[cfe-dev] CMAKE_INSTALL_PREFIX vs -fopenmp and clang search library search path

[Jack Howarth]

    I believe we have a gap in clang's library search path with the
enabling of the openmp support via the proposed patch at...

http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20150511/129075.html

Currently, in tree cmake builds of the openmp library using
-DCMAKE_INSTALL_PREFIX to install the llvm build in a buried
subdirectory will place the libiomp5.dylib shared library in a
directory outside of the library search path used by clang...

% clang-3.7 -fopenmp -o omp_getEnvInfo omp_getEnvInfo.c -v
clang version 3.7.0 (trunk)
Target: x86_64-apple-darwin14.4.0
Thread model: posix
 "/sw/opt/llvm-3.7.0/bin/clang-3.7" -cc1 -triple
x86_64-apple-macosx10.10.0 -emit-obj -mrelax-all -disable-free
-disable-llvm-verifier -main-file-name omp_getEnvInfo.c
-mrelocation-model pic -pic-level 2 -mthread-model posix
-mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2
-target-linker-version 242 -v -dwarf-column-info
-fno-unique-section-names -resource-dir
/sw/opt/llvm-3.7.0/bin/../lib/clang/3.7.0 -fdebug-compilation-dir
/Users/howarth/openmp_examples -ferror-limit 19 -fmessage-length 140
-fopenmp -stack-protector 1 -mstackrealign -fblocks
-fobjc-runtime=macosx-10.10.0 -fencode-extended-block-signature
-fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o
/var/folders/1l/n78sywl52lz6kkys6nv7mnph0000gp/T/omp_getEnvInfo-e20595.o
-x c omp_getEnvInfo.c
clang -cc1 version 3.7.0 based upon LLVM 3.7.0svn default target
x86_64-apple-darwin14.4.0
ignoring nonexistent directory "/usr/local/include"
#include "..." search starts here:
#include <...> search starts here:
 /sw/opt/llvm-3.7.0/bin/../lib/clang/3.7.0/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.
 "/sw/opt/llvm-3.7.0/bin/ld" -demangle -dynamic -arch x86_64
-macosx_version_min 10.10.0 -o omp_getEnvInfo -liomp5
/var/folders/1l/n78sywl52lz6kkys6nv7mnph0000gp/T/omp_getEnvInfo-e20595.o
-lSystem
ld: library not found for -liomp5
clang-3.7: error: linker command failed with exit code 1 (use -v to
see invocation)

requiring an explicit path to passed to the compiler...

% clang-3.7 -fopenmp -L/sw/opt/llvm-3.7.0/lib -o omp_getEnvInfo omp_getEnvInfo.c
% otool -L ./omp_getEnvInfo
./omp_getEnvInfo:
/sw/opt/llvm-3.7.0/lib/libiomp5.dylib (compatibility version 5.0.0,
current version 5.0.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current
version 1213.0.0)

Currently, all the other shared libraries linked by the clang
compilers (aside from libc++) are expected to be located in the
clang/3.7.0/lib/darwin subdirectory (such as
libclang_rt.asan_iossim_dynamic.dylib and
libclang_rt.asan_osx_dynamic.dylib). Using CMAKE_INSTALL_PREFIX in the
cmake build to bury the llvm installation has no impact on the usage
of those two libraries with the -fsanitize flags but the current
search library search path doesn't do the same for the libiomp5
relocation in the same case.
            Jack