[libcxx] Allow the use of ccache when running the test suite.

Summary:
In order to get the bots running quicker I would like to be able to use ccache 
with the test suite. This patch adds support for running the test suite using 
ccache. To use ccache pass `--param=use_ccache=true` when running the test suite.

ccache will not cache any command that invokes ld, so the build step needs to be
split into two separate compile commands. The cost of splitting the build step
into two parts when not using ccache seems to be minimal. On my machine I saw a
difference of ~5 seconds on a 5 minute test suite run.

A full test suite run with ccache generates about 250MB of cached data.

I recorded the following times for running the test suite in the following configurations:
- no ccache: 340s
- initial ccache run: 380s
- rerun with ccache (no changes): 53s.
- rerun with ccache (<string> changed): 80s
- rerun with ccache (<cmath> changed): 169s
- rerun with ccache (<valarray> changed): 69s





Reviewers: mclow.lists, jroelofs, danalbert

Reviewed By: jroelofs

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D6647

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@224603 91177308-0d34-0410-b5e6-96231b3b80d8

test/lit.cfg

@@ -29,12 +29,14 @@ class LibcxxTestFormat(lit.formats.FileBasedTest):
     """
 
     def __init__(self, cxx_under_test, use_verify_for_fail,
-                 cpp_flags, ld_flags, exec_env):
+                 cpp_flags, ld_flags, exec_env,
+                 use_ccache=False):
         self.cxx_under_test = cxx_under_test
         self.use_verify_for_fail = use_verify_for_fail
         self.cpp_flags = list(cpp_flags)
         self.ld_flags = list(ld_flags)
         self.exec_env = dict(exec_env)
+        self.use_ccache = use_ccache
 
     def execute(self, test, lit_config):
         while True:
@@ -100,20 +102,44 @@ class LibcxxTestFormat(lit.formats.FileBasedTest):
         report += '\n'
         return cmd, report, rc
 
-    def _build(self, exec_path, source_path, compile_only=False,
-               use_verify=False):
-        cmd = [self.cxx_under_test, '-o', exec_path,
-               source_path] + self.cpp_flags
-
-        if compile_only:
-            cmd += ['-c']
-        else:
-            cmd += self.ld_flags
-
+    def _compile(self, output_path, source_path, use_verify=False):
+        cmd = [self.cxx_under_test, '-c', '-o', output_path, source_path]
+        cmd += self.cpp_flags
         if use_verify:
             cmd += ['-Xclang', '-verify']
-
+        if self.use_ccache:
+            cmd = ['ccache'] + cmd
         out, err, rc = lit.util.executeCommand(cmd)
+        return cmd, out, err, rc
+
+    def _link(self, exec_path, object_path):
+        cmd = [self.cxx_under_test, '-o', exec_path, object_path]
+        cmd += self.cpp_flags + self.ld_flags
+        out, err, rc = lit.util.executeCommand(cmd)
+        return cmd, out, err, rc
+
+    def _compile_and_link(self, exec_path, source_path):
+        object_file = tempfile.NamedTemporaryFile(suffix=".o", delete=False)
+        object_path = object_file.name
+        object_file.close()
+        try:
+            cmd, out, err, rc = self._compile(object_path, source_path)
+            if rc != 0:
+                return cmd, out, err, rc
+            return self._link(exec_path, object_path)
+        finally:
+            try:
+                os.remove(object_path)
+            except:
+                pass
+
+    def _build(self, exec_path, source_path, compile_only=False,
+               use_verify=False):
+        if compile_only:
+            cmd, out, err, rc = self._compile(exec_path, source_path, use_verify)
+        else:
+            assert not use_verify
+            cmd, out, err, rc = self._compile_and_link(exec_path, source_path)
         return self._make_report(cmd, out, err, rc)
 
     def _clean(self, exec_path):
@@ -190,6 +216,7 @@ class Configuration(object):
         self.link_flags = ['-nodefaultlibs']
         self.use_system_lib = False
         self.use_clang_verify = False
+        self.use_ccache = False
 
         if platform.system() not in ('Darwin', 'FreeBSD', 'Linux'):
             self.lit_config.fatal("unrecognized system")
@@ -221,6 +248,7 @@ class Configuration(object):
         self.configure_obj_root()
         self.configure_use_system_lib()
         self.configure_use_clang_verify()
+        self.configure_ccache()
         self.configure_env()
         self.configure_std_flag()
         self.configure_compile_flags()
@@ -240,7 +268,8 @@ class Configuration(object):
             self.use_clang_verify,
             cpp_flags=self.compile_flags,
             ld_flags=self.link_flags,
-            exec_env=self.env)
+            exec_env=self.env,
+            use_ccache=self.use_ccache)
 
     def configure_cxx(self):
         # Gather various compiler parameters.
@@ -325,6 +354,11 @@ class Configuration(object):
             self.lit_config.note(
                 "inferred use_clang_verify as: %r" % self.use_clang_verify)
 
+    def configure_ccache(self):
+        self.use_ccache = self.get_lit_bool('use_ccache', False)
+        if self.use_ccache:
+            self.lit_config.note('enabling ccache')
+
     def configure_features(self):
         additional_features = self.get_lit_conf('additional_features')
         if additional_features: