Implement a "--pgo" option for the Jupyter magic that applies profile guided...

Implement a "--pgo" option for the Jupyter magic that applies profile guided optimisation during C compilation.

CHANGES.rst

@@ -41,6 +41,11 @@ Features added
 * The gdb support for Python code (``libpython.py``) was updated to the latest
   version in CPython 3.7 (git rev 5fe59f8).
 
+* The IPython/Jupyter magic integration has a new option ``%%cython --pgo`` for profile
+  guided optimisation. It compiles the cell with PGO settings for the C compiler,
+  executes it to generate a runtime profile, and then compiles it again using that
+  profile for C compiler optimisation.  Currently only tested with gcc.
+
 * ``len(memoryview)`` can be used in nogil sections to get the size of the
   first dimension of a memory view (``shape[0]``). (Github issue #1733)
 

Cython/Build/Tests/TestIpythonMagic.py

@@ -35,6 +35,12 @@ def call(x):
     return f(*(x,))
 """)
 
+pgo_cython3_code = cython3_code + py3compat.str_to_unicode("""\
+def main():
+    for _ in range(100): call(5)
+main()
+""")
+
 
 if sys.platform == 'win32':
     # not using IPython's decorators here because they depend on "nose"
@@ -117,6 +123,13 @@ class TestIPythonMagic(CythonTest):
         self.assertEqual(ip.user_ns['g'], 2 // 10)
         self.assertEqual(ip.user_ns['h'], 2 // 10)
 
+    def test_cython3_pgo(self):
+        # The Cython cell defines the functions f() and call().
+        ip.run_cell_magic('cython', '-3 --pgo', pgo_cython3_code)
+        ip.ex('g = f(10); h = call(10); main()')
+        self.assertEqual(ip.user_ns['g'], 2.0 / 10.0)
+        self.assertEqual(ip.user_ns['h'], 2.0 / 10.0)
+
     @skip_win32('Skip on Windows')
     def test_extlibs(self):
         code = py3compat.str_to_unicode("""