[clang] [openmp] [OpenMP] Respect LLVM per-target install directories (PR #83282)

[Joseph Huber via cfe-commits]

https://github.com/jhuber6 created https://github.com/llvm/llvm-project/pull/83282

Summary:
One recurring problem we have with the OpenMP libraries is that they are
potentially conflicting with ones found on the system, this occurs when
there are two copies and one is used for linking that it not attached to
the correspoding clang compiler. LLVM already uses target specific
directories for this, like with libc++, which are always searched first.
This patch changes the install directory to be
`lib/x86_64-unknown-linux-gnu` for example.

Notable changes would be that users will need to change their
LD_LIBRARY_PATH settings optionally, or use default rt-rpath options.
This should fix problems were users are linking the wrong versions of
static libraries


>From 13389e98533eb287514bcbca6a4333e887a8a514 Mon Sep 17 00:00:00 2001
From: Joseph Huber <huberjn at outlook.com>
Date: Wed, 28 Feb 2024 09:57:30 -0600
Subject: [PATCH] [OpenMP] Respect LLVM per-target install directories

Summary:
One recurring problem we have with the OpenMP libraries is that they are
potentially conflicting with ones found on the system, this occurs when
there are two copies and one is used for linking that it not attached to
the correspoding clang compiler. LLVM already uses target specific
directories for this, like with libc++, which are always searched first.
This patch changes the install directory to be
`lib/x86_64-unknown-linux-gnu` for example.

Notable changes would be that users will need to change their
LD_LIBRARY_PATH settings optionally, or use default rt-rpath options.
This should fix problems were users are linking the wrong versions of
static libraries
---
 clang/lib/Driver/ToolChains/CommonArgs.cpp | 10 +++++-----
 clang/lib/Driver/ToolChains/CommonArgs.h   |  3 ++-
 clang/lib/Driver/ToolChains/Cuda.cpp       |  2 +-
 openmp/CMakeLists.txt                      | 12 +++++++++---
 4 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index faceee85a2f8dc..382c8b3612a0af 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -2763,13 +2763,13 @@ void tools::addOpenMPDeviceRTL(const Driver &D,
                                const llvm::opt::ArgList &DriverArgs,
                                llvm::opt::ArgStringList &CC1Args,
                                StringRef BitcodeSuffix,
-                               const llvm::Triple &Triple) {
+                               const llvm::Triple &Triple,
+                               const ToolChain &HostTC) {
   SmallVector<StringRef, 8> LibraryPaths;
 
-  // Add path to clang lib / lib64 folder.
-  SmallString<256> DefaultLibPath = llvm::sys::path::parent_path(D.Dir);
-  llvm::sys::path::append(DefaultLibPath, CLANG_INSTALL_LIBDIR_BASENAME);
-  LibraryPaths.emplace_back(DefaultLibPath.c_str());
+  // Check all of the standard library search paths used by the compiler.
+  for (const auto &LibPath : HostTC.getFilePaths())
+    LibraryPaths.emplace_back(LibPath);
 
   // Add user defined library paths from LIBRARY_PATH.
   std::optional<std::string> LibPath =
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.h b/clang/lib/Driver/ToolChains/CommonArgs.h
index 2db0f889ca8209..b8f649aab4bdd2 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.h
+++ b/clang/lib/Driver/ToolChains/CommonArgs.h
@@ -214,7 +214,8 @@ void addMachineOutlinerArgs(const Driver &D, const llvm::opt::ArgList &Args,
 
 void addOpenMPDeviceRTL(const Driver &D, const llvm::opt::ArgList &DriverArgs,
                         llvm::opt::ArgStringList &CC1Args,
-                        StringRef BitcodeSuffix, const llvm::Triple &Triple);
+                        StringRef BitcodeSuffix, const llvm::Triple &Triple,
+                        const ToolChain &HostTC);
 
 void addOutlineAtomicsArgs(const Driver &D, const ToolChain &TC,
                            const llvm::opt::ArgList &Args,
diff --git a/clang/lib/Driver/ToolChains/Cuda.cpp b/clang/lib/Driver/ToolChains/Cuda.cpp
index ff3687ca7dae33..177fd6310e7ee2 100644
--- a/clang/lib/Driver/ToolChains/Cuda.cpp
+++ b/clang/lib/Driver/ToolChains/Cuda.cpp
@@ -903,7 +903,7 @@ void CudaToolChain::addClangTargetOptions(
       return;
 
     addOpenMPDeviceRTL(getDriver(), DriverArgs, CC1Args, GpuArch.str(),
-                       getTriple());
+                       getTriple(), HostTC);
   }
 }
 
diff --git a/openmp/CMakeLists.txt b/openmp/CMakeLists.txt
index 03068af22629f7..3c4ff76ad6d161 100644
--- a/openmp/CMakeLists.txt
+++ b/openmp/CMakeLists.txt
@@ -46,9 +46,15 @@ if (OPENMP_STANDALONE_BUILD)
   set(CMAKE_CXX_EXTENSIONS NO)
 else()
   set(OPENMP_ENABLE_WERROR ${LLVM_ENABLE_WERROR})
-  # If building in tree, we honor the same install suffix LLVM uses.
-  set(OPENMP_INSTALL_LIBDIR "lib${LLVM_LIBDIR_SUFFIX}" CACHE STRING
-      "Path where built OpenMP libraries should be installed.")
+
+  # When building in tree we install the runtime according to the LLVM settings.
+  if(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR AND NOT APPLE)
+    set(OPENMP_INSTALL_LIBDIR lib${LLVM_LIBDIR_SUFFIX}/${LLVM_DEFAULT_TARGET_TRIPLE} CACHE STRING
+        "Path where built openmp libraries should be installed.")
+  else()
+    set(OPENMP_INSTALL_LIBDIR "lib${LLVM_LIBDIR_SUFFIX}" CACHE STRING
+        "Path where built OpenMP libraries should be installed.")
+  endif()
 
   if (NOT MSVC)
     set(OPENMP_TEST_C_COMPILER ${LLVM_RUNTIME_OUTPUT_INTDIR}/clang)