An attempt to abandon omptarget out-of-tree builds.

I want to start using LLVM component libraries in libomptarget
to stop duplicating implementations already available in LLVM
(e.g. LLVMObject, LLVMSupport, etc.). Without relying on LLVM
in all libomptarget builds one has to provide fallback implementation
for each used LLVM feature.

This is an attempt to stop supporting out-of-llvm-tree builds of libomptarget.

I understand that I may need to revert this,
if this affects downstream projects in a bad way.

Differential Revision: https://reviews.llvm.org/D101509

1 files changed, 9 insertions, 0 deletions

diff --git a/openmp/README.rst b/openmp/README.rst
index 59301c513d59..bd8071f43f95 100644
--- a/openmp/README.rst
+++ b/openmp/README.rst
@@ -243,6 +243,15 @@ These flags are **appended**, they do not overwrite any of the preset flags.
 Options for ``libomptarget``
 ----------------------------
 
+An installed LLVM package is a prerequisite for building ``libomptarget``
+library. So ``libomptarget`` may only be built in two cases:
+
+- As a project of a regular LLVM build via **LLVM_ENABLE_PROJECTS**,
+  **LLVM_EXTERNAL_PROJECTS**, or **LLVM_ENABLE_RUNTIMES** or
+- as a standalone project build that uses a pre-installed LLVM package.
+  In this mode one has to make sure that the default CMake
+  ``find_package(LLVM)`` call `succeeds <https://cmake.org/cmake/help/latest/command/find_package.html#search-procedure>`_.
+
 **LIBOMPTARGET_OPENMP_HEADER_FOLDER** = ``""``
   Path of the folder that contains ``omp.h``.  This is required for testing
   out-of-tree builds.