[PATCH] D109719: [runtimes] Check whether -nostdinc++ and -nostdlib++ are supported

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo updated this revision to Diff 372439.
mstorsjo added a comment.
Herald added a project: libc++.
Herald added a subscriber: libcxx-commits.
Herald added a reviewer: libc++.
This revision now requires review to proceed.

Reuploading with a dummy change under libcxx, to trigger rerunning the libcxx premerge tests with this change, will remove that before pushing.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109719/new/

https://reviews.llvm.org/D109719

Files:
  libcxx/CMakeLists.txt
  runtimes/CMakeLists.txt


Index: runtimes/CMakeLists.txt
===================================================================
--- runtimes/CMakeLists.txt
+++ runtimes/CMakeLists.txt
@@ -87,12 +87,19 @@
 
 include(CheckLibraryExists)
 include(CheckCCompilerFlag)
-
-# Disable use of the installed C++ standard library when building runtimes. If
-# MSVC is true, we must be using the clang-cl driver, which doesn't understand
-# these flags.
-if (NOT MSVC)
-  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdinc++ -nostdlib++")
+include(CheckCXXCompilerFlag)
+
+# Disable use of the installed C++ standard library when building runtimes.
+# Check for -nostdlib++ first; if there's no C++ standard library yet,
+# all check_cxx_compiler_flag commands will fail until we add -nostdlib++
+# (or -nodefaultlibs).
+check_c_compiler_flag(-nostdlib++ LLVM_RUNTIMES_SUPPORT_NOSTDLIBXX_FLAG)
+if (LLVM_RUNTIMES_SUPPORT_NOSTDLIBXX_FLAG)
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdlib++")
+endif()
+check_cxx_compiler_flag(-nostdinc++ LLVM_RUNTIMES_SUPPORT_NOSTDINCXX_FLAG)
+if (LLVM_RUNTIMES_SUPPORT_NOSTDINCXX_FLAG)
+  set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -nostdinc++")
 endif()
 
 # Avoid checking whether the compiler is working.
Index: libcxx/CMakeLists.txt
===================================================================
--- libcxx/CMakeLists.txt
+++ libcxx/CMakeLists.txt
@@ -1,5 +1,6 @@
 # See https://libcxx.llvm.org/docs/BuildingLibcxx.html for instructions on how
 # to build libcxx with CMake.
+# Dummy change.
 
 if (NOT IS_DIRECTORY "${CMAKE_CURRENT_LIST_DIR}/../libcxxabi")
   message(FATAL_ERROR "libc++ now requires being built in a monorepo layout with libcxxabi available")


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