[llvm-dev] Linker failures in debug build - compiler/linker poll?

[Nicolai Hähnle via llvm-dev]

Hi,

since recently I'm getting linker failures in debug builds. The root 
cause is that -fvisibility-inlines-hidden causes inline functions in 
explicit template instantiations to become hidden in certain cases.

The following hunk works around this...

--- a/cmake/modules/HandleLLVMOptions.cmake
+++ b/cmake/modules/HandleLLVMOptions.cmake
@@ -159,7 +159,13 @@ endif()
  if(NOT WIN32 AND NOT CYGWIN)
    # MinGW warns if -fvisibility-inlines-hidden is used.
    check_cxx_compiler_flag("-fvisibility-inlines-hidden" 
SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG)
-  append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG 
"-fvisibility-inlines-hidden" CMAKE_CXX_FLAGS)
+
+  # The flag also hides inlines from explicit template instantiations, 
which
+  # leads to link failures in debug builds at least with gcc 5.3.1 and
+  # both GNU ld 2.26 or gold 1.11.
+  if (NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+    append_if(SUPPORTS_FVISIBILITY_INLINES_HIDDEN_FLAG 
"-fvisibility-inlines-hidden" CMAKE_CXX_FLAGS)
+  endif()
  endif()

  if( CMAKE_SIZEOF_VOID_P EQUAL 8 AND NOT WIN32 )

... but before I just wildly commit something, I'd say this does seem 
more like a compiler bug to me and so I'd like to poll people about 
which compilers they're using to see where this appears.

FWIW, gcc 5.3.1 / ld 2.26 / gold 1.11 is what you get in Ubuntu 16.04.

Also note: This has surfaced only recently, because of how the symbol 
types evolve during the different linker stages. PassManager<Function> 
is not affected, because it is referenced in libLLVMCore.a outside the 
.o file that contains the explicit instantiation, while 
PassManager<Loop> *is* affected, because it is referenced in 
libLLVMAnalysis.a outside the .o file that contains the explicit 
instantiation, but that .cpp file including the reference does *not* 
include LoopPassManager.h where the template instantiation is declared 
extern. This somehow causes the linker to treat the two cases differently.

Thanks,
Nicolai