[clang] [llvm] [CUDA][HIP] warn incompatible redeclare (PR #77359)

[Yaxun Liu via llvm-commits]

https://github.com/yxsamliu updated https://github.com/llvm/llvm-project/pull/77359

>From dd589653a94faba3a458134b5713a82886271c86 Mon Sep 17 00:00:00 2001
From: "Yaxun (Sam) Liu" <yaxun.liu at amd.com>
Date: Thu, 30 May 2024 16:02:37 -0400
Subject: [PATCH] [CUDA][HIP] warn incompatible redeclare

nvcc warns about the following code:

but clang does not since clang allows device function to
overload host function.

Users want clang to emit similar warning to help code to be
compatible with nvcc.

Since this may cause regression with existing code, the warning
is off by default and can be enabled by -Woffload-incompatible-redeclare.

It won't cause warning in system headers, even with
-Woffload-incompatible-redeclare.
---
 .../clang/Basic/DiagnosticSemaKinds.td        |  5 +++
 clang/lib/Sema/SemaCUDA.cpp                   | 41 +++++++++++--------
 clang/test/SemaCUDA/function-redclare.cu      | 19 +++++++++
 llvm/docs/CompileCudaWithLLVM.rst             | 11 +++++
 4 files changed, 60 insertions(+), 16 deletions(-)
 create mode 100644 clang/test/SemaCUDA/function-redclare.cu

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 9f0b6f5a36389..2394ef7de6494 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -9013,6 +9013,11 @@ def err_cuda_ovl_target : Error<
   "cannot overload %select{__device__|__global__|__host__|__host__ __device__}2 function %3">;
 def note_cuda_ovl_candidate_target_mismatch : Note<
     "candidate template ignored: target attributes do not match">;
+def warn_offload_incompatible_redeclare : Warning<
+  "target-attribute based function overloads are not supported by NVCC and will be treated as a function redeclaration:"
+  "new declaration is %select{__device__|__global__|__host__|__host__ __device__}0 function, "
+  "old declaration is %select{__device__|__global__|__host__|__host__ __device__}1 function">,
+  InGroup<DiagGroup<"offload-incompatible-redeclare">>, DefaultIgnore;
 
 def err_cuda_device_builtin_surftex_cls_template : Error<
     "illegal device builtin %select{surface|texture}0 reference "
diff --git a/clang/lib/Sema/SemaCUDA.cpp b/clang/lib/Sema/SemaCUDA.cpp
index 80ea43dc5316e..580b9872c6a1d 100644
--- a/clang/lib/Sema/SemaCUDA.cpp
+++ b/clang/lib/Sema/SemaCUDA.cpp
@@ -1018,24 +1018,33 @@ void SemaCUDA::checkTargetOverload(FunctionDecl *NewFD,
     // HD/global functions "exist" in some sense on both the host and device, so
     // should have the same implementation on both sides.
     if (NewTarget != OldTarget &&
-        ((NewTarget == CUDAFunctionTarget::HostDevice &&
-          !(getLangOpts().OffloadImplicitHostDeviceTemplates &&
-            isImplicitHostDeviceFunction(NewFD) &&
-            OldTarget == CUDAFunctionTarget::Device)) ||
-         (OldTarget == CUDAFunctionTarget::HostDevice &&
-          !(getLangOpts().OffloadImplicitHostDeviceTemplates &&
-            isImplicitHostDeviceFunction(OldFD) &&
-            NewTarget == CUDAFunctionTarget::Device)) ||
-         (NewTarget == CUDAFunctionTarget::Global) ||
-         (OldTarget == CUDAFunctionTarget::Global)) &&
         !SemaRef.IsOverload(NewFD, OldFD, /* UseMemberUsingDeclRules = */ false,
                             /* ConsiderCudaAttrs = */ false)) {
-      Diag(NewFD->getLocation(), diag::err_cuda_ovl_target)
-          << llvm::to_underlying(NewTarget) << NewFD->getDeclName()
-          << llvm::to_underlying(OldTarget) << OldFD;
-      Diag(OldFD->getLocation(), diag::note_previous_declaration);
-      NewFD->setInvalidDecl();
-      break;
+      if ((NewTarget == CUDAFunctionTarget::HostDevice &&
+           !(getLangOpts().OffloadImplicitHostDeviceTemplates &&
+             isImplicitHostDeviceFunction(NewFD) &&
+             OldTarget == CUDAFunctionTarget::Device)) ||
+          (OldTarget == CUDAFunctionTarget::HostDevice &&
+           !(getLangOpts().OffloadImplicitHostDeviceTemplates &&
+             isImplicitHostDeviceFunction(OldFD) &&
+             NewTarget == CUDAFunctionTarget::Device)) ||
+          (NewTarget == CUDAFunctionTarget::Global) ||
+          (OldTarget == CUDAFunctionTarget::Global)) {
+        Diag(NewFD->getLocation(), diag::err_cuda_ovl_target)
+            << llvm::to_underlying(NewTarget) << NewFD->getDeclName()
+            << llvm::to_underlying(OldTarget) << OldFD;
+        Diag(OldFD->getLocation(), diag::note_previous_declaration);
+        NewFD->setInvalidDecl();
+        break;
+      }
+      if ((NewTarget == CUDAFunctionTarget::Host &&
+           OldTarget == CUDAFunctionTarget::Device) ||
+          (NewTarget == CUDAFunctionTarget::Device &&
+           OldTarget == CUDAFunctionTarget::Host)) {
+        Diag(NewFD->getLocation(), diag::warn_offload_incompatible_redeclare)
+            << llvm::to_underlying(NewTarget) << llvm::to_underlying(OldTarget);
+        Diag(OldFD->getLocation(), diag::note_previous_declaration);
+      }
     }
   }
 }
diff --git a/clang/test/SemaCUDA/function-redclare.cu b/clang/test/SemaCUDA/function-redclare.cu
new file mode 100644
index 0000000000000..b1d159a84b597
--- /dev/null
+++ b/clang/test/SemaCUDA/function-redclare.cu
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only \
+// RUN:   -isystem %S/Inputs -verify %s
+// RUN: %clang_cc1 -triple nvptx64-nvidia-cuda -fsyntax-only \
+// RUN:   -isystem %S/Inputs -fcuda-is-device -verify %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only \
+// RUN:   -isystem %S/Inputs -verify=redecl -Woffload-incompatible-redeclare %s
+// RUN: %clang_cc1 -triple nvptx64-nvidia-cuda -fsyntax-only \
+// RUN:   -isystem %S/Inputs -fcuda-is-device -Woffload-incompatible-redeclare -verify=redecl %s
+
+// expected-no-diagnostics
+#include "cuda.h"
+
+__device__ void f(); // redecl-note {{previous declaration is here}}
+
+void f() {} // redecl-warning {{target-attribute based function overloads are not supported by NVCC and will be treated as a function redeclaration:new declaration is __host__ function, old declaration is __device__ function}}
+
+void g(); // redecl-note {{previous declaration is here}}
+
+__device__ void g() {} // redecl-warning {{target-attribute based function overloads are not supported by NVCC and will be treated as a function redeclaration:new declaration is __device__ function, old declaration is __host__ function}}
diff --git a/llvm/docs/CompileCudaWithLLVM.rst b/llvm/docs/CompileCudaWithLLVM.rst
index 631691ef9b472..8c468d796660a 100644
--- a/llvm/docs/CompileCudaWithLLVM.rst
+++ b/llvm/docs/CompileCudaWithLLVM.rst
@@ -418,6 +418,17 @@ the compiler chooses to inline ``host_only``.
 Member functions, including constructors, may be overloaded using H and D
 attributes.  However, destructors cannot be overloaded.
 
+Clang Warnings for Host and Device Function Declarations
+--------------------------------------------------------
+
+Clang can emit warnings when it detects that host (H) and device (D) functions are declared or defined with the same signature. These warnings are not enabled by default.
+
+To enable these warnings, use the following compiler flag:
+
+.. code-block:: console
+
+    -Woffload-incompatible-redeclare
+
 Using a Different Class on Host/Device
 --------------------------------------