Reland "[regexp] Bytecode peephole optimization"

This is a reland of 66129430

Fixed: Unaligned reads, unspecified evaluation order.

Original change's description:
> [regexp] Bytecode peephole optimization
>
> Bytecodes used by the regular expression interpreter often occur in
> specific sequences. The number of dispatches in the interpreter can be
> reduced if those sequences are combined into a single bytecode.
>
> This CL adds a peephole optimization pass for regexp bytecodes.
> This pass checks the generated bytecode for pre-defined sequences that
> can be merged into a single bytecode.
>
> With the currently implemented bytecode sequences a speedup of 1.12x on
> regex-dna and octane-regexp is achieved.
>
> Bug: v8:9330
> Change-Id: I827f93273a5848e5963c7e3329daeb898995d151
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1813743
> Commit-Queue: Patrick Thier <pthier@google.com>
> Reviewed-by: Peter Marshall <petermarshall@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#63992}

Cq-Include-Trybots: luci.v8.try:v8_linux64_ubsan_rel_ng
Cq-Include-Trybots: luci.v8.try:v8_linux_gcc_rel
Bug: v8:9330,chromium:1008502,chromium:1008631
Change-Id: Ib9fc395b6809aa1debdb54d9fba5b7f09a235e5b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1828917Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64064}

BUILD.gn

@@ -2778,6 +2778,9 @@ v8_source_set("v8_base_without_compiler") {
     "src/regexp/regexp-bytecode-generator-inl.h",
     "src/regexp/regexp-bytecode-generator.cc",
     "src/regexp/regexp-bytecode-generator.h",
+    "src/regexp/regexp-bytecode-peephole.cc",
+    "src/regexp/regexp-bytecode-peephole.h",
+    "src/regexp/regexp-bytecodes.cc",
     "src/regexp/regexp-bytecodes.h",
     "src/regexp/regexp-compiler-tonode.cc",
     "src/regexp/regexp-compiler.cc",

src/flags/flag-definitions.h

@@ -1274,6 +1274,15 @@ DEFINE_BOOL(regexp_tier_up, true,
 DEFINE_INT(regexp_tier_up_ticks, 1,
            "set the number of executions for the regexp interpreter before "
            "tiering-up to the compiler")
+DEFINE_BOOL(regexp_peephole_optimization, true,
+            "enable peephole optimization for regexp bytecode")
+DEFINE_BOOL(trace_regexp_peephole_optimization, false,
+            "trace regexp bytecode peephole optimization")
+DEFINE_BOOL(trace_regexp_bytecodes, false, "trace regexp bytecode execution")
+DEFINE_BOOL(trace_regexp_assembler, false,
+            "trace regexp macro assembler calls.")
+DEFINE_BOOL(trace_regexp_parser, false, "trace regexp parsing")
+DEFINE_BOOL(trace_regexp_tier_up, false, "trace regexp tiering up execution")
 
 // Testing flags test/cctest/test-{flags,api,serialization}.cc
 DEFINE_BOOL(testing_bool_flag, true, "testing_bool_flag")
@@ -1408,11 +1417,6 @@ DEFINE_BOOL(trace_isolates, false, "trace isolate state changes")
 // Regexp
 DEFINE_BOOL(regexp_possessive_quantifier, false,
             "enable possessive quantifier syntax for testing")
-DEFINE_BOOL(trace_regexp_bytecodes, false, "trace regexp bytecode execution")
-DEFINE_BOOL(trace_regexp_assembler, false,
-            "trace regexp macro assembler calls.")
-DEFINE_BOOL(trace_regexp_parser, false, "trace regexp parsing")
-DEFINE_BOOL(trace_regexp_tier_up, false, "trace regexp tiering up execution")
 
 // Debugger
 DEFINE_BOOL(print_break_location, false, "print source location on debug break")

src/regexp/regexp-bytecode-generator.cc

@@ -7,6 +7,7 @@
 #include "src/ast/ast.h"
 #include "src/objects/objects-inl.h"
 #include "src/regexp/regexp-bytecode-generator-inl.h"
+#include "src/regexp/regexp-bytecode-peephole.h"
 #include "src/regexp/regexp-bytecodes.h"
 #include "src/regexp/regexp-macro-assembler.h"
 
@@ -18,6 +19,7 @@ RegExpBytecodeGenerator::RegExpBytecodeGenerator(Isolate* isolate, Zone* zone)
       buffer_(Vector<byte>::New(1024)),
       pc_(0),
       advance_current_end_(kInvalidPC),
+      jump_edges_(zone),
       isolate_(isolate) {}
 
 RegExpBytecodeGenerator::~RegExpBytecodeGenerator() {
@@ -39,6 +41,7 @@ void RegExpBytecodeGenerator::Bind(Label* l) {
       int fixup = pos;
       pos = *reinterpret_cast<int32_t*>(buffer_.begin() + fixup);
       *reinterpret_cast<uint32_t*>(buffer_.begin() + fixup) = pc_;
+      jump_edges_.emplace(fixup, pc_);
     }
   }
   l->bind_to(pc_);
@@ -46,16 +49,17 @@ void RegExpBytecodeGenerator::Bind(Label* l) {
 
 void RegExpBytecodeGenerator::EmitOrLink(Label* l) {
   if (l == nullptr) l = &backtrack_;
+  int pos = 0;
   if (l->is_bound()) {
-    Emit32(l->pos());
+    pos = l->pos();
+    jump_edges_.emplace(pc_, pos);
   } else {
-    int pos = 0;
     if (l->is_linked()) {
       pos = l->pos();
     }
     l->link_to(pc_);
-    Emit32(pos);
   }
+  Emit32(pos);
 }
 
 void RegExpBytecodeGenerator::PopRegister(int register_index) {
@@ -365,8 +369,16 @@ void RegExpBytecodeGenerator::IfRegisterEqPos(int register_index,
 Handle<HeapObject> RegExpBytecodeGenerator::GetCode(Handle<String> source) {
   Bind(&backtrack_);
   Emit(BC_POP_BT, 0);
-  Handle<ByteArray> array = isolate_->factory()->NewByteArray(length());
-  Copy(array->GetDataStartAddress());
+
+  Handle<ByteArray> array;
+  if (FLAG_regexp_peephole_optimization) {
+    array = RegExpBytecodePeepholeOptimization::OptimizeBytecode(
+        isolate_, zone(), source, buffer_.begin(), length(), jump_edges_);
+  } else {
+    array = isolate_->factory()->NewByteArray(length());
+    Copy(array->GetDataStartAddress());
+  }
+
   return array;
 }
 

src/regexp/regexp-bytecode-generator.h

@@ -100,6 +100,12 @@ class V8_EXPORT_PRIVATE RegExpBytecodeGenerator : public RegExpMacroAssembler {
   int advance_current_offset_;
   int advance_current_end_;
 
+  // Stores jump edges emitted for the bytecode (used by
+  // RegExpBytecodePeepholeOptimization).
+  // Key: jump source (offset in buffer_ where jump destination is stored).
+  // Value: jump destination (offset in buffer_ to jump to).
+  ZoneUnorderedMap<int, int> jump_edges_;
+
   Isolate* isolate_;
 
   static const int kInvalidPC = -1;

src/regexp/regexp-bytecode-peephole.h

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_REGEXP_REGEXP_BYTECODE_PEEPHOLE_H_
+#define V8_REGEXP_REGEXP_BYTECODE_PEEPHOLE_H_
+
+#include "src/common/globals.h"
+#include "src/zone/zone-containers.h"
+
+namespace v8 {
+namespace internal {
+
+class ByteArray;
+
+// Peephole optimization for regexp interpreter bytecode.
+// Pre-defined bytecode sequences occuring in the bytecode generated by the
+// RegExpBytecodeGenerator can be optimized into a single bytecode.
+class RegExpBytecodePeepholeOptimization : public AllStatic {
+ public:
+  // Performs peephole optimization on the given bytecode and returns the
+  // optimized bytecode.
+  static Handle<ByteArray> OptimizeBytecode(
+      Isolate* isolate, Zone* zone, Handle<String> source, const byte* bytecode,
+      int length, const ZoneUnorderedMap<int, int>& jump_edges);
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_REGEXP_REGEXP_BYTECODE_PEEPHOLE_H_

src/regexp/regexp-bytecodes.cc

+// Copyright 2019 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/regexp/regexp-bytecodes.h"
+
+#include <cctype>
+
+#include "src/utils/utils.h"
+
+namespace v8 {
+namespace internal {
+
+void RegExpBytecodeDisassembleSingle(const byte* code_base, const byte* pc) {
+  PrintF("%s", RegExpBytecodeName(*pc));
+
+  // Args and the bytecode as hex.
+  for (int i = 0; i < RegExpBytecodeLength(*pc); i++) {
+    PrintF(", %02x", pc[i]);
+  }
+  PrintF(" ");
+
+  // Args as ascii.
+  for (int i = 1; i < RegExpBytecodeLength(*pc); i++) {
+    unsigned char b = pc[i];
+    PrintF("%c", std::isprint(b) ? b : '.');
+  }
+  PrintF("\n");
+}
+
+void RegExpBytecodeDisassemble(const byte* code_base, int length,
+                               const char* pattern) {
+  PrintF("[generated bytecode for regexp pattern: '%s']\n", pattern);
+
+  ptrdiff_t offset = 0;
+
+  while (offset < length) {
+    const byte* const pc = code_base + offset;
+    PrintF("%p  %4" V8PRIxPTRDIFF "  ", pc, offset);
+    RegExpBytecodeDisassembleSingle(code_base, pc);
+    offset += RegExpBytecodeLength(*pc);
+  }
+}
+
+}  // namespace internal
+}  // namespace v8

src/regexp/regexp-interpreter.cc

@@ -64,23 +64,6 @@ bool BackRefMatchesNoCase(Isolate* isolate, int from, int current, int len,
   return true;
 }
 
-void DisassembleSingleBytecode(const byte* code_base, const byte* pc) {
-  PrintF("%s", RegExpBytecodeName(*pc));
-
-  // Args and the bytecode as hex.
-  for (int i = 0; i < RegExpBytecodeLength(*pc); i++) {
-    PrintF(", %02x", pc[i]);
-  }
-  PrintF(" ");
-
-  // Args as ascii.
-  for (int i = 1; i < RegExpBytecodeLength(*pc); i++) {
-    unsigned char b = pc[i];
-    PrintF("%c", std::isprint(b) ? b : '.');
-  }
-  PrintF("\n");
-}
-
 #ifdef DEBUG
 void MaybeTraceInterpreter(const byte* code_base, const byte* pc,
                            int stack_depth, int current_position,
@@ -95,7 +78,7 @@ void MaybeTraceInterpreter(const byte* code_base, const byte* pc,
     PrintF(format, pc - code_base, stack_depth, current_position, current_char,
            printable ? current_char : '.');
 
-    DisassembleSingleBytecode(code_base, pc);
+    RegExpBytecodeDisassembleSingle(code_base, pc);
   }
 }
 #endif  // DEBUG
@@ -257,6 +240,13 @@ IrregexpInterpreter::Result HandleInterrupts(
   return IrregexpInterpreter::SUCCESS;
 }
 
+bool CheckBitInTable(const uint32_t current_char, const byte* const table) {
+  int mask = RegExpMacroAssembler::kTableMask;
+  int b = table[(current_char & mask) >> kBitsPerByteLog2];
+  int bit = (current_char & (kBitsPerByte - 1));
+  return (b & (1 << bit)) != 0;
+}
+
 // If computed gotos are supported by the compiler, we can get addresses to
 // labels directly in C/C++. Every bytecode handler has its own label and we
 // store the addresses in a dispatch table indexed by bytecode. To execute the
@@ -281,7 +271,7 @@ IrregexpInterpreter::Result HandleInterrupts(
 #define DISPATCH()  \
   pc = next_pc;     \
   insn = next_insn; \
-  break
+  goto switch_dispatch_continuation
 #endif  // V8_USE_COMPUTED_GOTO
 
 // ADVANCE/SET_PC_FROM_OFFSET are separated from DISPATCH, because ideally some
@@ -331,19 +321,13 @@ IrregexpInterpreter::Result RawMatch(Isolate* isolate, ByteArray code_array,
 // Fill dispatch table from last defined bytecode up to the next power of two
 // with BREAK (invalid operation).
 // TODO(pthier): Find a way to fill up automatically (at compile time)
-// 53 real bytecodes -> 11 fillers
+// 59 real bytecodes -> 5 fillers
 #define BYTECODE_FILLER_ITERATOR(V) \
   V(BREAK) /* 1 */                  \
   V(BREAK) /* 2 */                  \
   V(BREAK) /* 3 */                  \
   V(BREAK) /* 4 */                  \
-  V(BREAK) /* 5 */                  \
-  V(BREAK) /* 6 */                  \
-  V(BREAK) /* 7 */                  \
-  V(BREAK) /* 8 */                  \
-  V(BREAK) /* 9 */                  \
-  V(BREAK) /* 10 */                 \
-  V(BREAK) /* 11 */
+  V(BREAK) /* 5 */
 
 #define COUNT(...) +1
   static constexpr int kRegExpBytecodeFillerCount =
@@ -652,10 +636,7 @@ IrregexpInterpreter::Result RawMatch(Isolate* isolate, ByteArray code_array,
       DISPATCH();
     }
     BYTECODE(CHECK_BIT_IN_TABLE) {
-      int mask = RegExpMacroAssembler::kTableMask;
-      byte b = pc[8 + ((current_char & mask) >> kBitsPerByteLog2)];
-      int bit = (current_char & (kBitsPerByte - 1));
-      if ((b & (1 << bit)) != 0) {
+      if (CheckBitInTable(current_char, pc + 8)) {
         SET_PC_FROM_OFFSET(Load32Aligned(pc + 4));
       } else {
         ADVANCE(CHECK_BIT_IN_TABLE);
@@ -834,6 +815,118 @@ IrregexpInterpreter::Result RawMatch(Isolate* isolate, ByteArray code_array,
       }
       DISPATCH();
     }
+    BYTECODE(SKIP_UNTIL_CHAR) {
+      int load_offset = (insn >> BYTECODE_SHIFT);
+      uint32_t advance = Load16Aligned(pc + 4);
+      uint32_t c = Load16Aligned(pc + 6);
+      while (static_cast<uintptr_t>(current + load_offset) <
+             static_cast<uintptr_t>(subject.length())) {
+        current_char = subject[current + load_offset];
+        if (c == current_char) {
+          SET_PC_FROM_OFFSET(Load32Aligned(pc + 8));
+          DISPATCH();
+        }
+        current += advance;
+      }
+      SET_PC_FROM_OFFSET(Load32Aligned(pc + 12));
+      DISPATCH();
+    }
+    BYTECODE(SKIP_UNTIL_CHAR_AND) {
+      int load_offset = (insn >> BYTECODE_SHIFT);
+      uint16_t advance = Load16Aligned(pc + 4);
+      uint16_t c = Load16Aligned(pc + 6);
+      uint32_t mask = Load32Aligned(pc + 8);
+      int32_t maximum_offset = Load32Aligned(pc + 12);
+      while (static_cast<uintptr_t>(current + maximum_offset) <=
+             static_cast<uintptr_t>(subject.length())) {
+        current_char = subject[current + load_offset];
+        if (c == (current_char & mask)) {
+          SET_PC_FROM_OFFSET(Load32Aligned(pc + 16));
+          DISPATCH();
+        }
+        current += advance;
+      }
+      SET_PC_FROM_OFFSET(Load32Aligned(pc + 20));
+      DISPATCH();
+    }
+    BYTECODE(SKIP_UNTIL_CHAR_POS_CHECKED) {
+      int load_offset = (insn >> BYTECODE_SHIFT);
+      uint16_t advance = Load16Aligned(pc + 4);
+      uint16_t c = Load16Aligned(pc + 6);
+      int32_t maximum_offset = Load32Aligned(pc + 8);
+      while (static_cast<uintptr_t>(current + maximum_offset) <=
+             static_cast<uintptr_t>(subject.length())) {
+        current_char = subject[current + load_offset];
+        if (c == current_char) {
+          SET_PC_FROM_OFFSET(Load32Aligned(pc + 12));
+          DISPATCH();
+        }
+        current += advance;
+      }
+      SET_PC_FROM_OFFSET(Load32Aligned(pc + 16));
+      DISPATCH();
+    }
+    BYTECODE(SKIP_UNTIL_BIT_IN_TABLE) {
+      int load_offset = (insn >> BYTECODE_SHIFT);
+      uint32_t advance = Load16Aligned(pc + 4);
+      const byte* table = pc + 8;
+      while (static_cast<uintptr_t>(current + load_offset) <
+             static_cast<uintptr_t>(subject.length())) {
+        current_char = subject[current + load_offset];
+        if (CheckBitInTable(current_char, table)) {
+          SET_PC_FROM_OFFSET(Load32Aligned(pc + 24));
+          DISPATCH();
+        }
+        current += advance;
+      }
+      SET_PC_FROM_OFFSET(Load32Aligned(pc + 28));
+      DISPATCH();
+    }
+    BYTECODE(SKIP_UNTIL_GT_OR_NOT_BIT_IN_TABLE) {
+      int load_offset = (insn >> BYTECODE_SHIFT);
+      uint16_t advance = Load16Aligned(pc + 4);
+      uint16_t limit = Load16Aligned(pc + 6);
+      const byte* table = pc + 8;
+      while (static_cast<uintptr_t>(current + load_offset) <
+             static_cast<uintptr_t>(subject.length())) {
+        current_char = subject[current + load_offset];
+        if (current_char > limit) {
+          SET_PC_FROM_OFFSET(Load32Aligned(pc + 24));
+          DISPATCH();
+        }
+        if (!CheckBitInTable(current_char, table)) {
+          SET_PC_FROM_OFFSET(Load32Aligned(pc + 24));
+          DISPATCH();
+        }
+        current += advance;
+      }
+      SET_PC_FROM_OFFSET(Load32Aligned(pc + 28));
+      DISPATCH();
+    }
+    BYTECODE(SKIP_UNTIL_CHAR_OR_CHAR) {
+      int load_offset = (insn >> BYTECODE_SHIFT);
+      uint32_t advance = Load32Aligned(pc + 4);
+      uint16_t c = Load16Aligned(pc + 8);
+      uint16_t c2 = Load16Aligned(pc + 10);
+      while (static_cast<uintptr_t>(current + load_offset) <
+             static_cast<uintptr_t>(subject.length())) {
+        current_char = subject[current + load_offset];
+        // The two if-statements below are split up intentionally, as combining
+        // them seems to result in register allocation behaving quite
+        // differently and slowing down the resulting code.
+        if (c == current_char) {
+          SET_PC_FROM_OFFSET(Load32Aligned(pc + 12));
+          DISPATCH();
+        }
+        if (c2 == current_char) {
+          SET_PC_FROM_OFFSET(Load32Aligned(pc + 12));
+          DISPATCH();
+        }
+        current += advance;
+      }
+      SET_PC_FROM_OFFSET(Load32Aligned(pc + 16));
+      DISPATCH();
+    }
 #if V8_USE_COMPUTED_GOTO
 // Lint gets confused a lot if we just use !V8_USE_COMPUTED_GOTO or ifndef
 // V8_USE_COMPUTED_GOTO here.
@@ -841,6 +934,9 @@ IrregexpInterpreter::Result RawMatch(Isolate* isolate, ByteArray code_array,
       default:
         UNREACHABLE();
     }
+  // Label we jump to in DISPATCH(). There must be no instructions between the
+  // end of the switch, this label and the end of the loop.
+  switch_dispatch_continuation : {}
 #endif  // V8_USE_COMPUTED_GOTO
   }
 }
@@ -855,25 +951,6 @@ IrregexpInterpreter::Result RawMatch(Isolate* isolate, ByteArray code_array,
 
 }  // namespace
 
-// static
-void IrregexpInterpreter::Disassemble(ByteArray byte_array,
-                                      const std::string& pattern) {
-  DisallowHeapAllocation no_gc;
-
-  PrintF("[generated bytecode for regexp pattern: '%s']\n", pattern.c_str());
-
-  const byte* const code_base = byte_array.GetDataStartAddress();
-  const int byte_array_length = byte_array.length();
-  ptrdiff_t offset = 0;
-
-  while (offset < byte_array_length) {
-    const byte* const pc = code_base + offset;
-    PrintF("%p  %4" V8PRIxPTRDIFF "  ", pc, offset);
-    DisassembleSingleBytecode(code_base, pc);
-    offset += RegExpBytecodeLength(*pc);
-  }
-}
-
 // static
 IrregexpInterpreter::Result IrregexpInterpreter::Match(
     Isolate* isolate, JSRegExp regexp, String subject_string, int* registers,

src/regexp/regexp-interpreter.h

@@ -46,8 +46,6 @@ class V8_EXPORT_PRIVATE IrregexpInterpreter : public AllStatic {
                               int registers_length, int start_position,
                               RegExp::CallOrigin call_origin);
 
-  static void Disassemble(ByteArray byte_array, const std::string& pattern);
-
  private:
   static Result Match(Isolate* isolate, JSRegExp regexp, String subject_string,
                       int* registers, int registers_length, int start_position,

src/regexp/regexp.cc

@@ -9,6 +9,7 @@
 #include "src/heap/heap-inl.h"
 #include "src/objects/js-regexp-inl.h"
 #include "src/regexp/regexp-bytecode-generator.h"
+#include "src/regexp/regexp-bytecodes.h"
 #include "src/regexp/regexp-compiler.h"
 #include "src/regexp/regexp-dotprinter.h"
 #include "src/regexp/regexp-interpreter.h"
@@ -881,7 +882,8 @@ bool RegExpImpl::Compile(Isolate* isolate, Zone* zone, RegExpCompileData* data,
         data->compilation_target == RegExpCompilationTarget::kBytecode) {
       Handle<ByteArray> bytecode(ByteArray::cast(result.code), isolate);
       auto pattern_cstring = pattern->ToCString();
-      IrregexpInterpreter::Disassemble(*bytecode, pattern_cstring.get());
+      RegExpBytecodeDisassemble(bytecode->GetDataStartAddress(),
+                                bytecode->length(), pattern_cstring.get());
     }
   }
 

tools/regexp-sequences.py

+#!/usr/bin/env python
+# Copyright 2019 the V8 project authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""
+python %prog trace-file
+
+Parses output generated by v8 with flag --trace-regexp-bytecodes and generates
+a list of the most common sequences.
+"""
+
+from __future__ import print_function
+
+import sys
+import re
+import collections
+
+def parse(file, seqlen):
+  # example:
+  # pc = 00, sp = 0, curpos = 0, curchar = 0000000a ..., bc = PUSH_BT, 02, 00, 00, 00, e8, 00, 00, 00 .......
+  rx = re.compile(r'pc = (?P<pc>[0-9a-f]+), sp = (?P<sp>\d+), '
+                  r'curpos = (?P<curpos>\d+), curchar = (?P<char_hex>[0-9a-f]+) '
+                  r'(:?\.|\()(?P<char>\.|\w)(:?\.|\)), bc = (?P<bc>\w+), .*')
+  total = 0
+  bc_cnt = [None] * seqlen
+  for i in xrange(seqlen):
+    bc_cnt[i] = {}
+  last = [None] * seqlen
+  with open(file) as f:
+    l = f.readline()
+    while l:
+      l = l.strip()
+      if l.startswith("Start bytecode interpreter"):
+        for i in xrange(seqlen):
+          last[i] = collections.deque(maxlen=i+1)
+
+      match = rx.search(l)
+      if match:
+        total += 1
+        bc = match.group('bc')
+        for i in xrange(seqlen):
+          last[i].append(bc)
+          key = ' --> '.join(last[i])
+          bc_cnt[i][key] = bc_cnt[i].get(key,0) + 1
+
+      l = f.readline()
+  return bc_cnt, total
+
+def print_most_common(d, seqlen, total):
+  sorted_d = sorted(d.items(), key=lambda kv: kv[1], reverse=True)
+  for (k,v) in sorted_d:
+    if v*100/total < 1.0:
+      return
+    print("{}: {} ({} %)".format(k,v,(v*100/total)))
+
+def main(argv):
+  max_seq = 7
+  bc_cnt, total = parse(argv[1],max_seq)
+  for i in xrange(max_seq):
+    print()
+    print("Most common of length {}".format(i+1))
+    print()
+    print_most_common(bc_cnt[i], i, total)
+
+if __name__ == '__main__':
+  main(sys.argv)