Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -82,21 +82,6 @@
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-exceptions -fno-rtti")
 endif ()
 
-# Define the FLAGS for the compilation of isl and imath
-#
-# Those are the only C files we have in the repository. Hence, we can just use
-# the CFLAGS to identify them.
-#
-# We first set the visibility of all isl functions to hidden to ensure we do
-# not clash with other isl versions that got linked into a program that uses
-# Polly. (This happens e.g when linking Polly with dragonegg)
-#
-# We also disable all warnings, as these should be fixed upstream. There is
-# no value in reporting them here.
-if (NOT MSVC)
-  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fvisibility=hidden -w")
-endif ()
-
 # Add path for custom modules
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${POLLY_SOURCE_DIR}/cmake")
 
@@ -120,10 +105,7 @@
   ${CMAKE_CURRENT_SOURCE_DIR}/include
   ${CMAKE_CURRENT_SOURCE_DIR}/lib/JSON/include
   ${CMAKE_CURRENT_BINARY_DIR}/lib/External/isl/include
-  ${CMAKE_CURRENT_BINARY_DIR}/lib/External/isl
   ${CMAKE_CURRENT_SOURCE_DIR}/lib/External/isl/include
-  ${CMAKE_CURRENT_SOURCE_DIR}/lib/External/isl/imath
-  ${CMAKE_CURRENT_SOURCE_DIR}/lib/External/isl
   ${CMAKE_CURRENT_BINARY_DIR}/include
   )
 
Index: cmake/polly_macros.cmake
===================================================================
--- cmake/polly_macros.cmake
+++ cmake/polly_macros.cmake
@@ -1,6 +1,9 @@
 
+include(CMakeParseArguments)
+
 macro(add_polly_library name)
-  set(srcs ${ARGN})
+  cmake_parse_arguments(ARG "FORCE_STATIC" "" "" ${ARGN})
+  set(srcs ${ARG_UNPARSED_ARGUMENTS})
   if(MSVC_IDE OR XCODE)
     file( GLOB_RECURSE headers *.h *.td *.def)
     set(srcs ${srcs} ${headers})
@@ -12,6 +15,8 @@
   endif(MSVC_IDE OR XCODE)
   if (MODULE)
     set(libkind MODULE)
+  elseif (ARG_FORCE_STATIC)
+    set(libkind STATIC)
   elseif (SHARED_LIBRARY)
     set(libkind SHARED)
   else()
Index: lib/CMakeLists.txt
===================================================================
--- lib/CMakeLists.txt
+++ lib/CMakeLists.txt
@@ -16,256 +16,8 @@
   set (GPGPU_CODEGEN_FILES)
 endif (GPU_CODEGEN)
 
-
-# External: Integer Set Library
-set(ISL_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/External/isl")
-set(ISL_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}/External/isl")
-
-# Determine version of isl
-if (EXISTS "${ISL_SOURCE_DIR}/GIT_HEAD_ID")
-  # The source comes from a 'make dist' archive
-  file(READ "${ISL_SOURCE_DIR}/GIT_HEAD_ID" GIT_HEAD_ID)
-  string(STRIP "${GIT_HEAD_ID}" GIT_HEAD_ID)
-elseif (EXISTS "${ISL_SOURCE_DIR}/gitversion.h")
-  # The source directory is preconfigured
-  file(READ "${ISL_SOURCE_DIR}/gitversion.h" GITVERSION_H)
-  string(REGEX REPLACE ".*\\\"([^\\\"]*)\\\".*" "\\1" GIT_HEAD_ID "${GITVERSION_H}")
-elseif ()
-  # Unknown revision
-  # TODO: We could look for a .git and get the revision from HEAD
-  set(GIT_HEAD_ID "UNKNOWN")
-endif ()
-
-message(STATUS "ISL version: ${GIT_HEAD_ID}")
-
-# Enable small integer optimization and imath
-set(USE_GMP_FOR_MP OFF)
-set(USE_IMATH_FOR_MP ON)
-set(USE_SMALL_INT_OPT ON)
-
-# Determine compiler characteristics
-include(CheckCSourceCompiles)
-
-# Like check_c_source_compiles, but sets the result to either
-# 0 (error while compiling) or 1 (compiled successfully)
-# Required for compatibility with autotool's AC_CHECK_DECLS
-function (check_c_source_compiles_numeric _prog _var)
-  check_c_source_compiles("${_prog}" "${_var}")
-  if ("${${_var}}")
-    set("${_var}" 1 PARENT_SCOPE)
-  else ()
-    set("${_var}" 0 PARENT_SCOPE)
-  endif ()
-endfunction ()
-
-# Check for the existance of a type
-function (check_c_type_exists _type _files _variable)
-  set(_includes "")
-  foreach (file_name ${_files})
-     set(_includes "${_includes}#include<${file_name}>\n")
-  endforeach()
-  check_c_source_compiles("
-    ${_includes}
-    ${_type} typeVar;
-    int main() {
-        return 0;
-    }
-    " ${_variable})
-endfunction ()
-
-
-check_c_source_compiles("
-  int func(void) __attribute__((__warn_unused_result__));
-  int main() { return 0; }
-  " HAS_ATTRIBUTE_WARN_UNUSED_RESULT)
-set(GCC_WARN_UNUSED_RESULT)
-if (HAS_ATTRIBUTE_WARN_UNUSED_RESULT)
-  set(GCC_WARN_UNUSED_RESULT "__attribute__((__warn_unused_result__))")
-endif ()
-
-check_c_source_compiles("
-  static void foo(void) __attribute__ ((unused));
-  int main() { return 0; }
-  " HAVE___ATTRIBUTE__)
-
-
-check_c_source_compiles_numeric("
-  #include <strings.h>
-  int main() { ffs(0); return 0; }
-  " HAVE_DECL_FFS)
-
-check_c_source_compiles_numeric("
-  int main() { __builtin_ffs(0); return 0; }
-  " HAVE_DECL___BUILTIN_FFS)
-
-check_c_source_compiles_numeric("
-  #include <intrin.h>
-  int main() { _BitScanForward(NULL, 0); return 0; }
-  " HAVE_DECL__BITSCANFORWARD)
-
-if (NOT HAVE_DECL_FFS AND
-    NOT HAVE_DECL___BUILTIN_FFS AND
-    NOT HAVE_DECL__BITSCANFORWARD)
-  message(FATAL_ERROR "No ffs implementation found")
-endif ()
-
-
-check_c_source_compiles_numeric("
-  #include <strings.h>
-  int main() { strcasecmp(\"\", \"\"); return 0; }
-  " HAVE_DECL_STRCASECMP)
-
-check_c_source_compiles_numeric("
-  #include <string.h>
-  int main() { _stricmp(\"\", \"\"); return 0; }
-  " HAVE_DECL__STRICMP)
-
-if (NOT HAVE_DECL_STRCASECMP AND NOT HAVE_DECL__STRICMP)
-  message(FATAL_ERROR "No strcasecmp implementation found")
-endif ()
-
-
-check_c_source_compiles_numeric("
-  #include <strings.h>
-  int main() { strncasecmp(\"\", \"\", 0); return 0; }
-  " HAVE_DECL_STRNCASECMP)
-
-check_c_source_compiles_numeric("
-  #include <string.h>
-  int main() { _strnicmp(\"\", \"\", 0); return 0; }
-  " HAVE_DECL__STRNICMP)
-
-if (NOT HAVE_DECL_STRNCASECMP AND NOT HAVE_DECL__STRNICMP)
-  message(FATAL_ERROR "No strncasecmp implementation found")
-endif ()
-
-
-check_c_source_compiles_numeric("
-  #include <stdio.h>
-  int main() { snprintf((void*)0, 0, \"\"); return 0; }
-  " HAVE_DECL_SNPRINTF)
-
-check_c_source_compiles_numeric("
-  #include <stdio.h>
-  int main() { _snprintf((void*)0, 0, \"\"); return 0; }
-  " HAVE_DECL__SNPRINTF)
-
-if (NOT HAVE_DECL_SNPRINTF AND NOT HAVE_DECL__SNPRINTF)
-  message(FATAL_ERROR "No snprintf implementation found")
-endif ()
-
-
-check_c_type_exists(uint8_t "" HAVE_UINT8T)
-check_c_type_exists(uint8_t "stdint.h" HAVE_STDINT_H)
-check_c_type_exists(uint8_t "inttypes.h" HAVE_INTTYPES_H)
-check_c_type_exists(uint8_t "sys/types.h" HAVE_SYS_INTTYPES_H)
-if (HAVE_UINT8T)
-  set(INCLUDE_STDINT_H "")
-elseif (HAVE_STDINT_H)
-  set(INCLUDE_STDINT_H "#include <stdint.h>")
-elseif (HAVE_INTTYPES_H)
-  set(INCLUDE_STDINT_H "#include <inttypes.h>")
-elseif (HAVE_SYS_INTTYPES_H)
-  set(INCLUDE_STDINT_H "#include <sys/inttypes.h>")
-else ()
-  message(FATAL_ERROR "No stdint.h or compatible found")
-endif ()
-
-# Write configure result
-# configure_file(... COPYONLY) avoids that the time stamp changes if the file is identical
-file(WRITE "${ISL_BINARY_DIR}/gitversion.h.tmp"
-     "#define GIT_HEAD_ID \"${GIT_HEAD_ID}\"")
-configure_file("${ISL_BINARY_DIR}/gitversion.h.tmp"
-               "${ISL_BINARY_DIR}/gitversion.h" COPYONLY)
-
-file(WRITE "${ISL_BINARY_DIR}/include/isl/stdint.h.tmp"
-     "${INCLUDE_STDINT_H}")
-configure_file("${ISL_BINARY_DIR}/include/isl/stdint.h.tmp"
-               "${ISL_BINARY_DIR}/include/isl/stdint.h" COPYONLY)
-
-configure_file("External/isl_config.h.cmake" "${ISL_BINARY_DIR}/isl_config.h")
-
-
-# ISL files to compile
-set (ISL_FILES
-    External/isl/basis_reduction_tab.c
-    External/isl/isl_aff.c
-    External/isl/isl_affine_hull.c
-    External/isl/isl_arg.c
-    External/isl/isl_ast_build.c
-    External/isl/isl_ast_build_expr.c
-    External/isl/isl_ast.c
-    External/isl/isl_ast_codegen.c
-    External/isl/isl_ast_graft.c
-    External/isl/isl_band.c
-    External/isl/isl_bernstein.c
-    External/isl/isl_blk.c
-    External/isl/isl_bound.c
-    External/isl/isl_coalesce.c
-    External/isl/isl_constraint.c
-    External/isl/isl_convex_hull.c
-    External/isl/isl_ctx.c
-    External/isl/isl_deprecated.c
-    External/isl/isl_dim_map.c
-    External/isl/isl_equalities.c
-    External/isl/isl_factorization.c
-    External/isl/isl_farkas.c
-    External/isl/isl_ffs.c
-    External/isl/isl_flow.c
-    External/isl/isl_fold.c
-    External/isl/isl_hash.c
-    External/isl/isl_id.c
-    External/isl/isl_id_to_ast_expr.c
-    External/isl/isl_id_to_pw_aff.c
-    External/isl/isl_ilp.c
-    External/isl/isl_imath.c
-    External/isl/isl_input.c
-    External/isl/isl_int_sioimath.c
-    External/isl/isl_local_space.c
-    External/isl/isl_lp.c
-    External/isl/isl_map.c
-    External/isl/isl_map_list.c
-    External/isl/isl_map_simplify.c
-    External/isl/isl_map_subtract.c
-    External/isl/isl_map_to_basic_set.c
-    External/isl/isl_mat.c
-    External/isl/isl_morph.c
-    External/isl/isl_obj.c
-    External/isl/isl_options.c
-    External/isl/isl_output.c
-    External/isl/isl_point.c
-    External/isl/isl_polynomial.c
-    External/isl/isl_printer.c
-    External/isl/isl_range.c
-    External/isl/isl_reordering.c
-    External/isl/isl_sample.c
-    External/isl/isl_scan.c
-    External/isl/isl_schedule.c
-    External/isl/isl_schedule_band.c
-    External/isl/isl_schedule_node.c
-    External/isl/isl_schedule_read.c
-    External/isl/isl_schedule_tree.c
-    External/isl/isl_scheduler.c
-    External/isl/isl_seq.c
-    External/isl/isl_set_list.c
-    External/isl/isl_sort.c
-    External/isl/isl_space.c
-    External/isl/isl_stream.c
-    External/isl/isl_tab.c
-    External/isl/isl_tab_pip.c
-    External/isl/isl_tarjan.c
-    External/isl/isl_transitive_closure.c
-    External/isl/isl_union_map.c
-    External/isl/isl_val.c
-    External/isl/isl_val_sioimath.c
-    External/isl/isl_vec.c
-    External/isl/isl_version.c
-    External/isl/isl_vertices.c
-    External/isl/print.c
-    External/isl/imath/gmp_compat.c
-    External/isl/imath/imath.c
-    External/isl/imath/imrat.c
-    )
+# Compile ISL into a separate library.
+add_subdirectory(External)
 
 set(POLLY_HEADER_FILES)
 if (MSVC_IDE OR XCODE)
@@ -299,12 +51,10 @@
   Transform/DeadCodeElimination.cpp
   Transform/IndependentBlocks.cpp
   Transform/ScheduleOptimizer.cpp
-  ${ISL_FILES}
   ${POLLY_HEADER_FILES}
   )
 
-# ISL requires at least C99 to compile. gcc < 5.0 use -std=gnu89 as default.
-target_enable_c99(Polly)
+target_link_libraries(Polly Polly_isl)
 
 if (BUILD_SHARED_LIBS)
   target_link_libraries(Polly
Index: lib/External/CMakeLists.txt
===================================================================
--- /dev/null
+++ lib/External/CMakeLists.txt
@@ -0,0 +1,276 @@
+# External: Integer Set Library
+set(ISL_SOURCE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/isl")
+set(ISL_BINARY_DIR "${CMAKE_CURRENT_BINARY_DIR}/isl")
+
+# Determine version of isl
+if (EXISTS "${ISL_SOURCE_DIR}/GIT_HEAD_ID")
+  # The source comes from a 'make dist' archive
+  file(READ "${ISL_SOURCE_DIR}/GIT_HEAD_ID" GIT_HEAD_ID)
+  string(STRIP "${GIT_HEAD_ID}" GIT_HEAD_ID)
+elseif (EXISTS "${ISL_SOURCE_DIR}/gitversion.h")
+  # The source directory is preconfigured
+  file(READ "${ISL_SOURCE_DIR}/gitversion.h" GITVERSION_H)
+  string(REGEX REPLACE ".*\\\"([^\\\"]*)\\\".*" "\\1" GIT_HEAD_ID "${GITVERSION_H}")
+elseif ()
+  # Unknown revision
+  # TODO: We could look for a .git and get the revision from HEAD
+  set(GIT_HEAD_ID "UNKNOWN")
+endif ()
+
+message(STATUS "ISL version: ${GIT_HEAD_ID}")
+
+# Enable small integer optimization and imath
+set(USE_GMP_FOR_MP OFF)
+set(USE_IMATH_FOR_MP ON)
+set(USE_SMALL_INT_OPT ON)
+
+# Determine compiler characteristics
+include(CheckCSourceCompiles)
+
+# Like check_c_source_compiles, but sets the result to either
+# 0 (error while compiling) or 1 (compiled successfully)
+# Required for compatibility with autotool's AC_CHECK_DECLS
+function (check_c_source_compiles_numeric _prog _var)
+  check_c_source_compiles("${_prog}" "${_var}")
+  if ("${${_var}}")
+    set("${_var}" 1 PARENT_SCOPE)
+  else ()
+    set("${_var}" 0 PARENT_SCOPE)
+  endif ()
+endfunction ()
+
+# Check for the existance of a type
+function (check_c_type_exists _type _files _variable)
+  set(_includes "")
+  foreach (file_name ${_files})
+     set(_includes "${_includes}#include<${file_name}>\n")
+  endforeach()
+  check_c_source_compiles("
+    ${_includes}
+    ${_type} typeVar;
+    int main() {
+        return 0;
+    }
+    " ${_variable})
+endfunction ()
+
+
+check_c_source_compiles("
+  int func(void) __attribute__((__warn_unused_result__));
+  int main() { return 0; }
+  " HAS_ATTRIBUTE_WARN_UNUSED_RESULT)
+set(GCC_WARN_UNUSED_RESULT)
+if (HAS_ATTRIBUTE_WARN_UNUSED_RESULT)
+  set(GCC_WARN_UNUSED_RESULT "__attribute__((__warn_unused_result__))")
+endif ()
+
+check_c_source_compiles("
+  static void foo(void) __attribute__ ((unused));
+  int main() { return 0; }
+  " HAVE___ATTRIBUTE__)
+
+
+check_c_source_compiles_numeric("
+  #include <strings.h>
+  int main() { ffs(0); return 0; }
+  " HAVE_DECL_FFS)
+
+check_c_source_compiles_numeric("
+  int main() { __builtin_ffs(0); return 0; }
+  " HAVE_DECL___BUILTIN_FFS)
+
+check_c_source_compiles_numeric("
+  #include <intrin.h>
+  int main() { _BitScanForward(NULL, 0); return 0; }
+  " HAVE_DECL__BITSCANFORWARD)
+
+if (NOT HAVE_DECL_FFS AND
+    NOT HAVE_DECL___BUILTIN_FFS AND
+    NOT HAVE_DECL__BITSCANFORWARD)
+  message(FATAL_ERROR "No ffs implementation found")
+endif ()
+
+
+check_c_source_compiles_numeric("
+  #include <strings.h>
+  int main() { strcasecmp(\"\", \"\"); return 0; }
+  " HAVE_DECL_STRCASECMP)
+
+check_c_source_compiles_numeric("
+  #include <string.h>
+  int main() { _stricmp(\"\", \"\"); return 0; }
+  " HAVE_DECL__STRICMP)
+
+if (NOT HAVE_DECL_STRCASECMP AND NOT HAVE_DECL__STRICMP)
+  message(FATAL_ERROR "No strcasecmp implementation found")
+endif ()
+
+
+check_c_source_compiles_numeric("
+  #include <strings.h>
+  int main() { strncasecmp(\"\", \"\", 0); return 0; }
+  " HAVE_DECL_STRNCASECMP)
+
+check_c_source_compiles_numeric("
+  #include <string.h>
+  int main() { _strnicmp(\"\", \"\", 0); return 0; }
+  " HAVE_DECL__STRNICMP)
+
+if (NOT HAVE_DECL_STRNCASECMP AND NOT HAVE_DECL__STRNICMP)
+  message(FATAL_ERROR "No strncasecmp implementation found")
+endif ()
+
+
+check_c_source_compiles_numeric("
+  #include <stdio.h>
+  int main() { snprintf((void*)0, 0, \"\"); return 0; }
+  " HAVE_DECL_SNPRINTF)
+
+check_c_source_compiles_numeric("
+  #include <stdio.h>
+  int main() { _snprintf((void*)0, 0, \"\"); return 0; }
+  " HAVE_DECL__SNPRINTF)
+
+if (NOT HAVE_DECL_SNPRINTF AND NOT HAVE_DECL__SNPRINTF)
+  message(FATAL_ERROR "No snprintf implementation found")
+endif ()
+
+
+check_c_type_exists(uint8_t "" HAVE_UINT8T)
+check_c_type_exists(uint8_t "stdint.h" HAVE_STDINT_H)
+check_c_type_exists(uint8_t "inttypes.h" HAVE_INTTYPES_H)
+check_c_type_exists(uint8_t "sys/types.h" HAVE_SYS_INTTYPES_H)
+if (HAVE_UINT8T)
+  set(INCLUDE_STDINT_H "")
+elseif (HAVE_STDINT_H)
+  set(INCLUDE_STDINT_H "#include <stdint.h>")
+elseif (HAVE_INTTYPES_H)
+  set(INCLUDE_STDINT_H "#include <inttypes.h>")
+elseif (HAVE_SYS_INTTYPES_H)
+  set(INCLUDE_STDINT_H "#include <sys/inttypes.h>")
+else ()
+  message(FATAL_ERROR "No stdint.h or compatible found")
+endif ()
+
+# Write configure result
+# configure_file(... COPYONLY) avoids that the time stamp changes if the file is identical
+file(WRITE "${ISL_BINARY_DIR}/gitversion.h.tmp"
+     "#define GIT_HEAD_ID \"${GIT_HEAD_ID}\"")
+configure_file("${ISL_BINARY_DIR}/gitversion.h.tmp"
+               "${ISL_BINARY_DIR}/gitversion.h" COPYONLY)
+
+file(WRITE "${ISL_BINARY_DIR}/include/isl/stdint.h.tmp"
+     "${INCLUDE_STDINT_H}")
+configure_file("${ISL_BINARY_DIR}/include/isl/stdint.h.tmp"
+               "${ISL_BINARY_DIR}/include/isl/stdint.h" COPYONLY)
+
+configure_file("isl_config.h.cmake" "${ISL_BINARY_DIR}/isl_config.h")
+
+include_directories(BEFORE
+  ${ISL_BINARY_DIR}
+  ${ISL_SOURCE_DIR}/imath
+  ${ISL_SOURCE_DIR}/include
+  ${ISL_SOURCE_DIR}
+)
+
+# ISL files to compile
+set (ISL_FILES
+    isl/basis_reduction_tab.c
+    isl/isl_aff.c
+    isl/isl_affine_hull.c
+    isl/isl_arg.c
+    isl/isl_ast_build.c
+    isl/isl_ast_build_expr.c
+    isl/isl_ast.c
+    isl/isl_ast_codegen.c
+    isl/isl_ast_graft.c
+    isl/isl_band.c
+    isl/isl_bernstein.c
+    isl/isl_blk.c
+    isl/isl_bound.c
+    isl/isl_coalesce.c
+    isl/isl_constraint.c
+    isl/isl_convex_hull.c
+    isl/isl_ctx.c
+    isl/isl_deprecated.c
+    isl/isl_dim_map.c
+    isl/isl_equalities.c
+    isl/isl_factorization.c
+    isl/isl_farkas.c
+    isl/isl_ffs.c
+    isl/isl_flow.c
+    isl/isl_fold.c
+    isl/isl_hash.c
+    isl/isl_id.c
+    isl/isl_id_to_ast_expr.c
+    isl/isl_id_to_pw_aff.c
+    isl/isl_ilp.c
+    isl/isl_imath.c
+    isl/isl_input.c
+    isl/isl_int_sioimath.c
+    isl/isl_local_space.c
+    isl/isl_lp.c
+    isl/isl_map.c
+    isl/isl_map_list.c
+    isl/isl_map_simplify.c
+    isl/isl_map_subtract.c
+    isl/isl_map_to_basic_set.c
+    isl/isl_mat.c
+    isl/isl_morph.c
+    isl/isl_obj.c
+    isl/isl_options.c
+    isl/isl_output.c
+    isl/isl_point.c
+    isl/isl_polynomial.c
+    isl/isl_printer.c
+    isl/isl_range.c
+    isl/isl_reordering.c
+    isl/isl_sample.c
+    isl/isl_scan.c
+    isl/isl_schedule.c
+    isl/isl_schedule_band.c
+    isl/isl_schedule_node.c
+    isl/isl_schedule_read.c
+    isl/isl_schedule_tree.c
+    isl/isl_scheduler.c
+    isl/isl_seq.c
+    isl/isl_set_list.c
+    isl/isl_sort.c
+    isl/isl_space.c
+    isl/isl_stream.c
+    isl/isl_tab.c
+    isl/isl_tab_pip.c
+    isl/isl_tarjan.c
+    isl/isl_transitive_closure.c
+    isl/isl_union_map.c
+    isl/isl_val.c
+    isl/isl_val_sioimath.c
+    isl/isl_vec.c
+    isl/isl_version.c
+    isl/isl_vertices.c
+    isl/print.c
+    isl/imath/gmp_compat.c
+    isl/imath/imath.c
+    isl/imath/imrat.c
+    )
+
+add_polly_library(Polly_isl FORCE_STATIC
+  ${ISL_FILES}
+)
+
+# ISL requires at least C99 to compile. gcc < 5.0 use -std=gnu89 as default.
+target_enable_c99(Polly_isl)
+
+# Define the FLAGS for the compilation of isl and imath
+#
+# We first set the visibility of all isl functions to hidden to ensure we do
+# not clash with other isl versions that got linked into a program that uses
+# Polly. (This happens e.g when linking Polly with dragonegg)
+#
+# This is the reason for the FORCE_STATIC flag above; without it, not even Polly
+# could access ISL's symbols in shared library builds.
+if (NOT MSVC)
+  set_target_properties(Polly_isl PROPERTIES
+    COMPILE_FLAGS "-fvisibility=hidden -w"
+  )
+endif ()