[libclc] [llvm] [libclc] Support LLVM_ENABLE_RUNTIMES when building (PR #141574)

[Fraser Cormack via cfe-commits]

https://github.com/frasercrmck created https://github.com/llvm/llvm-project/pull/141574

This commit deprecates the use of LLVM_ENABLE_PROJECTS in favour of LLVM_ENABLE_RUNTIMES.

Alternatively, using -DLLVM_RUNTIME_TARGETS=<triple> combined with -DRUNTIMES_<triple>_LLVM_ENABLE_RUNTIMES=libclc also gets pretty far but fails due to zlib problems building the LLVM utility 'prepare_builtins'. I'm not sure what's going on there but I don't think it's required at this stage. More work would be required to support that option.

This does nothing to change how the host tools are found in order to be used to actually build the libclc libraries.

Fixes #124013.

>From f5278d261d203cea8889174c8b0a16c03d1cbad9 Mon Sep 17 00:00:00 2001
From: Fraser Cormack <fraser at codeplay.com>
Date: Tue, 27 May 2025 11:11:14 +0100
Subject: [PATCH] [libclc] Support LLVM_ENABLE_RUNTIMES when building

This commit deprecates the use of LLVM_ENABLE_PROJECTS in favour of
LLVM_ENABLE_RUNTIMES.

Alternatively, using -DLLVM_RUNTIME_TARGETS=<triple> combined with
-DRUNTIMES_<triple>_LLVM_ENABLE_RUNTIMES=libclc also gets pretty far but
fails due to zlib problems building the LLVM utility 'prepare_builtins'.
I'm not sure what's going on there but I don't think it's required at
this stage. More work would be required to support that option.

This does nothing to change how the host tools are found in order to be
used to actually build the libclc libraries.

Fixes #124013.
---
 libclc/CMakeLists.txt        | 2 +-
 llvm/CMakeLists.txt          | 9 ++++++++-
 llvm/runtimes/CMakeLists.txt | 2 +-
 runtimes/CMakeLists.txt      | 2 +-
 4 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/libclc/CMakeLists.txt b/libclc/CMakeLists.txt
index 0d9a21c6d63a9..657cab713f8d9 100644
--- a/libclc/CMakeLists.txt
+++ b/libclc/CMakeLists.txt
@@ -72,7 +72,7 @@ else()
   # Note that we check this later (for both build types) but we can provide a
   # more useful error message when built in-tree. We assume that LLVM tools are
   # always available so don't warn here.
-  if( NOT clang IN_LIST LLVM_ENABLE_PROJECTS )
+  if( NOT LLVM_RUNTIMES_BUILD AND NOT clang IN_LIST LLVM_ENABLE_PROJECTS )
     message(FATAL_ERROR "Clang is not enabled, but is required to build libclc in-tree")
   endif()
 
diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index ed44b16bf9aeb..b27ea78eb5e6c 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -136,7 +136,7 @@ endforeach()
 # As we migrate runtimes to using the bootstrapping build, the set of default runtimes
 # should grow as we remove those runtimes from LLVM_ENABLE_PROJECTS above.
 set(LLVM_DEFAULT_RUNTIMES "libcxx;libcxxabi;libunwind")
-set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc;offload;flang-rt")
+set(LLVM_SUPPORTED_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;llvm-libgcc;offload;flang-rt;libclc")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")
 if(LLVM_ENABLE_RUNTIMES STREQUAL "all")
@@ -200,6 +200,13 @@ if ("flang-rt" IN_LIST LLVM_ENABLE_RUNTIMES)
   endif ()
 endif ()
 
+if ("libclc" IN_LIST LLVM_ENABLE_PROJECTS)
+  message(WARNING "Using LLVM_ENABLE_PROJECTS=libclc is deprecated now, and will "
+    "become a fatal error in the LLVM 21 release.  Please use "
+    "-DLLVM_ENABLE_RUNTIMES=libclc or see the instructions at "
+    "https://libclc.llvm.org/ for building the runtimes.")
+endif()
+
 # Set a shorthand option to enable the GPU build of the 'libc' project.
 option(LIBC_GPU_BUILD "Enable the 'libc' project targeting the GPU" OFF)
 if(LIBC_GPU_BUILD)
diff --git a/llvm/runtimes/CMakeLists.txt b/llvm/runtimes/CMakeLists.txt
index cabadfc9184f8..9f86650ec58d1 100644
--- a/llvm/runtimes/CMakeLists.txt
+++ b/llvm/runtimes/CMakeLists.txt
@@ -193,7 +193,7 @@ endif()
 
 function(_get_runtime_name name out_var)
   string(FIND ${name} "lib" idx)
-  if(idx EQUAL 0 AND NOT ${name} STREQUAL "libc")
+  if(idx EQUAL 0 AND NOT (${name} STREQUAL "libc" OR ${name} STREQUAL "libclc"))
     string(SUBSTRING ${name} 3 -1 name)
   endif()
   set(${out_var} ${name} PARENT_SCOPE)
diff --git a/runtimes/CMakeLists.txt b/runtimes/CMakeLists.txt
index 7f1e2ae065d6c..c62a6c7e8d2b3 100644
--- a/runtimes/CMakeLists.txt
+++ b/runtimes/CMakeLists.txt
@@ -35,7 +35,7 @@ list(INSERT CMAKE_MODULE_PATH 0
 
 # We order libraries to mirror roughly how they are layered, except that compiler-rt can depend
 # on libc++, so we put it after.
-set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;offload")
+set(LLVM_DEFAULT_RUNTIMES "libc;libunwind;libcxxabi;pstl;libcxx;compiler-rt;openmp;offload;libclc")
 set(LLVM_SUPPORTED_RUNTIMES "${LLVM_DEFAULT_RUNTIMES};llvm-libgcc;flang-rt")
 set(LLVM_ENABLE_RUNTIMES "" CACHE STRING
   "Semicolon-separated list of runtimes to build, or \"all\" (${LLVM_DEFAULT_RUNTIMES}). Supported runtimes are ${LLVM_SUPPORTED_RUNTIMES}.")