Add graph references

references/igraph-1.0.1/etc/cmake/lto.cmake

@@ -0,0 +1,23 @@
+include(helpers)
+
+tristate(IGRAPH_ENABLE_LTO "Enable link-time optimization" OFF)
+
+include(CheckIPOSupported)
+
+if(IGRAPH_ENABLE_LTO)
+  # this matches both ON and AUTO
+  check_ipo_supported(RESULT IPO_SUPPORTED OUTPUT IPO_NOT_SUPPORTED_REASON)
+  if(IGRAPH_ENABLE_LTO STREQUAL "AUTO")
+    # autodetection
+    set(IGRAPH_ENABLE_LTO ${IPO_SUPPORTED})
+    if(IPO_SUPPORTED)
+      set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+    endif()
+  elseif(IPO_SUPPORTED)
+    # user wanted LTO and the compiler supports it
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
+  else()
+    # user wanted LTO and the compiler does not support it
+    message(FATAL_ERROR "Link-time optimization not supported on this compiler")
+  endif()
+endif()