Backport of https://github.com/pypa/pip/pull/9827 with parts of
https://github.com/pypa/pip/pull/4690 to make it work with pip v9.0.1
diff --git a/pip/vcs/git.py b/pip/vcs/git.py
index 2187dd8..d1502f8 100644
--- a/pip/vcs/git.py
+++ b/pip/vcs/git.py
@@ -81,7 +81,7 @@ class Git(VersionControl):
         and branches may need origin/ as a prefix.
         Returns the SHA1 of the branch or tag if found.
         """
-        revisions = self.get_short_refs(dest)
+        revisions = self.get_short_refs(dest, rev)
 
         origin_rev = 'origin/%s' % rev
         if origin_rev in revisions:
@@ -171,12 +171,20 @@ class Git(VersionControl):
             ['rev-parse', 'HEAD'], show_stdout=False, cwd=location)
         return current_rev.strip()
 
-    def get_full_refs(self, location):
+    def get_full_refs(self, location, pattern=''):
         """Yields tuples of (commit, ref) for branches and tags"""
-        output = self.run_command(['show-ref'],
+        output = self.run_command(['show-ref', pattern],
                                   show_stdout=False, cwd=location)
-        for line in output.strip().splitlines():
-            commit, ref = line.split(' ', 1)
+        for line in output.split("\n"):
+            line = line.rstrip("\r")
+            if not line:
+                continue
+            try:
+                commit, ref = line.split(' ', 1)
+            except ValueError:
+                # Include the offending line to simplify troubleshooting if
+                # this error ever occurs.
+                raise ValueError(f'unexpected show-ref line: {line!r}')
             yield commit.strip(), ref.strip()
 
     def is_ref_remote(self, ref):
@@ -200,10 +208,10 @@ class Git(VersionControl):
     def get_refs(self, location):
         return self.get_short_refs(location)
 
-    def get_short_refs(self, location):
+    def get_short_refs(self, location, pattern=''):
         """Return map of named refs (branches or tags) to commit hashes."""
         rv = {}
-        for commit, ref in self.get_full_refs(location):
+        for commit, ref in self.get_full_refs(location, pattern):
             ref_name = None
             if self.is_ref_remote(ref):
                 ref_name = ref[len('refs/remotes/'):]