[clang][Fuchsia] Add relative-vtables multilib

[leonardchan]

Summary

This adds multilibs for Fuchsia that is built with the relative vtables ABI, one with and another without exceptions.

[leonardchan]

This should also be ready now that https://reviews.llvm.org/D85802 landed, unless we don't want to submit this *right* now so the clang builders don't build these multilibs that won't be used yet?

[phosek]

In D85576#2330923, @leonardchan wrote:

This should also be ready now that https://reviews.llvm.org/D85802 landed, unless we don't want to submit this *right* now so the clang builders don't build these multilibs that won't be used yet?

This change implement a slightly different approach from what we discussed, which is providing an Itanium-compatible (that is -fc++abi=itanium) multilib for compatibility with other compilers, and then enabling relative vtables by default. Unless there's a strong reason not to take that approach, that's the direction I'd prefer.

[leonardchan]

This change implement a slightly different approach from what we discussed, which is providing an Itanium-compatible (that is -fc++abi=itanium) multilib for compatibility with other compilers, and then enabling relative vtables by default. Unless there's a strong reason not to take that approach, that's the direction I'd prefer.

Ah, yeah I just forgot about that. Will update accoringly.

[leonardchan]

Updated to use the -fexperimental-relative-c++-ab-vtables flag now that D85802 was reverted. This will be used for the purpose of testing the relative vtables ABI in Fuchsia CQ builders to ensure all tests are run, accounting for flakes. The end goal will involve not having a relative vtables multilib, but instead making it the default for the fuchsia ABI, and instead having a separate Itanium multilib for supporting GCC.

[leonardchan]

*ping* any more comments on this patch?

[phosek]

LGTM

clang/cmake/caches/Fuchsia-stage2.cmake

foreach(target x86_64;aarch64)
 
     set(RUNTIMES_${target}-unknown-fuchsia+asan+noexcept_LLVM_BUILD_COMPILER_RT OFF CACHE BOOL "")
     set(RUNTIMES_${target}-unknown-fuchsia+asan+noexcept_LLVM_USE_SANITIZER "Address" CACHE STRING "")
     set(RUNTIMES_${target}-unknown-fuchsia+asan+noexcept_LIBCXXABI_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}-unknown-fuchsia+asan+noexcept_LIBCXX_ENABLE_NEW_DELETE_DEFINITIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}-unknown-fuchsia+asan+noexcept_LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
     set(RUNTIMES_${target}-unknown-fuchsia+asan+noexcept_LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
 
+    set(RUNTIMES_${target}-unknown-fuchsia+relative-vtables_LLVM_BUILD_COMPILER_RT OFF CACHE BOOL "")
+    set(RUNTIMES_${target}-unknown-fuchsia+relative-vtables_CMAKE_CXX_FLAGS "${RUNTIMES_${target}-unknown-fuchsia+relative-vtables_CMAKE_CXX_FLAGS} -Xclang -fexperimental-relative-c++-abi-vtables" CACHE STRING "")
+
+    set(RUNTIMES_${target}-unknown-fuchsia+relative-vtables+noexcept_LLVM_BUILD_COMPILER_RT OFF CACHE BOOL "")
+    set(RUNTIMES_${target}-unknown-fuchsia+relative-vtables+noexcept_CMAKE_CXX_FLAGS "${RUNTIMES_${target}-unknown-fuchsia+relative-vtables+noexcept_CMAKE_CXX_FLAGS} -Xclang -fexperimental-relative-c++-abi-vtables" CACHE STRING "")
+    set(RUNTIMES_${target}-unknown-fuchsia+relative-vtables+noexcept_LIBCXXABI_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+    set(RUNTIMES_${target}-unknown-fuchsia+relative-vtables+noexcept_LIBCXX_ENABLE_EXCEPTIONS OFF CACHE BOOL "")
+
     # Use .build-id link.
     list(APPEND RUNTIME_BUILD_ID_LINK "${target}-unknown-fuchsia")
   endforeach()
 
-  set(LLVM_RUNTIME_MULTILIBS "asan;noexcept;asan+noexcept" CACHE STRING "")
+  set(LLVM_RUNTIME_MULTILIBS "asan;noexcept;asan+noexcept;relative-vtables;relative-vtables+noexcept" CACHE STRING "")
   set(LLVM_RUNTIME_MULTILIB_asan_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
   set(LLVM_RUNTIME_MULTILIB_noexcept_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
   set(LLVM_RUNTIME_MULTILIB_asan+noexcept_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
+  set(LLVM_RUNTIME_MULTILIB_relative-vtables_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
+  set(LLVM_RUNTIME_MULTILIB_relative-vtables+noexcept_TARGETS "x86_64-unknown-fuchsia;aarch64-unknown-fuchsia" CACHE STRING "")
 endif()
 
 set(LLVM_BUILTIN_TARGETS "${BUILTIN_TARGETS}" CACHE STRING "")
 set(LLVM_RUNTIME_TARGETS "${RUNTIME_TARGETS}" CACHE STRING "")
 set(LLVM_RUNTIME_BUILD_ID_LINK_TARGETS "${RUNTIME_BUILD_ID_LINK}" CACHE STRING "")
 
 # Setup toolchain.
 set(LLVM_INSTALL_TOOLCHAIN_ONLY ON CACHE BOOL "")

clang/lib/Driver/ToolChains/Fuchsia.cpp

Fuchsia::Fuchsia(const Driver &D, const llvm::Triple &Triple,
   // ASan has higher priority because we always want the instrumentated version.
   Multilibs.push_back(Multilib("asan", {}, {}, 2)
                           .flag("+fsanitize=address"));
   // Use the asan+noexcept variant with ASan and -fno-exceptions.
   Multilibs.push_back(Multilib("asan+noexcept", {}, {}, 3)
                           .flag("+fsanitize=address")
                           .flag("-fexceptions")
                           .flag("+fno-exceptions"));
+  // Use the relative vtables ABI.
+  Multilibs.push_back(Multilib("relative-vtables", {}, {}, 4)
+                          .flag("+fexperimental-relative-c++-abi-vtables"));
+  Multilibs.push_back(Multilib("relative-vtables+noexcept", {}, {}, 5)
+                          .flag("+fexperimental-relative-c++-abi-vtables")
+                          .flag("-fexceptions")
+                          .flag("+fno-exceptions"));
   Multilibs.FilterOut([&](const Multilib &M) {
     std::vector<std::string> RD = FilePaths(M);
     return std::all_of(RD.begin(), RD.end(), [&](std::string P) {
       return !getVFS().exists(P);
     });
   });
 
   Multilib::flags_list Flags;
   addMultilibFlag(
       Args.hasFlag(options::OPT_fexceptions, options::OPT_fno_exceptions, true),
       "fexceptions", Flags);
   addMultilibFlag(getSanitizerArgs().needsAsanRt(), "fsanitize=address", Flags);
+
+  addMultilibFlag(
+      Args.hasFlag(options::OPT_fexperimental_relative_cxx_abi_vtables,
+                   options::OPT_fno_experimental_relative_cxx_abi_vtables,
+                   /*default=*/false),
+      "fexperimental-relative-c++-abi-vtables", Flags);
+
   Multilibs.setFilePathsCallback(FilePaths);
 
   if (Multilibs.select(Flags, SelectedMultilib))
     if (!SelectedMultilib.isDefault())
       if (const auto &PathsCallback = Multilibs.filePathsCallback())
         for (const auto &Path : PathsCallback(SelectedMultilib))
           // Prepend the multilib path to ensure it takes the precedence.
           getFilePaths().insert(getFilePaths().begin(), Path);

clang/test/Driver/fuchsia.cpp

 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld 2>&1\
 // RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-NOEXCEPT-X86
 // RUN: %clangxx %s -### --target=x86_64-fuchsia -fsanitize=address -fno-exceptions \
 // RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
 // RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
 // RUN:     -fuse-ld=lld 2>&1\
 // RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-ASAN-NOEXCEPT-X86
+// RUN: %clangxx %s -### --target=x86_64-fuchsia -fexperimental-relative-c++-abi-vtables \
+// RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:     -fuse-ld=lld 2>&1\
+// RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-RELATIVE-VTABLES-X86
+// RUN: %clangxx %s -### --target=x86_64-fuchsia -fexperimental-relative-c++-abi-vtables -fno-exceptions \
+// RUN:     -ccc-install-dir %S/Inputs/basic_fuchsia_tree/bin \
+// RUN:     -resource-dir=%S/Inputs/resource_dir_with_per_target_subdir \
+// RUN:     -fuse-ld=lld 2>&1\
+// RUN:     | FileCheck %s -check-prefixes=CHECK-MULTILIB-X86,CHECK-MULTILIB-RELATIVE-VTABLES-NOEXCEPT-X86
 // CHECK-MULTILIB-X86: "-resource-dir" "[[RESOURCE_DIR:[^"]+]]"
 // CHECK-MULTILIB-ASAN-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}asan"
 // CHECK-MULTILIB-NOEXCEPT-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}noexcept"
 // CHECK-MULTILIB-ASAN-NOEXCEPT-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}asan+noexcept"
+// CHECK-MULTILIB-RELATIVE-VTABLES-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}relative-vtables"
+// CHECK-MULTILIB-RELATIVE-VTABLES-NOEXCEPT-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++{{/|\\\\}}relative-vtables+noexcept"
 // CHECK-MULTILIB-X86: "-L{{.*}}{{/|\\\\}}..{{/|\\\\}}lib{{/|\\\\}}x86_64-fuchsia{{/|\\\\}}c++"