[cfe-dev] [Openmp-dev] libomp.lib is not automatically added on Windows

[Peyton, Jonathan L]

Clang front end developers,

We are having trouble getting the -fopenmp flag to work on Windows.  It appears that the linking phase does not include libomp.lib?  Below is an OpenMP hello world compilation output.

-- Johnny

-----Original Message-----
From: İsmail Dönmez [mailto:ismail at i10z.com] 
Sent: Monday, August 10, 2015 10:04 AM
To: Peyton, Jonathan L
Subject: Re: [Openmp-dev] libomp.lib is not automatically added on Windows

Hi,

On Mon, Aug 10, 2015 at 6:02 PM, Peyton, Jonathan L <jonathan.l.peyton at intel.com> wrote:
> Can you include -v in the compile command and post the output?

Sure:

C:\Users\ismail\Desktop>clang -O2 -fms-compatibility-version=19 -fopenmp -v omp_hello.c clang version 3.8.0 (http://llvm.org/git/clang
45770fa6e4eb618277ed85044d5a2d4c962c57cf) (http://llvm.org/git/llvm
97bdbf60d9923a9e06effbb96801129070499fd5)
Target: x86_64-pc-windows-msvc
Thread model: posix
InstalledDir: C:\Program Files\LLVM\bin
 "C:\\Program Files\\LLVM\\bin\\clang.exe" -cc1 -triple
x86_64-pc-windows-msvc19.0.0 -emit-obj -disable-free -main-file-name omp_hello.c -mrelocation-model pic -pic-level 2 -mthread-model posix -fmath-errno -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -momit-leaf-frame-pointer -v -dwarf-column-info -resource-dir "C:\\Program Files\\LLVM\\bin\\..\\lib\\clang\\3.8.0"
-internal-isystem "C:\\Program
Files\\LLVM\\bin\\..\\lib\\clang\\3.8.0\\include" -internal-isystem "C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\INCLUDE"
-internal-isystem "C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\ATLMFC\\INCLUDE" -internal-isystem "C:\\Program Files (x86)\\Windows Kits\\10\\include\\10.0.10150.0\\ucrt"
-internal-isystem "C:\\Program Files (x86)\\Windows Kits\\NETFXSDK\\4.6\\include\\um" -internal-isystem "C:\\Program Files (x86)\\Windows Kits\\8.1\\include\\shared" -internal-isystem "C:\\Program Files (x86)\\Windows Kits\\8.1\\include\\um"
-internal-isystem "C:\\Program Files (x86)\\Windows Kits\\8.1\\include\\winrt" -O2 -fdebug-compilation-dir "C:\\Users\\ismail\\Desktop" -ferror-limit 19 -fmessage-length 100 -fopenmp -fnoopenmp-use-tls -mstackrealign -fms-extensions -fms-compatibility -fms-compatibility-version=19 -fdelayed-template-parsing -fobjc-runtime=gcc -fdiagnostics-show-option -fcolor-diagnostics -vectorize-loops -vectorize-slp -o "C:\\Users\\ismail\\AppData\\Local\\Temp\\omp_hello-45bdc2.o" -x c omp_hello.c clang -cc1 version 3.8.0 based upon LLVM 3.8.0svn default target x86_64-pc-windows-msvc #include "..." search starts here:
#include <...> search starts here:
 C:\Program Files\LLVM\bin\..\lib\clang\3.8.0\include
 C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\INCLUDE  C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\ATLMFC\INCLUDE  C:\Program Files (x86)\Windows Kits\10\include\10.0.10150.0\ucrt  C:\Program Files (x86)\Windows Kits\NETFXSDK\4.6\include\um  C:\Program Files (x86)\Windows Kits\8.1\include\shared  C:\Program Files (x86)\Windows Kits\8.1\include\um  C:\Program Files (x86)\Windows Kits\8.1\include\winrt End of search list.
 "C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\bin\\amd64\\link.exe" -out:a.exe -defaultlib:libcmt -nologo "C:\\Users\\ismail\\AppData\\Local\\Temp\\omp_hello-45bdc2.o"
omp_hello-45bdc2.o : error LNK2019: unresolved external symbol __kmpc_fork_call referenced in function main omp_hello-45bdc2.o : error LNK2019: unresolved external symbol omp_get_thread_num referenced in function .omp_outlined.
omp_hello-45bdc2.o : error LNK2019: unresolved external symbol omp_get_num_threads referenced in function .omp_outlined.
omp_hello-45bdc2.o : error LNK2019: unresolved external symbol __kmpc_cancel_barrier referenced in function .omp_outlined.
a.exe : fatal error LNK1120: 4 unresolved externals
clang.exe: error: linker command failed with exit code 1120 (use -v to see invocation)

C:\Users\ismail\Desktop>