[llvm-branch-commits] [llvm] 6349865 - [CMake] Don't use -fno-semantic-interposition with Clang<=13

[Tom Stellard via llvm-branch-commits]

Author: Fangrui Song
Date: 2022-01-20T13:29:49-08:00
New Revision: 6349865a8f3751a651f9451eac0405e01ee03a11

URL: https://github.com/llvm/llvm-project/commit/6349865a8f3751a651f9451eac0405e01ee03a11
DIFF: https://github.com/llvm/llvm-project/commit/6349865a8f3751a651f9451eac0405e01ee03a11.diff

LOG: [CMake] Don't use -fno-semantic-interposition with Clang<=13

Clang 13 has a -fsanitize-coverage -fno-semantic-interposition bug (D117190)
which may lead to
`relocation R_X86_64_PC32 cannot be used against symbol` linker error
in -DLLVM_USE_SANITIZE_COVERAGE=ON build when a shared object is built (e.g.
-DLLVM_BUILD_LLVM_DYLIB=on).

For simplicity, just disallow Clang 13 entirely.

Note: GCC -fPIC performance benefits from -fno-semantic-interposition
dramatically. Clang benefits little. Using this option is more for a dogfood
purpose to test correctness of this option, because in the wild some important
packages like CPython uses this option.

Differential Revision: https://reviews.llvm.org/D117183

(cherry picked from commit 1661c8cfcd6b286a1b5a599544afd87aa6b90243)

Added: 
    

Modified: 
    llvm/cmake/modules/HandleLLVMOptions.cmake

Removed: 
    


################################################################################
diff  --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 0c3419390c275..cfcbb8f8aec37 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -316,12 +316,11 @@ if( LLVM_ENABLE_PIC )
     # Note: GCC<10.3 has a bug on SystemZ.
     #
     # Note: Clang allows IPO for -fPIC so this optimization is less effective.
-    # Older Clang may support -fno-semantic-interposition but it used local
-    # aliases to optimize global variables, which is incompatible with copy
-    # relocations due to -fno-pic.
+    # Clang 13 has a bug related to -fsanitize-coverage
+    # -fno-semantic-interposition (https://reviews.llvm.org/D117183).
     if ((CMAKE_COMPILER_IS_GNUCXX AND
          NOT (LLVM_NATIVE_ARCH STREQUAL "SystemZ" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 10.3))
-       OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION GREATER_EQUAL 13))
+       OR (CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION GREATER_EQUAL 14))
       add_flag_if_supported("-fno-semantic-interposition" FNO_SEMANTIC_INTERPOSITION)
     endif()
   endif()