Index: docs/CommandGuide/lit.rst
===================================================================
--- docs/CommandGuide/lit.rst
+++ docs/CommandGuide/lit.rst
@@ -358,6 +358,11 @@
  **available_features** A set of features that can be used in `XFAIL`,
  `REQUIRES`, and `UNSUPPORTED` directives.
 
+ **setup_script** A script to run before any of the tests in this suite are
+ executed, or None. May be relative to the directory containing the
+ configuration file. Caution: this script will be run for this directory and
+ *once for every subdirectory.*
+
 TEST DISCOVERY
 ~~~~~~~~~~~~~~
 
@@ -395,17 +400,18 @@
 :program:`lit` provides various patterns that can be used with the RUN command.
 These are defined in TestRunner.py. The base set of substitutions are:
 
- ========== ==============
-  Macro      Substitution
- ========== ==============
- %s         source path (path to the file currently being run)
- %S         source dir (directory of the file currently being run)
- %p         same as %S
- %{pathsep} path separator
- %t         temporary file name unique to the test
- %T         temporary directory unique to the test
- %%         %
- ========== ==============
+ ============== ==============
+  Macro         Substitution
+ ============== ==============
+ %s             source path (path to the file currently being run)
+ %S             source dir (directory of the file currently being run)
+ %p             same as %S
+ %{pathsep}     path separator
+ %t             temporary file name unique to the test
+ %T             temporary directory unique to the test
+ %shared_output temporary directory shared by all tests in the same directory
+ %%             %
+ ============== ==============
 
 Other substitutions are provided that are variations on this base set and
 further substitution patterns can be defined by each test module. See the
Index: docs/TestingGuide.rst
===================================================================
--- docs/TestingGuide.rst
+++ docs/TestingGuide.rst
@@ -292,6 +292,30 @@
   putting the extra files in an ``Inputs/`` directory. This pattern is
   deprecated.
 
+
+Setup scripts
+-------------
+
+Some tests may have common shared setup that would be redundant to perform in
+each test. In this case you can use a local configuration file
+(``lit.local.cfg``) to provide a setup script, using the following bit of
+Python:
+
+.. code-block:: python
+
+  config.setup_script = 'Inputs/base.sh'
+
+The path may be absolute or relative to the configuration file. This script
+will be run before any tests in the directory are executed, with
+``%shared_output`` as its current working directory. The same environment used
+to execute tests in this directory will be used to run the script
+(``config.environment``).
+
+Note that like other configuration, ``setup_script`` is inherited for tests in
+subdirectories. This means the same script may be executed more than once, with
+different working directories.
+
+
 Fragile tests
 -------------
 
@@ -464,6 +488,11 @@
 
    Example: ``/home/user/llvm.build/test/MC/ELF/Output``
 
+``%shared_output``
+   Path to a directory that can be shared across all test cases in the same
+   source directory. The directory may not exist unless you have a setup script,
+   described above.
+
 ``%{pathsep}``
 
    Expands to the path separator, i.e. ``:`` (or ``;`` on Windows).
Index: utils/lit/lit/TestRunner.py
===================================================================
--- utils/lit/lit/TestRunner.py
+++ utils/lit/lit/TestRunner.py
@@ -842,7 +842,9 @@
     substitutions.extend(test.config.substitutions)
     tmpName = tmpBase + '.tmp'
     baseName = os.path.basename(tmpBase)
-    substitutions.extend([('%s', sourcepath),
+    sharedDir = os.path.join(os.path.dirname(tmpName), 'Shared')
+    substitutions.extend([('%shared_output', sharedDir),
+                          ('%s', sourcepath),
                           ('%S', sourcedir),
                           ('%p', sourcedir),
                           ('%{pathsep}', os.pathsep),
@@ -853,6 +855,7 @@
 
     # "%/[STpst]" should be normalized.
     substitutions.extend([
+            ('%/shared_output', sharedDir.replace('\\', '/')),
             ('%/s', sourcepath.replace('\\', '/')),
             ('%/S', sourcedir.replace('\\', '/')),
             ('%/p', sourcedir.replace('\\', '/')),
@@ -863,6 +866,7 @@
     # "%:[STpst]" are paths without colons.
     if kIsWindows:
         substitutions.extend([
+                ('%:shared_output', re.sub(r'^(.):', r'\1', sharedDir)),
                 ('%:s', re.sub(r'^(.):', r'\1', sourcepath)),
                 ('%:S', re.sub(r'^(.):', r'\1', sourcedir)),
                 ('%:p', re.sub(r'^(.):', r'\1', sourcedir)),
@@ -871,6 +875,7 @@
                 ])
     else:
         substitutions.extend([
+                ('%:shared_output', sharedDir),
                 ('%:s', sourcepath),
                 ('%:S', sourcedir),
                 ('%:p', sourcedir),
Index: utils/lit/lit/TestingConfig.py
===================================================================
--- utils/lit/lit/TestingConfig.py
+++ utils/lit/lit/TestingConfig.py
@@ -100,13 +100,13 @@
                 'unable to parse config file %r, traceback: %s' % (
                     path, traceback.format_exc()))
 
-        self.finish(litConfig)
+        self.finish(litConfig, path)
 
     def __init__(self, parent, name, suffixes, test_format,
                  environment, substitutions, unsupported,
                  test_exec_root, test_source_root, excludes,
                  available_features, pipefail, limit_to_features = [],
-                 is_early = False, parallelism_group = ""):
+                 is_early = False, parallelism_group = "", setup_script = None):
         self.parent = parent
         self.name = str(name)
         self.suffixes = set(suffixes)
@@ -126,8 +126,9 @@
         # Whether the suite should be tested early in a given run.
         self.is_early = bool(is_early)
         self.parallelism_group = parallelism_group
+        self.setup_script = setup_script
 
-    def finish(self, litConfig):
+    def finish(self, litConfig, path):
         """finish() - Finish this config object, after loading is complete."""
 
         self.name = str(self.name)
@@ -143,6 +144,9 @@
             # files. Should we distinguish them?
             self.test_source_root = str(self.test_source_root)
         self.excludes = set(self.excludes)
+        if self.setup_script is not None:
+            self.setup_script = os.path.join(os.path.dirname(path),
+                                             self.setup_script)
 
     @property
     def root(self):
Index: utils/lit/lit/run.py
===================================================================
--- utils/lit/lit/run.py
+++ utils/lit/lit/run.py
@@ -36,6 +36,48 @@
         if self.failedCount == self.maxFailures:
             self.provider.cancel()
 
+def _runSetup(test, litConfig):
+    if not test.config.setup_script:
+        raise
+
+    # FIXME: This should be kept in sync with '%shared_output' in the default
+    # substitutions.
+    shared_dir = os.path.join(os.path.dirname(test.getExecPath()),
+                              'Output', 'Shared')
+    lit.util.mkdir_p(shared_dir)
+
+    try:
+        out, err, exitCode = lit.util.executeCommand(
+            [test.config.setup_script],
+            cwd=shared_dir,
+            env=test.config.environment,
+            timeout=litConfig.maxIndividualTestTime)
+        timeoutInfo = None
+    except lit.util.ExecuteCommandTimeoutException as e:
+        out = e.out
+        err = e.err
+        exitCode = e.exitCode
+        timeoutInfo = e.msg
+
+    if exitCode == 0:
+        return
+
+    # Form the output log.
+    output = """Setup Script:\n--\n%s\n--\nExit Code: %d\n""" % (
+        cmd, exitCode)
+
+    if timeoutInfo is not None:
+        output += """Timeout: %s\n""" % (timeoutInfo,)
+    output += "\n"
+
+    # Append the outputs, if present.
+    if out:
+        output += """Command Output (stdout):\n--\n%s\n--\n""" % (out,)
+    if err:
+        output += """Command Output (stderr):\n--\n%s\n--\n""" % (err,)
+
+    raise ValueError(output)
+
 class Run(object):
     """
     This class represents a concrete, configured testing run.
@@ -62,6 +104,23 @@
         if max_time:
             deadline = time.time() + max_time
 
+        # Handle any setup necessary for these tests. Set up outer directories
+        # before inner ones, but promise nothing else.
+        # FIXME: Parallelize this too!
+        seenDirs = set()
+        testsWithSetup = []
+        for test in self.tests:
+            testDir = os.path.dirname(test.getExecPath())
+            if testDir in seenDirs:
+                continue
+            seenDirs.add(testDir)
+            if not test.config.setup_script:
+                continue
+            testsWithSetup.append((test, testDir))
+        testsWithSetup.sort(key=lambda pair: pair[1].count(os.sep))
+        for test, _ in testsWithSetup:
+            _runSetup(test, self.lit_config)
+
         # Start a process pool. Copy over the data shared between all test runs.
         # FIXME: Find a way to capture the worker process stderr. If the user
         # interrupts the workers before we make it into our task callback, they
Index: utils/lit/tests/Inputs/setup-script/Inputs/base.sh
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/Inputs/base.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+
+touch base.txt
+echo $(dirname $(dirname "$PWD")) >> "$SHARED_LOG_FILE"
Index: utils/lit/tests/Inputs/setup-script/lit.cfg
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/lit.cfg
@@ -0,0 +1,10 @@
+import lit.formats
+import os
+
+config.name = 'shtest-shell'
+config.suffixes = ['.txt']
+config.test_format = lit.formats.ShTest()
+config.test_source_root = None
+config.test_exec_root = None
+config.setup_script = 'Inputs/base.sh'
+config.environment['SHARED_LOG_FILE'] = os.environ.get('SHARED_LOG_FILE')
Index: utils/lit/tests/Inputs/setup-script/subdir-custom/Inputs/custom.sh
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/subdir-custom/Inputs/custom.sh
@@ -0,0 +1,4 @@
+#!/bin/bash
+
+touch custom.txt
+$(dirname "$0")/../../Inputs/base.sh
Index: utils/lit/tests/Inputs/setup-script/subdir-custom/lit.local.cfg
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/subdir-custom/lit.local.cfg
@@ -0,0 +1 @@
+config.setup_script = 'Inputs/custom.sh'
Index: utils/lit/tests/Inputs/setup-script/subdir-custom/test.txt
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/subdir-custom/test.txt
@@ -0,0 +1,2 @@
+RUN: test -f %shared_output/base.txt
+RUN: test -f %shared_output/custom.txt
Index: utils/lit/tests/Inputs/setup-script/subdir-inherited/lit.local.cfg
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/subdir-inherited/lit.local.cfg
@@ -0,0 +1 @@
+# No extra configuration, but we should still get the setup script run.
Index: utils/lit/tests/Inputs/setup-script/subdir-inherited/test.txt
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/subdir-inherited/test.txt
@@ -0,0 +1 @@
+RUN: test -f %shared_output/base.txt
Index: utils/lit/tests/Inputs/setup-script/subdir-no-local/test.txt
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/subdir-no-local/test.txt
@@ -0,0 +1 @@
+RUN: test -f %shared_output/base.txt
Index: utils/lit/tests/Inputs/setup-script/subdir-no-setup/lit.local.cfg
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/subdir-no-setup/lit.local.cfg
@@ -0,0 +1 @@
+config.setup_script = None
Index: utils/lit/tests/Inputs/setup-script/subdir-no-setup/test.txt
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/subdir-no-setup/test.txt
@@ -0,0 +1 @@
+RUN: not test -d %shared_output
\ No newline at end of file
Index: utils/lit/tests/Inputs/setup-script/test.txt
===================================================================
--- /dev/null
+++ utils/lit/tests/Inputs/setup-script/test.txt
@@ -0,0 +1 @@
+RUN: test -f %shared_output/base.txt
\ No newline at end of file
Index: utils/lit/tests/setup-script.py
===================================================================
--- /dev/null
+++ utils/lit/tests/setup-script.py
@@ -0,0 +1,31 @@
+# Test the 'setup_script' feature.
+
+# RUN: rm -rf %t %t.log.txt
+# RUN: cp -r %{inputs}/setup-script %t
+# RUN: env SHARED_LOG_FILE=%t.log.txt %{lit} -j 1 -v %t
+# RUN: FileCheck %s < %t.log.txt
+# RUN: FileCheck -check-prefix=NEGATIVE %s < %t.log.txt
+
+# RUN: rm -rf %t-shuffle %t-shuffle.log.txt
+# RUN: cp -r %{inputs}/setup-script %t-shuffle
+# RUN: env SHARED_LOG_FILE=%t-shuffle.log.txt %{lit} -j 1 -v --shuffle %t-shuffle
+# RUN: FileCheck %s < %t-shuffle.log.txt
+# RUN: FileCheck -check-prefix=NEGATIVE %s < %t-shuffle.log.txt
+
+# RUN: rm -rf %t-specific %t-specific.log.txt
+# RUN: cp -r %{inputs}/setup-script %t-specific
+# RUN: env SHARED_LOG_FILE=%t-specific.log.txt %{lit} -j 1 -v %t-specific/subdir-inherited
+# RUN: FileCheck -check-prefix=CHECK-SPECIFIC %s < %t-specific.log.txt
+# RUN: FileCheck -check-prefix=CHECK-SPECIFIC-NEGATIVE %s < %t-specific.log.txt
+
+# CHECK: setup-script.py.tmp{{(-shuffle)?}}{{$}}
+# CHECK-DAG: setup-script.py.tmp{{(-shuffle)?}}/subdir-custom{{$}}
+# CHECK-DAG: setup-script.py.tmp{{(-shuffle)?}}/subdir-inherited{{$}}
+# CHECK-DAG: setup-script.py.tmp{{(-shuffle)?}}/subdir-no-local{{$}}
+# NEGATIVE-NOT: subdir-no-setup
+
+# CHECK-SPECIFIC: setup-script.py.tmp-specific/subdir-inherited{{$}}
+# CHECK-SPECIFIC-NEGATIVE-NOT: setup-script.py.tmp-specific{{$}}
+# CHECK-SPECIFIC-NEGATIVE-NOT: subdir-custom
+# CHECK-SPECIFIC-NEGATIVE-NOT: subdir-no-local
+# CHECK-SPECIFIC-NEGATIVE-NOT: subdir-no-setup