--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/utils/shuffle_fuzz.py	Mon May 25 11:07:02 2020 +0900
@@ -0,0 +1,257 @@
+#!/usr/bin/env python
+
+"""A shuffle vector fuzz tester.
+
+This is a python program to fuzz test the LLVM shufflevector instruction. It
+generates a function with a random sequnece of shufflevectors, maintaining the
+element mapping accumulated across the function. It then generates a main
+function which calls it with a different value in each element and checks that
+the result matches the expected mapping.
+
+Take the output IR printed to stdout, compile it to an executable using whatever
+set of transforms you want to test, and run the program. If it crashes, it found
+a bug.
+"""
+
+from __future__ import print_function
+
+import argparse
+import itertools
+import random
+import sys
+import uuid
+
+def main():
+  element_types=['i8', 'i16', 'i32', 'i64', 'f32', 'f64']
+  parser = argparse.ArgumentParser(description=__doc__)
+  parser.add_argument('-v', '--verbose', action='store_true',
+                      help='Show verbose output')
+  parser.add_argument('--seed', default=str(uuid.uuid4()),
+                      help='A string used to seed the RNG')
+  parser.add_argument('--max-shuffle-height', type=int, default=16,
+                      help='Specify a fixed height of shuffle tree to test')
+  parser.add_argument('--no-blends', dest='blends', action='store_false',
+                      help='Include blends of two input vectors')
+  parser.add_argument('--fixed-bit-width', type=int, choices=[128, 256],
+                      help='Specify a fixed bit width of vector to test')
+  parser.add_argument('--fixed-element-type', choices=element_types,
+                      help='Specify a fixed element type to test')
+  parser.add_argument('--triple',
+                      help='Specify a triple string to include in the IR')
+  args = parser.parse_args()
+
+  random.seed(args.seed)
+
+  if args.fixed_element_type is not None:
+    element_types=[args.fixed_element_type]
+
+  if args.fixed_bit_width is not None:
+    if args.fixed_bit_width == 128:
+      width_map={'i64': 2, 'i32': 4, 'i16': 8, 'i8': 16, 'f64': 2, 'f32': 4}
+      (width, element_type) = random.choice(
+          [(width_map[t], t) for t in element_types])
+    elif args.fixed_bit_width == 256:
+      width_map={'i64': 4, 'i32': 8, 'i16': 16, 'i8': 32, 'f64': 4, 'f32': 8}
+      (width, element_type) = random.choice(
+          [(width_map[t], t) for t in element_types])
+    else:
+      sys.exit(1) # Checked above by argument parsing.
+  else:
+    width = random.choice([2, 4, 8, 16, 32, 64])
+    element_type = random.choice(element_types)
+
+  element_modulus = {
+      'i8': 1 << 8, 'i16': 1 << 16, 'i32': 1 << 32, 'i64': 1 << 64,
+      'f32': 1 << 32, 'f64': 1 << 64}[element_type]
+
+  shuffle_range = (2 * width) if args.blends else width
+
+  # Because undef (-1) saturates and is indistinguishable when testing the
+  # correctness of a shuffle, we want to bias our fuzz toward having a decent
+  # mixture of non-undef lanes in the end. With a deep shuffle tree, the
+  # probabilies aren't good so we need to bias things. The math here is that if
+  # we uniformly select between -1 and the other inputs, each element of the
+  # result will have the following probability of being undef:
+  #
+  #   1 - (shuffle_range/(shuffle_range+1))^max_shuffle_height
+  #
+  # More generally, for any probability P of selecting a defined element in
+  # a single shuffle, the end result is:
+  #
+  #   1 - P^max_shuffle_height
+  #
+  # The power of the shuffle height is the real problem, as we want:
+  #
+  #   1 - shuffle_range/(shuffle_range+1)
+  #
+  # So we bias the selection of undef at any given node based on the tree
+  # height. Below, let 'A' be 'len(shuffle_range)', 'C' be 'max_shuffle_height',
+  # and 'B' be the bias we use to compensate for
+  # C '((A+1)*A^(1/C))/(A*(A+1)^(1/C))':
+  #
+  #   1 - (B * A)/(A + 1)^C = 1 - A/(A + 1)
+  #
+  # So at each node we use:
+  #
+  #   1 - (B * A)/(A + 1)
+  # = 1 - ((A + 1) * A * A^(1/C))/(A * (A + 1) * (A + 1)^(1/C))
+  # = 1 - ((A + 1) * A^((C + 1)/C))/(A * (A + 1)^((C + 1)/C))
+  #
+  # This is the formula we use to select undef lanes in the shuffle.
+  A = float(shuffle_range)
+  C = float(args.max_shuffle_height)
+  undef_prob = 1.0 - (((A + 1.0) * pow(A, (C + 1.0)/C)) /
+                      (A * pow(A + 1.0, (C + 1.0)/C)))
+
+  shuffle_tree = [[[-1 if random.random() <= undef_prob
+                       else random.choice(range(shuffle_range))
+                    for _ in itertools.repeat(None, width)]
+                   for _ in itertools.repeat(None, args.max_shuffle_height - i)]
+                  for i in range(args.max_shuffle_height)]
+
+  if args.verbose:
+    # Print out the shuffle sequence in a compact form.
+    print(('Testing shuffle sequence "%s" (v%d%s):' %
+                         (args.seed, width, element_type)), file=sys.stderr)
+    for i, shuffles in enumerate(shuffle_tree):
+      print('  tree level %d:' % (i,), file=sys.stderr)
+      for j, s in enumerate(shuffles):
+        print('    shuffle %d: %s' % (j, s), file=sys.stderr)
+    print('', file=sys.stderr)
+
+  # Symbolically evaluate the shuffle tree.
+  inputs = [[int(j % element_modulus)
+             for j in range(i * width + 1, (i + 1) * width + 1)]
+            for i in range(args.max_shuffle_height + 1)]
+  results = inputs
+  for shuffles in shuffle_tree:
+    results = [[((results[i] if j < width else results[i + 1])[j % width]
+                 if j != -1 else -1)
+                for j in s]
+               for i, s in enumerate(shuffles)]
+  if len(results) != 1:
+    print('ERROR: Bad results: %s' % (results,), file=sys.stderr)
+    sys.exit(1)
+  result = results[0]
+
+  if args.verbose:
+    print('Which transforms:', file=sys.stderr)
+    print('  from: %s' % (inputs,), file=sys.stderr)
+    print('  into: %s' % (result,), file=sys.stderr)
+    print('', file=sys.stderr)
+
+  # The IR uses silly names for floating point types. We also need a same-size
+  # integer type.
+  integral_element_type = element_type
+  if element_type == 'f32':
+    integral_element_type = 'i32'
+    element_type = 'float'
+  elif element_type == 'f64':
+    integral_element_type = 'i64'
+    element_type = 'double'
+
+  # Now we need to generate IR for the shuffle function.
+  subst = {'N': width, 'T': element_type, 'IT': integral_element_type}
+  print("""
+define internal fastcc <%(N)d x %(T)s> @test(%(arguments)s) noinline nounwind {
+entry:""" % dict(subst,
+                 arguments=', '.join(
+                     ['<%(N)d x %(T)s> %%s.0.%(i)d' % dict(subst, i=i)
+                      for i in range(args.max_shuffle_height + 1)])))
+
+  for i, shuffles in enumerate(shuffle_tree):
+   for j, s in enumerate(shuffles):
+    print("""
+  %%s.%(next_i)d.%(j)d = shufflevector <%(N)d x %(T)s> %%s.%(i)d.%(j)d, <%(N)d x %(T)s> %%s.%(i)d.%(next_j)d, <%(N)d x i32> <%(S)s>
+""".strip('\n') % dict(subst, i=i, next_i=i + 1, j=j, next_j=j + 1,
+                       S=', '.join(['i32 ' + (str(si) if si != -1 else 'undef')
+                                    for si in s])))
+
+  print("""
+  ret <%(N)d x %(T)s> %%s.%(i)d.0
+}
+""" % dict(subst, i=len(shuffle_tree)))
+
+  # Generate some string constants that we can use to report errors.
+  for i, r in enumerate(result):
+    if r != -1:
+      s = ('FAIL(%(seed)s): lane %(lane)d, expected %(result)d, found %%d\n\\0A' %
+           {'seed': args.seed, 'lane': i, 'result': r})
+      s += ''.join(['\\00' for _ in itertools.repeat(None, 128 - len(s) + 2)])
+      print("""
+@error.%(i)d = private unnamed_addr global [128 x i8] c"%(s)s"
+""".strip() % {'i': i, 's': s})
+
+  # Define a wrapper function which is marked 'optnone' to prevent
+  # interprocedural optimizations from deleting the test.
+  print("""
+define internal fastcc <%(N)d x %(T)s> @test_wrapper(%(arguments)s) optnone noinline {
+  %%result = call fastcc <%(N)d x %(T)s> @test(%(arguments)s)
+  ret <%(N)d x %(T)s> %%result
+}
+""" % dict(subst,
+           arguments=', '.join(['<%(N)d x %(T)s> %%s.%(i)d' % dict(subst, i=i)
+                                for i in range(args.max_shuffle_height + 1)])))
+
+  # Finally, generate a main function which will trap if any lanes are mapped
+  # incorrectly (in an observable way).
+  print("""
+define i32 @main() {
+entry:
+  ; Create a scratch space to print error messages.
+  %%str = alloca [128 x i8]
+  %%str.ptr = getelementptr inbounds [128 x i8], [128 x i8]* %%str, i32 0, i32 0
+
+  ; Build the input vector and call the test function.
+  %%v = call fastcc <%(N)d x %(T)s> @test_wrapper(%(inputs)s)
+  ; We need to cast this back to an integer type vector to easily check the
+  ; result.
+  %%v.cast = bitcast <%(N)d x %(T)s> %%v to <%(N)d x %(IT)s>
+  br label %%test.0
+""" % dict(subst,
+           inputs=', '.join(
+               [('<%(N)d x %(T)s> bitcast '
+                 '(<%(N)d x %(IT)s> <%(input)s> to <%(N)d x %(T)s>)' %
+                 dict(subst, input=', '.join(['%(IT)s %(i)d' % dict(subst, i=i)
+                                              for i in input])))
+                for input in inputs])))
+
+  # Test that each non-undef result lane contains the expected value.
+  for i, r in enumerate(result):
+    if r == -1:
+      print("""
+test.%(i)d:
+  ; Skip this lane, its value is undef.
+  br label %%test.%(next_i)d
+""" % dict(subst, i=i, next_i=i + 1))
+    else:
+      print("""
+test.%(i)d:
+  %%v.%(i)d = extractelement <%(N)d x %(IT)s> %%v.cast, i32 %(i)d
+  %%cmp.%(i)d = icmp ne %(IT)s %%v.%(i)d, %(r)d
+  br i1 %%cmp.%(i)d, label %%die.%(i)d, label %%test.%(next_i)d
+
+die.%(i)d:
+  ; Capture the actual value and print an error message.
+  %%tmp.%(i)d = zext %(IT)s %%v.%(i)d to i2048
+  %%bad.%(i)d = trunc i2048 %%tmp.%(i)d to i32
+  call i32 (i8*, i8*, ...) @sprintf(i8* %%str.ptr, i8* getelementptr inbounds ([128 x i8], [128 x i8]* @error.%(i)d, i32 0, i32 0), i32 %%bad.%(i)d)
+  %%length.%(i)d = call i32 @strlen(i8* %%str.ptr)
+  call i32 @write(i32 2, i8* %%str.ptr, i32 %%length.%(i)d)
+  call void @llvm.trap()
+  unreachable
+""" % dict(subst, i=i, next_i=i + 1, r=r))
+
+  print("""
+test.%d:
+  ret i32 0
+}
+
+declare i32 @strlen(i8*)
+declare i32 @write(i32, i8*, i32)
+declare i32 @sprintf(i8*, i8*, ...)
+declare void @llvm.trap() noreturn nounwind
+""" % (len(result),))
+
+if __name__ == '__main__':
+  main()