[Openmp-commits] [PATCH] D101663: [OpenMP] Avoid unintentional use of host compiler as bclib compiler.

[Michael Kruse via Phabricator via Openmp-commits]

Meinersbur created this revision.
Meinersbur added reviewers: tianshilei1992, jdoerfert, protze.joachim.
Meinersbur added a project: OpenMP.
Herald added subscribers: guansong, yaxunl, mgorny.
Meinersbur requested review of this revision.
Herald added subscribers: llvm-commits, sstefan1.
Herald added a project: LLVM.

Before this patch, libomptarget assumed that if the host compiler is clang, then it is also suitable for compile CUDA to LLVM-IR. The intention was that if libomptarget is compiled using `LLVM_ENABLE_RUMTIMES=openmp`, the host compiler will be clang from the same propository.

However, the host compiler may also be clang when compiling as a `LLVM_ENABLE_PROJECTS=openmp` or standalone build if the user explicitly set the tool chain or, clang is the system's default compiler (MacOS, most BSDs). Various vendor compilers such as Apple's clang, Intel's dpcpp/icx, IBM's xlclang, etc. may be identified as 'clang' by CMake. However, these potentially use an incompatible IR, or stripped CUDA support, with unpredictable results.

Fix by explicitly set LIBOMPTARGET_NVPTX_CUDA_COMPILER (and LIBOMPTARGET_NVPTX_BC_LINKER) when using `LLVM_ENABLE_RUMTIMES=openmp` and do not try to use the host compiler.

Implementation of discussion in D101265 <https://reviews.llvm.org/D101265>. Compilation result: http://meinersbur.de:8011/#/builders/143/builds/375


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D101663

Files:
  llvm/runtimes/CMakeLists.txt
  openmp/libomptarget/deviceRTLs/nvptx/CMakeLists.txt


Index: openmp/libomptarget/deviceRTLs/nvptx/CMakeLists.txt
===================================================================
--- openmp/libomptarget/deviceRTLs/nvptx/CMakeLists.txt
+++ openmp/libomptarget/deviceRTLs/nvptx/CMakeLists.txt
@@ -33,15 +33,6 @@
 elseif (LLVM_TOOL_CLANG_BUILD AND NOT CMAKE_CROSSCOMPILING)
   # Compile the deviceRTL with the clang that is built in the project.
   set(cuda_compiler "$<TARGET_FILE:clang>")
-elseif(${CMAKE_C_COMPILER_ID} STREQUAL "Clang")
-  # Compile the device runtime with the compiler that OpenMP is built with.
-  # This is the case with LLVM_ENABLE_RUNTIMES=openmp.
-  # FIXME: This is unreliable; the compiler can be on older version of clang
-  # that does not support compiling CUDA, or only an older version of it. The
-  # risk is especially high on sytems where clang is the default compiler
-  # (MacOS, BSDs). LLVM_ENABLE_RUNTIMES=openmp should itself set
-  # LIBOMPTARGET_NVPTX_CUDA_COMPILER instead.
-  set(cuda_compiler ${CMAKE_C_COMPILER})
 else()
   libomptarget_say("Not building NVPTX deviceRTL: clang not found")
   return()
Index: llvm/runtimes/CMakeLists.txt
===================================================================
--- llvm/runtimes/CMakeLists.txt
+++ llvm/runtimes/CMakeLists.txt
@@ -235,6 +235,8 @@
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
+                                      -DLIBOMPTARGET_NVPTX_CUDA_COMPILER=$<TARGET_FILE:clang>
+                                      -DLIBOMPTARGET_NVPTX_BC_LINKER=$<TARGET_FILE:llvm-link>
                                       ${RUNTIMES_CMAKE_ARGS}
                            PASSTHROUGH_PREFIXES LLVM_ENABLE_RUNTIMES
                                                 ${ARG_PREFIXES}
@@ -335,6 +337,8 @@
                                       -DCMAKE_C_COMPILER_WORKS=ON
                                       -DCMAKE_CXX_COMPILER_WORKS=ON
                                       -DCMAKE_ASM_COMPILER_WORKS=ON
+                                      -DLIBOMPTARGET_NVPTX_CUDA_COMPILER=$<TARGET_FILE:clang>
+                                      -DLIBOMPTARGET_NVPTX_BC_LINKER=$<TARGET_FILE:llvm-link>
                                       -DCOMPILER_RT_DEFAULT_TARGET_ONLY=ON
                                       -DLLVM_RUNTIMES_TARGET=${name}
                                       ${${name}_extra_args}


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