[NPM] Automatic 'opt' pipeline reducer script.

[markus]

Summary

Script for automatic 'opt' pipeline reduction for when using the new
pass-manager (NPM). Based around the '-print-pipeline-passes' option.

The reduction algorithm consists of several phases (steps).

Step #0: Verify that input fails with the given pipeline and make note of the
error code.

Step #1: Split pipeline in two starting from front and move forward as long as
first pipeline exits normally and the second pipeline fails with the expected
error code. Move on to step #2 with the IR from the split point and the
pipeline from the second invocation.

Step #2: Remove passes from end of the pipeline as long as the pipeline fails
with the expected error code.

Step #3: Make several sweeps over the remaining pipeline trying to remove one
pass at a time. Repeat sweeps until unable to remove any more passes.

Usage example:
./utils/reduce_pipeline.py --opt-binary=./build-all-Debug/bin/opt --input=input.ll --output=output.ll --passes=PIPELINE [EXTRA-OPT-ARGS ...]

[markus]

For testing the following can be tried. First re-introduce a bug in opt by reverting the following revert

commit 1fbdbb559569641f6d509b569966901c8fb02b63
Author: Florian Hahn <[e-mail]>
Date:   Thu Sep 30 18:52:38 2021 +0100

    Revert "Recommit "[SCEV] Look through single value PHIs." (take 2)"

    This reverts commit 764d9aa97905f202385b4f25f8d234630b4feef3.

    This patch exposed a few additional cases where SCEV expressions are not
    properly invalidated.

    See PR52024, PR52023.

then running

./utils/reduce_pipeline.py --opt-binary=../build-debug/bin/opt --input=bbi-60925.ll --output=test2.ll --passes='canonicalize-aliases,objc-arc-apelim,cgscc(require<no-op-cgscc>,argpromotion,invalidate<all>,no-op-cgscc),objc-arc-apelim,function(function(aa-eval,loop-mssa(lnicm,licm,loop-instsimplify,indvars,loop-idiom),loop(indvars,require<iv-users>,loop-unroll-and-jam,simple-loop-unswitch<nontrivial>,loop-unroll-full),invalidate<all>)),function(early-cse<memssa>,loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only>,early-cse<memssa>,verify<memoryssa>,loop-mssa(require<pass-instrumentation>,loop-deletion),alignment-from-assumptions)'

bbi-60925.ll1 KBDownload

should result in

The following extra args will be passed to opt: []
---Starting step #0---
-passes="canonicalize-aliases,objc-arc-apelim,cgscc(require<no-op-cgscc>,argpromotion,invalidate<all>,no-op-cgscc),objc-arc-apelim,function(function(aa-eval,loop-mssa(lnicm,licm,loop-instsimplify,indvars,loop-idiom),loop(indvars,require<iv-users>,loop-unroll-and-jam,simple-loop-unswitch<nontrivial>,loop-unroll-full),invalidate<all>)),function(early-cse<memssa>,loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only>,early-cse<memssa>,verify<memoryssa>,loop-mssa(require<pass-instrumentation>,loop-deletion),alignment-from-assumptions)"
---Starting step #1---
-passes="function(function(loop-mssa(lnicm,licm,loop-instsimplify,indvars,loop-idiom),loop(indvars,require<iv-users>,loop-unroll-and-jam,simple-loop-unswitch<nontrivial>,loop-unroll-full),invalidate<all>)),function(early-cse<memssa>,loop-vectorize<no-interleave-forced-only;no-vectorize-forced-only>,early-cse<memssa>,verify<memoryssa>,loop-mssa(require<pass-instrumentation>,loop-deletion),alignment-from-assumptions)"
---Starting step #2---
-passes="function(function(loop-mssa(lnicm,licm,loop-instsimplify,indvars,loop-idiom),loop(indvars,require<iv-users>,loop-unroll-and-jam,simple-loop-unswitch<nontrivial>,loop-unroll-full)))"
---Starting step #3---
-passes="function(function(loop-mssa(licm,loop-instsimplify,indvars),loop(indvars,simple-loop-unswitch<nontrivial>,loop-unroll-full)))"
---FINISHED---
Wrote output to 'test2.ll'.
-passes="function(function(loop-mssa(licm,loop-instsimplify,indvars),loop(indvars,simple-loop-unswitch<nontrivial>,loop-unroll-full)))"

[markus]

Added some docstrings.

[aeubanks]

We could have a test by passing a fake --opt-binary that checks the -passes it receives and returns 0 or 1 by checking that some arbitrary set of passes is in the -passes pipeline

[markus]

I thought about that too but where do we put tests for scripts in llvm/utils?

[aeubanks]

I've done https://reviews.llvm.org/D107184 before, basically put tests in their own directory.

[markus]

Ok, cool. I guess it is sufficient to have the tests separated like that since they only need to be run when changes are made to the script.

[markus]

Something like this and then perhaps add a few more tests and documenting them a bit?

[fhahn]

Great to see progress on this! For a bit of extra convenience, it might be helpful to accept -passes=defaults<O3> & co and automatically translate that to the explicit pass invocation.

[markus]

In D110908#3039639, @fhahn wrote:

Great to see progress on this! For a bit of extra convenience, it might be helpful to accept -passes=defaults<O3> & co and automatically translate that to the explicit pass invocation.

One can always do e.g. ./utils/reduce_pipeline.py --opt-binary=../build-debug/bin/opt --input=bbi-60925.ll --output=test2.ll --passes=$(../build-debug/bin/opt -passes='default<O3>' -print-pipeline-passes -disable-output bbi-60925.ll) but I agree that is a bit inconvenient and requires a bit of redundant typing.
Maybe it is worth it to have the script automatically invoke opt one time at the start to expand the pipeline with -print-pipeline-passes, if the pipeline is already expanded it should simply be an identity operation.

[aeubanks]

In D110908#3039668, @markus wrote:

In D110908#3039639, @fhahn wrote:

Great to see progress on this! For a bit of extra convenience, it might be helpful to accept -passes=defaults<O3> & co and automatically translate that to the explicit pass invocation.

One can always do e.g. ./utils/reduce_pipeline.py --opt-binary=../build-debug/bin/opt --input=bbi-60925.ll --output=test2.ll --passes=$(../build-debug/bin/opt -passes='default<O3>' -print-pipeline-passes -disable-output bbi-60925.ll) but I agree that is a bit inconvenient and requires a bit of redundant typing.
Maybe it is worth it to have the script automatically invoke opt one time at the start to expand the pipeline with -print-pipeline-passes, if the pipeline is already expanded it should simply be an identity operation.

+1

[markus]

Added option for automatic expansion of default pipelines. E.g. now one can do

./utils/reduce_pipeline.py --opt-binary=../build-debug/bin/opt --input=bbi-60925.ll --output=test2.ll --passes='default<O3>' --expand-passes

and that will expand the pipeline (using a separate opt invocation with -print-pipeline-passes) before starting the reduction. In this particular case there will be no reduction as the crash does not reproduce with the default pipeline but that is a different matter. One test has been added for the expansion using fake_opt.py.

[aeubanks]

looks good, thanks!

llvm/utils/reduce_pipeline.py

46

I think automatically doing this would be a bit simpler, but not a huge deal

113

very unlikely that this will matter, but perhaps pruning empty pass managers might cause crashes to go away, checking before pruning would be nice

[markus]

Thanks for reviewing!

llvm/utils/reduce_pipeline.py

46

I'll negate the option so it is on by default but possible to disable if it breaks for some reason.

113

Agree that seems unlikely but I'll add a second option for disabling the pruning just in case.

llvm/utils/pipeline.py

+# Automatically formatted with yapf (https://github.com/google/yapf)
+"""Utility functions for creating and manipulating LLVM 'opt' NPM pipeline objects."""
+
+
+def fromStr(pipeStr):
+    """Create pipeline object from string representation."""
+    stack = []
+    curr = []
+    tok = ''
+    kind = ''
+    for c in pipeStr:
+        if c == ',':
+            if tok != '':
+                curr.append([None, tok])
+            tok = ''
+        elif c == '(':
+            stack.append([kind, curr])
+            kind = tok
+            curr = []
+            tok = ''
+        elif c == ')':
+            if tok != '':
+                curr.append([None, tok])
+            tok = ''
+            oldKind = kind
+            oldCurr = curr
+            [kind, curr] = stack.pop()
+            curr.append([oldKind, oldCurr])
+        else:
+            tok += c
+    if tok != '':
+        curr.append([None, tok])
+    return curr
+
+
+def toStr(pipeObj):
+    """Create string representation of pipeline object."""
+    res = ''
+    lastIdx = len(pipeObj) - 1
+    for i, c in enumerate(pipeObj):
+        if c[0]:
+            res += c[0] + '('
+            res += toStr(c[1])
+            res += ')'
+        else:
+            res += c[1]
+        if i != lastIdx:
+            res += ','
+    return res
+
+
+def count(pipeObj):
+    """Count number of passes (pass-managers excluded) in pipeline object."""
+    cnt = 0
+    for c in pipeObj:
+        if c[0]:
+            cnt += count(c[1])
+        else:
+            cnt += 1
+    return cnt
+
+
+def split(pipeObj, splitIndex):
+    """Create two new pipeline objects by splitting pipeObj in two directly after pass with index splitIndex."""
+    def splitInt(src, splitIndex, dstA, dstB, idx):
+        for s in src:
+            if s[0]:
+                dstA2 = []
+                dstB2 = []
+                idx = splitInt(s[1], splitIndex, dstA2, dstB2, idx)
+                dstA.append([s[0], dstA2])
+                dstB.append([s[0], dstB2])
+            else:
+                if idx <= splitIndex:
+                    dstA.append([None, s[1]])
+                else:
+                    dstB.append([None, s[1]])
+                idx += 1
+        return idx
+
+    listA = []
+    listB = []
+    splitInt(pipeObj, splitIndex, listA, listB, 0)
+    return [listA, listB]
+
+
+def remove(pipeObj, removeIndex):
+    """Create new pipeline object by removing pass with index removeIndex from pipeObj."""
+    def removeInt(src, removeIndex, dst, idx):
+        for s in src:
+            if s[0]:
+                dst2 = []
+                idx = removeInt(s[1], removeIndex, dst2, idx)
+                dst.append([s[0], dst2])
+            else:
+                if idx != removeIndex:
+                    dst.append([None, s[1]])
+                idx += 1
+        return idx
+
+    dst = []
+    removeInt(pipeObj, removeIndex, dst, 0)
+    return dst
+
+
+def copy(srcPipeObj):
+    """Create copy of pipeline object srcPipeObj."""
+    def copyInt(dst, src):
+        for s in src:
+            if s[0]:
+                dst2 = []
+                copyInt(dst2, s[1])
+                dst.append([s[0], dst2])
+            else:
+                dst.append([None, s[1]])
+
+    dstPipeObj = []
+    copyInt(dstPipeObj, srcPipeObj)
+    return dstPipeObj
+
+
+def prune(srcPipeObj):
+    """Create new pipeline object by removing empty pass-managers (those with count = 0) from srcPipeObj."""
+    def pruneInt(dst, src):
+        for s in src:
+            if s[0]:
+                if count(s[1]):
+                    dst2 = []
+                    pruneInt(dst2, s[1])
+                    dst.append([s[0], dst2])
+            else:
+                dst.append([None, s[1]])
+
+    dstPipeObj = []
+    pruneInt(dstPipeObj, srcPipeObj)
+    return dstPipeObj
+
+
+if __name__ == "__main__":
+    import unittest
+
+    class Test(unittest.TestCase):
+        def test_0(self):
+            pipeStr = 'a,b,A(c,B(d,e),f),g'
+            pipeObj = fromStr(pipeStr)
+
+            self.assertEqual(7, count(pipeObj))
+
+            self.assertEqual(pipeObj, pipeObj)
+            self.assertEqual(pipeObj, prune(pipeObj))
+            self.assertEqual(pipeObj, copy(pipeObj))
+
+            self.assertEqual(pipeStr, toStr(pipeObj))
+            self.assertEqual(pipeStr, toStr(prune(pipeObj)))
+            self.assertEqual(pipeStr, toStr(copy(pipeObj)))
+
+            [pipeObjA, pipeObjB] = split(pipeObj, 3)
+            self.assertEqual('a,b,A(c,B(d))', toStr(pipeObjA))
+            self.assertEqual('A(B(e),f),g', toStr(pipeObjB))
+
+            self.assertEqual('b,A(c,B(d,e),f),g', toStr(remove(pipeObj, 0)))
+            self.assertEqual('a,b,A(c,B(d,e),f)', toStr(remove(pipeObj, 6)))
+
+            pipeObjC = remove(pipeObj, 4)
+            self.assertEqual('a,b,A(c,B(d),f),g', toStr(pipeObjC))
+            pipeObjC = remove(pipeObjC, 3)
+            self.assertEqual('a,b,A(c,B(),f),g', toStr(pipeObjC))
+            pipeObjC = prune(pipeObjC)
+            self.assertEqual('a,b,A(c,f),g', toStr(pipeObjC))
+
+    unittest.main()
+    exit(0)

llvm/utils/reduce_pipeline.py

+#!/usr/bin/env python3
+
+# Automatically formatted with yapf (https://github.com/google/yapf)
+
+# Script for automatic 'opt' pipeline reduction for when using the new
+# pass-manager (NPM). Based around the '-print-pipeline-passes' option.
+#
+# The reduction algorithm consists of several phases (steps).
+#
+# Step #0: Verify that input fails with the given pipeline and make note of the
+# error code.
+#
+# Step #1: Split pipeline in two starting from front and move forward as long as
+# first pipeline exits normally and the second pipeline fails with the expected
+# error code. Move on to step #2 with the IR from the split point and the
+# pipeline from the second invocation.
+#
+# Step #2: Remove passes from end of the pipeline as long as the pipeline fails
+# with the expected error code.
+#
+# Step #3: Make several sweeps over the remaining pipeline trying to remove one
+# pass at a time. Repeat sweeps until unable to remove any more passes.
+#
+# Usage example:
+# reduce_pipeline.py --opt-binary=./build-all-Debug/bin/opt --input=input.ll --output=output.ll --passes=PIPELINE [EXTRA-OPT-ARGS ...]
+
+import argparse
+import pipeline
+import shutil
+import subprocess
+import tempfile
+
+parser = argparse.ArgumentParser(
+    description=
+    'Automatic opt pipeline reducer. Unrecognized arguments are forwarded to opt.'
+)
+parser.add_argument('--opt-binary',
+                    action='store',
+                    dest='opt_binary',
+                    default='opt')
+parser.add_argument('--passes', action='store', dest='passes', required=True)
+parser.add_argument('--input', action='store', dest='input', required=True)
+parser.add_argument('--output', action='store', dest='output')
+parser.add_argument('--dont-expand-passes',
+                    action='store_true',
+                    dest='dont_expand_passes',
+                    help='Do not expand pipeline before starting reduction.')
+parser.add_argument(
+    '--dont-remove-empty-pm',
+    action='store_true',
+    dest='dont_remove_empty_pm',
+    help='Do not remove empty pass-managers from the pipeline during reduction.'
+)
+[args, extra_opt_args] = parser.parse_known_args()
+
+print('The following extra args will be passed to opt: {}'.format(
+    extra_opt_args))
+
+lst = pipeline.fromStr(args.passes)
+passes = '-passes={}'.format(pipeline.toStr(lst))
+ll_input = args.input
+
+# Step #-1
+# Launch 'opt' once with '-print-pipeline-passes' to expand pipeline before
+# starting reduction. Allows specifying a default pipelines (e.g.
+# '-passes=default<O3>').
+if not args.dont_expand_passes:
+    run_args = [
+        args.opt_binary, '-disable-symbolication', '-disable-output',
+        '-print-pipeline-passes', passes, ll_input
+    ]
+    run_args.extend(extra_opt_args)
+    opt = subprocess.run(run_args,
+                         stdout=subprocess.PIPE,
+                         stderr=subprocess.PIPE)
+    if opt.returncode != 0:
+        print('Failed to expand passes. Aborting.')
+        print(run_args)
+        print('exitcode: {}'.format(opt.returncode))
+        print(opt.stderr.decode())
+        exit(1)
+    stdout = opt.stdout.decode()
+    stdout = stdout[:stdout.rfind('\n')]
+    print('Expanded pass sequence: {}'.format(stdout))
+    passes = '-passes={}'.format(stdout)
+
+# Step #0
+# Confirm that the given input, passes and options result in failure.
+print('---Starting step #0---')
+run_args = [
+    args.opt_binary, '-disable-symbolication', '-disable-output', passes,
+    ll_input
+]
+run_args.extend(extra_opt_args)
+opt = subprocess.run(run_args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+if opt.returncode >= 0:
+    print('Input does not result in failure as expected. Aborting.')
+    print(run_args)
+    print('exitcode: {}'.format(opt.returncode))
+    print(opt.stderr.decode())
+    exit(1)
+
+expected_error_returncode = opt.returncode
+print('-passes="{}"'.format(pipeline.toStr(lst)))
+
+# Step #1
+# Try to narrow down the failing pass sequence by splitting the pipeline in two
+# opt invocations (A and B) starting with invocation A only running the first
+# pipeline pass and invocation B the remaining. Keep moving the split point
+# forward as long as invocation A exits normally and invocation B fails with
+# the expected error. This will accomplish two things first the input IR will be
+# further reduced and second, with that IR, the reduced pipeline for invocation
+# B will be sufficient to reproduce.
+print('---Starting step #1---')
+prevLstB = None
+prevIntermediate = None
+tmpd = tempfile.TemporaryDirectory()
+
+for idx in range(pipeline.count(lst)):
+    [lstA, lstB] = pipeline.split(lst, idx)
+    if not args.dont_remove_empty_pm:
+        lstA = pipeline.prune(lstA)
+        lstB = pipeline.prune(lstB)
+    passesA = '-passes=' + pipeline.toStr(lstA)
+    passesB = '-passes=' + pipeline.toStr(lstB)
+
+    intermediate = 'intermediate-0.ll' if idx % 2 else 'intermediate-1.ll'
+    intermediate = tmpd.name + '/' + intermediate
+    run_args = [
+        args.opt_binary, '-disable-symbolication', '-S', '-o', intermediate,
+        passesA, ll_input
+    ]
+    run_args.extend(extra_opt_args)
+    optA = subprocess.run(run_args,
+                          stdout=subprocess.PIPE,
+                          stderr=subprocess.PIPE)
+    run_args = [
+        args.opt_binary, '-disable-symbolication', '-disable-output', passesB,
+        intermediate
+    ]
+    run_args.extend(extra_opt_args)
+    optB = subprocess.run(run_args,
+                          stdout=subprocess.PIPE,
+                          stderr=subprocess.PIPE)
+    if not (optA.returncode == 0
+            and optB.returncode == expected_error_returncode):
+        break
+    prevLstB = lstB
+    prevIntermediate = intermediate
+if prevLstB:
+    lst = prevLstB
+    ll_input = prevIntermediate
+print('-passes="{}"'.format(pipeline.toStr(lst)))
+
+# Step #2
+# Try removing passes from the end of the remaining pipeline while still
+# reproducing the error.
+print('---Starting step #2---')
+prevLstA = None
+for idx in reversed(range(pipeline.count(lst))):
+    [lstA, lstB] = pipeline.split(lst, idx)
+    if not args.dont_remove_empty_pm:
+        lstA = pipeline.prune(lstA)
+    passesA = '-passes=' + pipeline.toStr(lstA)
+    run_args = [
+        args.opt_binary, '-disable-symbolication', '-disable-output', passesA,
+        ll_input
+    ]
+    run_args.extend(extra_opt_args)
+    optA = subprocess.run(run_args,
+                          stdout=subprocess.PIPE,
+                          stderr=subprocess.PIPE)
+    if optA.returncode != expected_error_returncode:
+        break
+    prevLstA = lstA
+if prevLstA:
+    lst = prevLstA
+print('-passes="{}"'.format(pipeline.toStr(lst)))
+
+# Step #3
+# Now that we have a pipeline that is reduced both front and back we do
+# exhaustive sweeps over the remainder trying to remove one pass at a time.
+# Repeat as long as reduction is possible.
+print('---Starting step #3---')
+while True:
+    keepGoing = False
+    for idx in range(pipeline.count(lst)):
+        candLst = pipeline.remove(lst, idx)
+        if not args.dont_remove_empty_pm:
+            candLst = pipeline.prune(candLst)
+        passes = '-passes=' + pipeline.toStr(candLst)
+        run_args = [
+            args.opt_binary, '-disable-symbolication', '-disable-output',
+            passes, ll_input
+        ]
+        run_args.extend(extra_opt_args)
+        opt = subprocess.run(run_args,
+                             stdout=subprocess.PIPE,
+                             stderr=subprocess.PIPE)
+        if opt.returncode == expected_error_returncode:
+            lst = candLst
+            keepGoing = True
+    if not keepGoing:
+        break
+print('-passes="{}"'.format(pipeline.toStr(lst)))
+
+print('---FINISHED---')
+if args.output:
+    shutil.copy(ll_input, args.output)
+    print('Wrote output to \'{}\'.'.format(args.output))
+print('-passes="{}"'.format(pipeline.toStr(lst)))
+exit(0)

llvm/utils/reduce_pipeline_test/fake_opt.py

+#!/usr/bin/env python3
+
+# Automatically formatted with yapf (https://github.com/google/yapf)
+
+# Fake 'opt' program that can be made to crash on request. For testing
+# the 'reduce_pipeline.py' automatic 'opt' NPM pipeline reducer.
+
+import argparse
+import os
+import shutil
+import signal
+
+parser = argparse.ArgumentParser()
+parser.add_argument('-passes', action='store', dest='passes', required=True)
+parser.add_argument('-print-pipeline-passes',
+                    dest='print_pipeline_passes',
+                    action='store_true')
+parser.add_argument('-crash-seq',
+                    action='store',
+                    dest='crash_seq',
+                    required=True)
+parser.add_argument('-o', action='store', dest='output')
+parser.add_argument('input')
+[args, unknown_args] = parser.parse_known_args()
+
+# Echo pipeline if '-print-pipeline-passes'.
+if args.print_pipeline_passes:
+    print(args.passes)
+    exit(0)
+
+# Parse '-crash-seq'.
+crash_seq = []
+tok = ''
+for c in args.crash_seq:
+    if c == ',':
+        if tok != '':
+            crash_seq.append(tok)
+        tok = ''
+    else:
+        tok += c
+if tok != '':
+    crash_seq.append(tok)
+print(crash_seq)
+
+# Parse '-passes' and see if we need to crash.
+tok = ''
+for c in args.passes:
+    if c == ',':
+        if len(crash_seq) > 0 and crash_seq[0] == tok:
+            crash_seq.pop(0)
+        tok = ''
+    elif c == '(':
+        tok = ''
+    elif c == ')':
+        if len(crash_seq) > 0 and crash_seq[0] == tok:
+            crash_seq.pop(0)
+        tok = ''
+    else:
+        tok += c
+if len(crash_seq) > 0 and crash_seq[0] == tok:
+    crash_seq.pop(0)
+
+# Copy input to output.
+if args.output:
+    shutil.copy(args.input, args.output)
+
+# Crash if all 'crash_seq' passes occured in right order.
+if len(crash_seq) == 0:
+    print('crash')
+    os.kill(os.getpid(), signal.SIGKILL)
+else:
+    print('no crash')
+    exit(0)

llvm/utils/reduce_pipeline_test/test.py

+#!/usr/bin/env python3
+
+# Automatically formatted with yapf (https://github.com/google/yapf)
+
+import subprocess
+import unittest
+
+
+def getFinalPasses(run):
+    stdout = run.stdout.decode()
+    stdout = stdout[:stdout.rfind('\n')]
+    stdout = stdout[stdout.rfind('\n') + 1:]
+    return stdout
+
+
+class Test(unittest.TestCase):
+    def test_0(self):
+        """Test all passes are removed except those required to crash. Verify
+           that PM structure is intact."""
+        run_args = [
+            './utils/reduce_pipeline.py',
+            '--opt-binary=./utils/reduce_pipeline_test/fake_opt.py',
+            '--input=/dev/null', '--passes=a,b,c,A(d,B(e,f),g),h,i',
+            '-crash-seq=b,d,f'
+        ]
+        run = subprocess.run(run_args,
+                             stdout=subprocess.PIPE,
+                             stderr=subprocess.PIPE)
+        self.assertEqual(run.returncode, 0)
+        self.assertEqual(getFinalPasses(run), '-passes="b,A(d,B(f))"')
+
+    def test_1(self):
+        """Test all passes are removed except those required to crash. The
+           required passes in this case are the first and last in that order
+           (a bit of a corner-case for the reduction algorithm)."""
+        run_args = [
+            './utils/reduce_pipeline.py',
+            '--opt-binary=./utils/reduce_pipeline_test/fake_opt.py',
+            '--input=/dev/null', '--passes=a,b,c,A(d,B(e,f),g),h,i',
+            '-crash-seq=a,i'
+        ]
+        run = subprocess.run(run_args,
+                             stdout=subprocess.PIPE,
+                             stderr=subprocess.PIPE)
+        self.assertEqual(run.returncode, 0)
+        self.assertEqual(getFinalPasses(run), '-passes="a,i"')
+
+    def test_2(self):
+        """Test the '--dont-expand-passes' option."""
+        run_args = [
+            './utils/reduce_pipeline.py',
+            '--opt-binary=./utils/reduce_pipeline_test/fake_opt.py',
+            '--input=/dev/null', '--passes=a,b,c,A(d,B(e,f),g),h,i',
+            '-crash-seq=b,d,f', '--dont-expand-passes'
+        ]
+        run = subprocess.run(run_args,
+                             stdout=subprocess.PIPE,
+                             stderr=subprocess.PIPE)
+        self.assertEqual(run.returncode, 0)
+        self.assertEqual(getFinalPasses(run), '-passes="b,A(d,B(f))"')
+
+    def test_3(self):
+        """Test that empty pass-managers get removed by default."""
+        run_args = [
+            './utils/reduce_pipeline.py',
+            '--opt-binary=./utils/reduce_pipeline_test/fake_opt.py',
+            '--input=/dev/null', '--passes=a,b,c,A(d,B(e,f),g),h,i',
+            '-crash-seq=b,d,h'
+        ]
+        run = subprocess.run(run_args,
+                             stdout=subprocess.PIPE,
+                             stderr=subprocess.PIPE)
+        self.assertEqual(run.returncode, 0)
+        self.assertEqual(getFinalPasses(run), '-passes="b,A(d),h"')
+
+    def test_4(self):
+        """Test the '--dont-remove-empty-pm' option."""
+        run_args = [
+            './utils/reduce_pipeline.py',
+            '--opt-binary=./utils/reduce_pipeline_test/fake_opt.py',
+            '--input=/dev/null', '--passes=a,b,c,A(d,B(e,f),g),h,i',
+            '-crash-seq=b,d,h', '--dont-remove-empty-pm'
+        ]
+        run = subprocess.run(run_args,
+                             stdout=subprocess.PIPE,
+                             stderr=subprocess.PIPE)
+        self.assertEqual(run.returncode, 0)
+        self.assertEqual(getFinalPasses(run), '-passes="b,A(d,B()),h"')
+
+
+unittest.main()
+exit(0)