[NFC] Prefer subprocess.DEVNULL over os.devnull (#106500)

There is no need to support Python 2.7 anymore, Python 3.3+ has
`subprocess.DEVNULL`. This is good practice and also prevents file
handles from
staying open unnecessarily.

Also remove a couple unused or unneeded `__future__` imports.

3 files changed, 10 insertions, 23 deletions

diff --git a/llvm/utils/UpdateTestChecks/common.py b/llvm/utils/UpdateTestChecks/common.py
index c5e4ad4..9b9be69 100644
--- a/llvm/utils/UpdateTestChecks/common.py
+++ b/llvm/utils/UpdateTestChecks/common.py
@@ -1,11 +1,8 @@
-from __future__ import print_function
-
 import argparse
 import bisect
 import collections
 import copy
 import glob
-import itertools
 import os
 import re
 import subprocess
@@ -517,12 +514,13 @@ def invoke_tool(exe, cmd_args, ir, preprocess_cmd=None, verbose=False):
                     sep="",
                     file=sys.stderr,
                 )
-            # Python 2.7 doesn't have subprocess.DEVNULL:
-            with open(os.devnull, "w") as devnull:
-                pp = subprocess.Popen(
-                    preprocess_cmd, shell=True, stdin=devnull, stdout=subprocess.PIPE
-                )
-                ir_file = pp.stdout
+            pp = subprocess.Popen(
+                preprocess_cmd,
+                shell=True,
+                stdin=subprocess.DEVNULL,
+                stdout=subprocess.PIPE,
+            )
+            ir_file = pp.stdout
 
         if isinstance(cmd_args, list):
             args = [applySubstitutions(a, substitutions) for a in cmd_args]
diff --git a/llvm/utils/git/pre-push.py b/llvm/utils/git/pre-push.py
index d7ae376..dfa009d 100755
--- a/llvm/utils/git/pre-push.py
+++ b/llvm/utils/git/pre-push.py
@@ -27,7 +27,6 @@ From the git doc:
 """
 
 import argparse
-import os
 import shutil
 import subprocess
 import sys
@@ -70,14 +69,6 @@ def ask_confirm(prompt):
         return query.lower() == "y"
 
 
-def get_dev_null():
-    """Lazily create a /dev/null fd for use in shell()"""
-    global dev_null_fd
-    if dev_null_fd is None:
-        dev_null_fd = open(os.devnull, "w")
-    return dev_null_fd
-
-
 def shell(
     cmd,
     strip=True,
@@ -95,10 +86,8 @@ def shell(
         cwd_msg = " in %s" % cwd
     log_verbose("Running%s: %s" % (cwd_msg, " ".join(quoted_cmd)))
 
-    err_pipe = subprocess.PIPE
-    if ignore_errors:
-        # Silence errors if requested.
-        err_pipe = get_dev_null()
+    # Silence errors if requested.
+    err_pipe = subprocess.DEVNULL if ignore_errors else subprocess.PIPE
 
     start = time.time()
     p = subprocess.Popen(
diff --git a/llvm/utils/gn/gn.py b/llvm/utils/gn/gn.py
index 290c694..6b7919b 100755
--- a/llvm/utils/gn/gn.py
+++ b/llvm/utils/gn/gn.py
@@ -42,7 +42,7 @@ def main():
     if (
         subprocess.call(
             "gn --version",
-            stdout=open(os.devnull, "w"),
+            stdout=subprocess.DEVNULL,
             stderr=subprocess.STDOUT,
             shell=True,
         )