mode 100644
index 0000000000000..b635d77ea4529
--- /dev/null
+++ b/flang/module/cudadevice.f90
@@ -0,0 +1,21 @@
+!===-- module/cudedevice.f90 -----------------------------------------------===!
+!
+! 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
+!
+!===------------------------------------------------------------------------===!
+
+! CUDA Fortran procedures available in device subprogram
+
+module cudadevice
+  use __cuda_device_builtins, only: &
+    syncthreads => __cuda_device_builtins_syncthreads, &
+    syncthreads_and => __cuda_device_builtins_syncthreads_and, &
+    syncthreads_count => __cuda_device_builtins_syncthreads_count, &
+    syncthreads_or => __cuda_device_builtins_syncthreads_or, &
+    syncwarp => __cuda_device_builtins_syncwarp, &
+    threadfence => __cuda_device_builtins_threadfence, &
+    threadfence_block => __cuda_device_builtins_threadfence_block, &
+    threadfence_system => __cuda_device_builtins_threadfence_system
+end module
diff --git a/flang/test/Semantics/cuf-device-procedures.cuf b/flang/test/Semantics/cuf-device-procedures.cuf
new file mode 100644
index 0000000000000..e79423e3587a1
--- /dev/null
+++ b/flang/test/Semantics/cuf-device-procedures.cuf
@@ -0,0 +1,35 @@
+! RUN: %flang_fc1 -fdebug-dump-symbols %s | FileCheck %s
+
+! Test CUDA Fortran intrinsic can pass semantic
+
+attributes(global) subroutine devsub()
+  implicit none
+  integer :: ret
+
+  ! 3.6.4. Synchronization Functions
+  call syncthreads()
+  call syncwarp(1)
+  call threadfence()
+  call threadfence_block()
+  call threadfence_system()
+  ret = syncthreads_and(1)
+  ret = syncthreads_count(1)
+  ret = syncthreads_or(1)
+end
+
+! CHECK-LABEL: Subprogram scope: devsub
+! CHECK: syncthreads, EXTERNAL, PUBLIC (Subroutine): Use from __cuda_device_builtins_syncthreads in __cuda_device_builtins
+! CHECK: syncthreads_and, EXTERNAL, PUBLIC (Function): Use from __cuda_device_builtins_syncthreads_and in __cuda_device_builtins
+! CHECK: syncthreads_count, EXTERNAL, PUBLIC (Function): Use from __cuda_device_builtins_syncthreads_count in __cuda_device_builtins
+! CHECK: syncthreads_or, EXTERNAL, PUBLIC (Function): Use from __cuda_device_builtins_syncthreads_or in __cuda_device_builtins
+! CHECK: syncwarp, EXTERNAL, PUBLIC (Subroutine): Use from __cuda_device_builtins_syncwarp in __cuda_device_builtins
+! CHECK: threadfence, EXTERNAL, PUBLIC (Subroutine): Use from __cuda_device_builtins_threadfence in __cuda_device_builtins
+! CHECK: threadfence_block, EXTERNAL, PUBLIC (Subroutine): Use from __cuda_device_builtins_threadfence_block in __cuda_device_builtins
+! CHECK: threadfence_system, EXTERNAL, PUBLIC (Subroutine): Use from __cuda_device_builtins_threadfence_system in __cuda_device_builtins
+
+subroutine host()
+  call syncthreads()
+end subroutine
+
+! CHECK-LABEL: Subprogram scope: host
+! CHECK: syncthreads, EXTERNAL: HostAssoc{{$}}
diff --git a/flang/tools/f18/CMakeLists.txt b/flang/tools/f18/CMakeLists.txt
index 64815a1f5da62..e5cf945d1f118 100644
--- a/flang/tools/f18/CMakeLists.txt
+++ b/flang/tools/f18/CMakeLists.txt
@@ -12,6 +12,8 @@ set(MODULES
   "__ppc_intrinsics"
   "mma"
   "__cuda_builtins"
+  "__cuda_device_builtins"
+  "cudadevice"
   "ieee_arithmetic"
   "ieee_exceptions"
   "ieee_features"

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[klausler]

s/symbol/symbols/

What about clashes with names that are already in scope (or declared later)?

[clementval]

So according to the reference compiler we should not overwrite what is already in scope so I updated the copy of symbol and added a test.
For what is declared after, in device or global procedure, we will have an error msg. I added a test also for this case.

[klausler]

So the semantics of these names are not really what you get from either a USE statement or from intrinsics.

There is already precedence here with names like threadIdx that are automatically imported into device subprogram scopes, so I guess this isn't making things any worse.

[klausler]

So the semantics of these names are not really what you get from either a USE statement or from intrinsics.

There is already precedence here with names like threadIdx that are automatically imported into device subprogram scopes, so I guess this isn't making things any worse.

[klausler]

These could all be in __fortran_builtins, which already contains some built-in CUDA definitions.

[clementval]

The reason I added a new file is that we can check on the module name instead of having to check on the module name and the procedure prefix.
I can moved them in __fortran_builtins but we would need to check if the procedure names starts with __cuda_device_builtins_ as well.