Merge pull request #31053 from drexin/wip-backport-atomics-fix

[5.2] Remove dependency on libatomic on Linux

Author: tkremenek

cmake/modules/AddSwift.cmake

@@ -363,6 +363,13 @@ function(_add_variant_c_compile_flags)
    endif()
   endif()
 
+  if("${CFLAGS_SDK}" STREQUAL "LINUX")
+    if(${CFLAGS_ARCH} STREQUAL x86_64)
+      # this is the minimum architecture that supports 16 byte CAS, which is necessary to avoid a dependency to libatomic
+      list(APPEND result "-march=core2")
+    endif()
+  endif()
+
   set("${CFLAGS_RESULT_VAR_NAME}" "${result}" PARENT_SCOPE)
 endfunction()
 
@@ -460,7 +467,7 @@ function(_add_variant_link_flags)
     RESULT_VAR_NAME result)
 
   if("${LFLAGS_SDK}" STREQUAL "LINUX")
-    list(APPEND link_libraries "pthread" "atomic" "dl")
+    list(APPEND link_libraries "pthread" "dl")
   elseif("${LFLAGS_SDK}" STREQUAL "FREEBSD")
     list(APPEND link_libraries "pthread")
   elseif("${LFLAGS_SDK}" STREQUAL "CYGWIN")

cmake/modules/AddSwiftUnittests.cmake

@@ -48,8 +48,10 @@ function(add_swift_unittest test_dirname)
       "${android_system_libs}")
     set_property(TARGET "${test_dirname}" APPEND PROPERTY LINK_LIBRARIES "log")
   elseif("${CMAKE_SYSTEM_NAME}" STREQUAL "Linux")
-    set_property(TARGET "${test_dirname}" APPEND PROPERTY LINK_LIBRARIES
-      "atomic")
+    if(CMAKE_SYSTEM_PROCESSOR MATCHES "x86_64|AMD64")
+      target_compile_options(${test_dirname} PRIVATE
+        -march=core2)
+    endif()
   endif()
 
   find_program(LDLLD_PATH "ld.lld")

stdlib/public/SwiftShims/RefCount.h

@@ -589,7 +589,7 @@ class RefCountBitsT {
 
 typedef RefCountBitsT<RefCountIsInline> InlineRefCountBits;
 
-class SideTableRefCountBits : public RefCountBitsT<RefCountNotInline>
+class alignas(sizeof(void*) * 2) SideTableRefCountBits : public RefCountBitsT<RefCountNotInline>
 {
   uint32_t weakBits;
 

stdlib/public/runtime/Metadata.cpp

@@ -5054,7 +5054,7 @@ void swift::checkMetadataDependencyCycle(const Metadata *startMetadata,
 /***************************************************************************/
 
 namespace {
-  struct PoolRange {
+  struct alignas(sizeof(uintptr_t) * 2) PoolRange {
     static constexpr uintptr_t PageSize = 16 * 1024;
     static constexpr uintptr_t MaxPoolAllocationSize = PageSize / 2;
 

unittests/runtime/CMakeLists.txt

@@ -50,8 +50,6 @@ if(("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "${SWIFT_PRIMARY_VARIANT_SDK}") AND
       ${FOUNDATION_LIBRARY}
       swiftStdlibUnittest${SWIFT_PRIMARY_VARIANT_SUFFIX}
       )
-  elseif(SWIFT_HOST_VARIANT STREQUAL "linux")
-    list(APPEND PLATFORM_TARGET_LINK_LIBRARIES "atomic")
   elseif(SWIFT_HOST_VARIANT STREQUAL "freebsd")
     find_library(EXECINFO_LIBRARY execinfo)
     list(APPEND PLATFORM_TARGET_LINK_LIBRARIES

unittests/runtime/LongTests/CMakeLists.txt

@@ -19,10 +19,6 @@ if(("${SWIFT_HOST_VARIANT_SDK}" STREQUAL "${SWIFT_PRIMARY_VARIANT_SDK}") AND
 
     # Link the Objective-C runtime.
     list(APPEND PLATFORM_TARGET_LINK_LIBRARIES "objc")
-  elseif(SWIFT_HOST_VARIANT STREQUAL "linux")
-    list(APPEND PLATFORM_TARGET_LINK_LIBRARIES
-      "atomic"
-      )
   elseif(SWIFT_HOST_VARIANT STREQUAL "freebsd")
     find_library(EXECINFO_LIBRARY execinfo)
     list(APPEND PLATFORM_TARGET_LINK_LIBRARIES

utils/gen-static-stdlib-link-args

@@ -61,9 +61,7 @@ function write_linkfile {
     cat >$OUTPUTFILE <<EOF
 -ldl
 -lpthread
--latomic
 -lswiftCore
--latomic
 -lswiftImageInspectionShared
 $ICU_LIBS
 -lstdc++

utils/static-executable-args.lnk

@@ -8,7 +8,6 @@
 -Xlinker
 --defsym=__import_pthread_key_create=pthread_key_create
 -lpthread
--latomic
 -licui18n
 -licuuc
 -licudata