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Diffstat (limited to 'utils/shuffle_fuzz.py')
| -rwxr-xr-x | utils/shuffle_fuzz.py | 256 |
1 files changed, 256 insertions, 0 deletions
diff --git a/utils/shuffle_fuzz.py b/utils/shuffle_fuzz.py new file mode 100755 index 0000000..384a93a --- /dev/null +++ b/utils/shuffle_fuzz.py @@ -0,0 +1,256 @@ +#!/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. +""" + +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 xrange(args.max_shuffle_height)] + + if args.verbose: + # Print out the shuffle sequence in a compact form. + print >>sys.stderr, ('Testing shuffle sequence "%s" (v%d%s):' % + (args.seed, width, element_type)) + for i, shuffles in enumerate(shuffle_tree): + print >>sys.stderr, ' tree level %d:' % (i,) + for j, s in enumerate(shuffles): + print >>sys.stderr, ' shuffle %d: %s' % (j, s) + print >>sys.stderr, '' + + # Symbolically evaluate the shuffle tree. + inputs = [[int(j % element_modulus) + for j in xrange(i * width + 1, (i + 1) * width + 1)] + for i in xrange(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 >>sys.stderr, 'ERROR: Bad results: %s' % (results,) + sys.exit(1) + result = results[0] + + if args.verbose: + print >>sys.stderr, 'Which transforms:' + print >>sys.stderr, ' from: %s' % (inputs,) + print >>sys.stderr, ' into: %s' % (result,) + print >>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 xrange(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\\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 xrange(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]* %%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]* @error.%(i)d, i32 0, i32 0), i32 %%bad.%(i)d) + %%length.%(i)d = call i32 @strlen(i8* %%str.ptr) + %%size.%(i)d = add i32 %%length.%(i)d, 1 + call i32 @write(i32 2, i8* %%str.ptr, i32 %%size.%(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() |