Index: llvm/trunk/utils/bugpoint_gisel_reducer.py
===================================================================
--- llvm/trunk/utils/bugpoint_gisel_reducer.py
+++ llvm/trunk/utils/bugpoint_gisel_reducer.py
@@ -0,0 +1,146 @@
+#!/usr/bin/env python
+
+"""Reduces GlobalISel failures.
+
+This script is a utility to reduce tests that GlobalISel
+fails to compile.
+
+It runs llc to get the error message using a regex and creates
+a custom command to check that specific error. Then, it runs bugpoint
+with the custom command.
+
+"""
+from __future__ import print_function
+import argparse
+import re
+import subprocess
+import sys
+import tempfile
+import os
+
+
+def log(msg):
+    print(msg)
+
+
+def hr():
+    log('-' * 50)
+
+
+def log_err(msg):
+    print('ERROR: {}'.format(msg), file=sys.stderr)
+
+
+def check_path(path):
+    if not os.path.exists(path):
+        log_err('{} does not exist.'.format(path))
+        raise
+    return path
+
+
+def check_bin(build_dir, bin_name):
+    file_name = '{}/bin/{}'.format(build_dir, bin_name)
+    return check_path(file_name)
+
+
+def run_llc(llc, irfile):
+    pr = subprocess.Popen([llc,
+                           '-o',
+                           '-',
+                           '-global-isel',
+                           '-pass-remarks-missed=gisel',
+                           irfile],
+                          stdout=subprocess.PIPE,
+                          stderr=subprocess.PIPE)
+    out, err = pr.communicate()
+    res = pr.wait()
+    if res == 0:
+        return 0
+    re_err = re.compile(
+        r'LLVM ERROR: ([a-z\s]+):.*(G_INTRINSIC[_A-Z]* <intrinsic:@[a-zA-Z0-9\.]+>|G_[A-Z_]+)')
+    match = re_err.match(err)
+    if not match:
+        return 0
+    else:
+        return [match.group(1), match.group(2)]
+
+
+def run_bugpoint(bugpoint_bin, llc_bin, opt_bin, tmp, ir_file):
+    compileCmd = '-compile-command={} -c {} {}'.format(
+        os.path.realpath(__file__), llc_bin, tmp)
+    pr = subprocess.Popen([bugpoint_bin,
+                           '-compile-custom',
+                           compileCmd,
+                           '-opt-command={}'.format(opt_bin),
+                           ir_file])
+    res = pr.wait()
+    if res != 0:
+        log_err("Unable to reduce the test.")
+        raise
+
+
+def run_bugpoint_check():
+    path_to_llc = sys.argv[2]
+    path_to_err = sys.argv[3]
+    path_to_ir = sys.argv[4]
+    with open(path_to_err, 'r') as f:
+        err = f.read()
+        res = run_llc(path_to_llc, path_to_ir)
+        if res == 0:
+            return 0
+        log('GlobalISed failed, {}: {}'.format(res[0], res[1]))
+        if res != err.split(';'):
+            return 0
+        else:
+            return 1
+
+
+def main():
+    # Check if this is called by bugpoint.
+    if len(sys.argv) == 5 and sys.argv[1] == '-c':
+        sys.exit(run_bugpoint_check())
+
+    # Parse arguments.
+    parser = argparse.ArgumentParser(
+        description=__doc__, formatter_class=argparse.RawTextHelpFormatter)
+    parser.add_argument('BuildDir', help="Path to LLVM build directory")
+    parser.add_argument('IRFile', help="Path to the input IR file")
+    args = parser.parse_args()
+
+    # Check if the binaries exist.
+    build_dir = check_path(args.BuildDir)
+    ir_file = check_path(args.IRFile)
+    llc_bin = check_bin(build_dir, 'llc')
+    opt_bin = check_bin(build_dir, 'opt')
+    bugpoint_bin = check_bin(build_dir, 'bugpoint')
+
+    # Run llc to see if GlobalISel fails.
+    log('Running llc...')
+    res = run_llc(llc_bin, ir_file)
+    if res == 0:
+        log_err("Expected failure")
+        raise
+    hr()
+    log('GlobalISel failed, {}: {}.'.format(res[0], res[1]))
+    tmp = tempfile.NamedTemporaryFile()
+    log('Writing error to {} for bugpoint.'.format(tmp.name))
+    tmp.write(';'.join(res))
+    tmp.flush()
+    hr()
+
+    # Run bugpoint.
+    log('Running bugpoint...')
+    run_bugpoint(bugpoint_bin, llc_bin, opt_bin, tmp.name, ir_file)
+    hr()
+    log('Done!')
+    hr()
+    output_file = 'bugpoint-reduced-simplified.bc'
+    log('Run llvm-dis to disassemble the output:')
+    log('$ {}/bin/llvm-dis -o - {}'.format(build_dir, output_file))
+    log('Run llc to reproduce the problem:')
+    log('$ {}/bin/llc -o - -global-isel '
+        '-pass-remarks-missed=gisel {}'.format(build_dir, output_file))
+
+
+if __name__ == '__main__':
+    main()