Fix default blas flag detection by reworking try_blas_flag.

theano/tensor/blas.py

@@ -289,8 +289,9 @@ SOMEPATH/Canopy_64bit/User/lib/python2.7/site-packages/numpy/distutils/system_in
                 flags += ['-l%s' % l for l in ["mkl_core",
                                                "mkl_intel_thread",
                                                "mkl_rt"]]
-                if try_blas_flag(flags):
-                    return ' '.join(flags)
+                res = try_blas_flag(flags)
+                if res:
+                    return res
 
         ret = (
             # TODO: the Gemm op below should separate the
@@ -301,8 +302,10 @@ SOMEPATH/Canopy_64bit/User/lib/python2.7/site-packages/numpy/distutils/system_in
             ['-L%s' % l for l in blas_info.get('library_dirs', [])] +
             ['-l%s' % l for l in blas_info.get('libraries', [])] +
             blas_info.get('extra_link_args', []))
-        if try_blas_flag(ret):
-            return ' '.join(ret)
+        res = try_blas_flag(ret)
+        if res:
+            return res
+
         # Try to add the anaconda lib directory to runtime loading of lib.
         # This fix some case with Anaconda 2.3 on Linux.
         # Newer Anaconda still have this problem but only have
@@ -311,8 +314,9 @@ SOMEPATH/Canopy_64bit/User/lib/python2.7/site-packages/numpy/distutils/system_in
             and "linux" in sys.platform):
             lib_path = os.path.join(sys.prefix, 'lib')
             ret.append('-Wl,-rpath,' + lib_path)
-            if try_blas_flag(ret):
-                return ' '.join(ret)
+            res = try_blas_flag(ret)
+            if res:
+                return res
 
     except KeyError:
         pass
@@ -322,9 +326,7 @@ SOMEPATH/Canopy_64bit/User/lib/python2.7/site-packages/numpy/distutils/system_in
     # readily available. We try to see if that's the case, rather
     # than disable blas. To test it correctly, we must load a program.
     # Otherwise, there could be problem in the LD_LIBRARY_PATH.
-    ret = try_blas_flag(['-lblas'])
-    if ret:
-        return ' '.join(ret)
+    return try_blas_flag(['-lblas'])
 
 
 def try_blas_flag(flags):
@@ -344,15 +346,21 @@ def try_blas_flag(flags):
             return 0;
         }
         """)
-    flags.extend('-L' + d for d in theano.gof.cmodule.std_lib_dirs())
     res = GCC_compiler.try_compile_tmp(
         test_code, tmp_prefix='try_blas_',
         flags=flags, try_run=True)
     # res[0]: shows successful compilation
     # res[1]: shows successful execution
     if res and res[0] and res[1]:
-        return flags
+        return ' '.join(flags)
     else:
+        # Retry adding '-L' flags which may be required
+        flags = flags + ['-L' + d for d in theano.gof.cmodule.std_lib_dirs()]
+        res = GCC_compiler.try_compile_tmp(
+            test_code, tmp_prefix='try_blas_',
+            flags=flags, try_run=True)
+        if res and res[0] and res[1]:
+            return ' '.join(flags)
         return ""