Revert "[vm] Switch datastream Write/WriteUnsigned to (S)LEB128."

This reverts commit 80102c981b.

Reason for revert: b/186359854

Original change's description:
> [vm] Switch datastream Write/WriteUnsigned to (S)LEB128.
>
> This reduces the number of variable-length integer encodings in our
> database from 2 to 1, and chooses the more standard one.
>
> TEST=Existing tests, in particular any that involve snapshots.
>
> Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-asan-linux-release-x64-try,vm-kernel-precomp-dwarf-linux-product-x64-try,vm-kernel-precomp-msan-linux-release-x64-try,vm-kernel-precomp-ubsan-linux-release-x64-try,vm-kernel-precomp-tsan-linux-release-x64-try,vm-kernel-precomp-nnbd-linux-debug-x64-try,vm-kernel-precomp-nnbd-linux-debug-simarm_x64-try,vm-kernel-precomp-linux-debug-simarm64c-try,vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64c-try,vm-kernel-precomp-linux-product-x64-try,vm-kernel-precomp-linux-release-x64-try
> Change-Id: Ia700158ac873ad32ac28c1027a669895961bc715
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196321
> Commit-Queue: Tess Strickland <sstrickl@google.com>
> Reviewed-by: Ryan Macnak <rmacnak@google.com>
> Reviewed-by: Martin Kustermann <kustermann@google.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Idf32bdd879cf8bb7407f6dae764312140ad6eeb2
Cq-Include-Trybots: luci.dart.try:vm-kernel-precomp-asan-linux-release-x64-try,vm-kernel-precomp-dwarf-linux-product-x64-try,vm-kernel-precomp-msan-linux-release-x64-try,vm-kernel-precomp-ubsan-linux-release-x64-try,vm-kernel-precomp-tsan-linux-release-x64-try,vm-kernel-precomp-nnbd-linux-debug-x64-try,vm-kernel-precomp-nnbd-linux-debug-simarm_x64-try,vm-kernel-precomp-linux-debug-simarm64c-try,vm-kernel-precomp-linux-debug-simarm_x64-try,vm-kernel-precomp-linux-debug-x64-try,vm-kernel-precomp-linux-debug-x64c-try,vm-kernel-precomp-linux-product-x64-try,vm-kernel-precomp-linux-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196920
Reviewed-by: Ivan Inozemtsev <iinozemtsev@google.com>
Commit-Queue: Ivan Inozemtsev <iinozemtsev@google.com>

runtime/platform/utils.h

@@ -395,23 +395,29 @@ class Utils {
     return ((-0x20000000000000LL <= value) && (value <= 0x20000000000000LL));
   }
 
+  static constexpr uword NBitMaskUnsafe(uint32_t n) {
+    static_assert((sizeof(uword) * kBitsPerByte) == kBitsPerWord,
+                  "Unexpected uword size");
+    return n == kBitsPerWord ? std::numeric_limits<uword>::max()
+                             : (static_cast<uword>(1) << n) - 1;
+  }
+
   // The lowest n bits are 1, the others are 0.
-  template <typename T = uword>
+  static uword NBitMask(uint32_t n) {
-  static constexpr T NBitMask(size_t n) {
+    ASSERT(n <= kBitsPerWord);
-    static_assert(std::is_integral<T>::value, "Must be integral type");
+    return NBitMaskUnsafe(n);
-    using Unsigned = typename std::make_unsigned<T>::type;
+  }
-    assert(n <= sizeof(T) * kBitsPerByte);
+
-    return n == sizeof(T) * kBitsPerByte
+  static word SignedNBitMask(uint32_t n) {
-               ? static_cast<T>(-1)
+    uword mask = NBitMask(n);
-               : static_cast<T>((static_cast<Unsigned>(1) << n) - 1);
+    return bit_cast<word>(mask);
   }
 
   template <typename T = uword>
-  static constexpr T Bit(size_t n) {
+  static T Bit(uint32_t n) {
-    static_assert(std::is_integral<T>::value, "Must be integral type");
+    ASSERT(n < sizeof(T) * kBitsPerByte);
-    using Unsigned = typename std::make_unsigned<T>::type;
+    T bit = 1;
-    assert(n < sizeof(T) * kBitsPerByte);
+    return bit << n;
-    return static_cast<T>(static_cast<Unsigned>(1) << n);
   }
 
   template <typename T>

runtime/vm/code_descriptors.cc

@@ -54,8 +54,8 @@ void DescriptorList::AddDescriptor(UntaggedPcDescriptors::Kind kind,
         UntaggedPcDescriptors::KindAndMetadata::Encode(kind, try_index,
                                                        yield_index);
 
-    encoded_data_.Write(kind_and_metadata);
+    encoded_data_.WriteSLEB128(kind_and_metadata);
-    encoded_data_.Write(pc_offset - prev_pc_offset);
+    encoded_data_.WriteSLEB128(pc_offset - prev_pc_offset);
     prev_pc_offset = pc_offset;
 
     if (!FLAG_precompiled_mode) {
@@ -80,8 +80,8 @@ void DescriptorList::AddDescriptor(UntaggedPcDescriptors::Kind kind,
         }
       }
       const int32_t encoded_pos = token_pos.Serialize();
-      encoded_data_.Write(deopt_id - prev_deopt_id);
+      encoded_data_.WriteSLEB128(deopt_id - prev_deopt_id);
-      encoded_data_.Write(
+      encoded_data_.WriteSLEB128(
           Utils::SubWithWrapAround(encoded_pos, prev_token_pos));
       prev_deopt_id = deopt_id;
       prev_token_pos = encoded_pos;
@@ -106,9 +106,9 @@ void CompressedStackMapsBuilder::AddEntry(intptr_t pc_offset,
   const uword pc_delta = pc_offset - last_pc_offset_;
   const uword non_spill_slot_bit_count =
       bitmap->Length() - spill_slot_bit_count;
-  encoded_bytes_.WriteUnsigned(pc_delta);
+  encoded_bytes_.WriteLEB128(pc_delta);
-  encoded_bytes_.WriteUnsigned(spill_slot_bit_count);
+  encoded_bytes_.WriteLEB128(spill_slot_bit_count);
-  encoded_bytes_.WriteUnsigned(non_spill_slot_bit_count);
+  encoded_bytes_.WriteLEB128(non_spill_slot_bit_count);
   bitmap->AppendAsBytesTo(&encoded_bytes_);
   last_pc_offset_ = pc_offset;
 }

runtime/vm/code_descriptors.h

@@ -209,7 +209,7 @@ struct CodeSourceMapOps : AllStatic {
   using ArgField = BitField<int32_t, int32_t, OpField::kNextBit>;
 
   static constexpr int32_t kMaxArgValue =
-      Utils::NBitMask(ArgField::bitsize() - 1);
+      Utils::NBitMaskUnsafe(ArgField::bitsize() - 1);
   static constexpr int32_t kMinArgValue = ~kMaxArgValue;
   static constexpr int32_t kSignBits = static_cast<uint32_t>(kMinArgValue) << 1;
 };

runtime/vm/compiler/backend/il_arm.cc

@@ -778,8 +778,8 @@ LocationSummary* AssertAssignableInstr::MakeLocationSummary(Zone* zone,
   const intptr_t kCpuRegistersToPreserve =
       kDartAvailableCpuRegs & ~kNonChangeableInputRegs;
   const intptr_t kFpuRegistersToPreserve =
-      Utils::NBitMask<word>(kNumberOfFpuRegisters) &
+      Utils::SignedNBitMask(kNumberOfFpuRegisters) &
-      ~(Utils::NBitMask<word>(kAbiPreservedFpuRegCount)
+      ~(Utils::SignedNBitMask(kAbiPreservedFpuRegCount)
         << kAbiFirstPreservedFpuReg) &
       ~(1 << FpuTMP);
 

runtime/vm/compiler/backend/il_arm64.cc

@@ -689,7 +689,7 @@ LocationSummary* AssertAssignableInstr::MakeLocationSummary(Zone* zone,
   const intptr_t kCpuRegistersToPreserve =
       kDartAvailableCpuRegs & ~kNonChangeableInputRegs;
   const intptr_t kFpuRegistersToPreserve =
-      Utils::NBitMask<word>(kNumberOfFpuRegisters) & ~Utils::Bit(FpuTMP);
+      Utils::SignedNBitMask(kNumberOfFpuRegisters) & ~(1l << FpuTMP);
 
   const intptr_t kNumTemps = (Utils::CountOneBits64(kCpuRegistersToPreserve) +
                               Utils::CountOneBits64(kFpuRegistersToPreserve));

runtime/vm/datastream.cc

@@ -4,126 +4,11 @@
 
 #include "vm/datastream.h"
 
-#include "platform/text_buffer.h"
 #include "vm/compiler/runtime_api.h"
-#include "vm/os.h"
 #include "vm/zone.h"
 
 namespace dart {
 
-// Setting up needed variables for the unrolled loop sections below.
-#define UNROLLED_INIT()                                                        \
-  using Unsigned = typename std::make_unsigned<T>::type;                       \
-  Unsigned b = ReadByte();                                                     \
-  if ((b & C::kMoreDataMask) == 0) {                                           \
-    if ((b & C::kSignMask) != 0) {                                             \
-      b |= ~Utils::NBitMask<Unsigned>(C::kDataBitsPerByte);                    \
-    }                                                                          \
-    return static_cast<T>(b);                                                  \
-  }                                                                            \
-  T r = static_cast<T>(b & C::kDataByteMask);
-
-// Part of the unrolled loop where the loop may stop, having read the last part,
-// or continue reading.
-#define UNROLLED_BODY(bit_start)                                               \
-  static_assert(bit_start % C::kDataBitsPerByte == 0,                          \
-                "Bit start must be a multiple of the data bits per byte");     \
-  static_assert(bit_start >= 0 && bit_start < kBitsPerByte * sizeof(T),        \
-                "Starting unrolled body at invalid bit position");             \
-  static_assert(bit_start + C::kDataBitsPerByte < kBitsPerByte * sizeof(T),    \
-                "Unrolled body should not contain final bits in value");       \
-  b = ReadByte();                                                              \
-  r |= static_cast<Unsigned>(b & C::kDataByteMask) << bit_start;               \
-  if ((b & C::kMoreDataMask) == 0) {                                           \
-    if ((b & C::kSignMask) != 0) {                                             \
-      r |= ~Utils::NBitMask<T>(bit_start + C::kDataBitsPerByte);               \
-    }                                                                          \
-    return r;                                                                  \
-  }
-
-// The end of the unrolled loop. Does not need to handle sign extension, as the
-// last bits fill the rest of the bitspace.
-#define UNROLLED_END(bit_start)                                                \
-  static_assert(bit_start % C::kDataBitsPerByte == 0,                          \
-                "Bit start must be a multiple of the data bits per byte");     \
-  static_assert(bit_start >= 0 && bit_start < kBitsPerByte * sizeof(T),        \
-                "Starting unrolled end at invalid bit position");              \
-  static_assert(bit_start + C::kDataBitsPerByte >= kBitsPerByte * sizeof(T),   \
-                "Unrolled end does not contain final bits in value");          \
-  b = ReadByte();                                                              \
-  ASSERT_EQUAL((b & C::kMoreDataMask), 0);                                     \
-  r |= static_cast<Unsigned>(b & C::kDataByteMask) << bit_start;               \
-  return r;
-
-uint16_t ReadStream::Read16() {
-  using T = uint16_t;
-  UNROLLED_INIT();
-  UNROLLED_BODY(7);
-  UNROLLED_END(14);
-}
-
-uint32_t ReadStream::Read32() {
-  using T = uint32_t;
-  UNROLLED_INIT();
-  UNROLLED_BODY(7);
-  UNROLLED_BODY(14);
-  UNROLLED_BODY(21);
-  UNROLLED_END(28);
-}
-
-uint64_t ReadStream::Read64() {
-  using T = uint64_t;
-  UNROLLED_INIT();
-  UNROLLED_BODY(7);
-  UNROLLED_BODY(14);
-  UNROLLED_BODY(21);
-  UNROLLED_BODY(28);
-  UNROLLED_BODY(35);
-  UNROLLED_BODY(42);
-  UNROLLED_BODY(49);
-  UNROLLED_BODY(56);
-  UNROLLED_END(63);
-}
-#undef UNROLLED_INIT
-#undef UNROLLED_BODY
-#undef UNROLLED_END
-
-static constexpr intptr_t kRowSize = 16;
-
-void ReadStream::WriteWindow(BaseTextBuffer* buffer,
-                             intptr_t start,
-                             intptr_t window_size) {
-  const intptr_t buffer_size = end_ - buffer_;
-  ASSERT(0 <= start && start <= buffer_size);
-  intptr_t window_start = start - (window_size / 2);
-  intptr_t window_end = start + (window_size / 2);
-  if (window_start < 0) window_start = 0;
-  if (buffer_size < window_start + window_end) window_end = buffer_size;
-  for (intptr_t i = window_start - (window_start % kRowSize); i < window_end;
-       i += kRowSize) {
-    buffer->Printf("%016" Px " ", i);
-    intptr_t j = i;
-    if (j < window_start) {
-      while (j < window_start) {
-        buffer->AddString("    ");
-        ++j;
-      }
-    }
-    for (; j < Utils::Minimum(window_end, i + kRowSize); j++) {
-      buffer->AddChar(j == start ? '|' : ' ');
-      buffer->Printf("%02x", static_cast<uint8_t>(buffer_[j] % kMaxUint8));
-      buffer->AddChar(j == start ? '|' : ' ');
-    }
-    buffer->AddChar('\n');
-  }
-}
-
-void ReadStream::PrintWindow(intptr_t start, intptr_t window_size) {
-  TextBuffer buffer(1024);
-  WriteWindow(&buffer, start, window_size);
-  OS::Print("%s", buffer.buffer());
-}
-
 void BaseWriteStream::WriteTargetWord(word value) {
   ASSERT(compiler::target::kBitsPerWord == kBitsPerWord ||
          Utils::IsAbsoluteUint(compiler::target::kBitsPerWord, value));

runtime/vm/datastream.h

@@ -15,7 +15,14 @@
 
 namespace dart {
 
-class BaseTextBuffer;
+static const int8_t kDataBitsPerByte = 7;
+static const int8_t kByteMask = (1 << kDataBitsPerByte) - 1;
+static const int8_t kMaxUnsignedDataPerByte = kByteMask;
+static const int8_t kMinDataPerByte = -(1 << (kDataBitsPerByte - 1));
+static const int8_t kMaxDataPerByte = (~kMinDataPerByte & kByteMask);  // NOLINT
+static const uint8_t kEndByteMarker = (255 - kMaxDataPerByte);
+static const uint8_t kEndUnsignedByteMarker = (255 - kMaxUnsignedDataPerByte);
+
 struct LEB128Constants : AllStatic {
   // Convenience template for ensuring non-signed types trigger SFINAE.
   template <typename T, typename S>
@@ -28,13 +35,12 @@ struct LEB128Constants : AllStatic {
       typename std::enable_if<std::is_unsigned<T>::value, S>::type;
 
   // (S)LEB128 encodes 7 bits of data per byte (hence 128).
-  static constexpr size_t kDataBitsPerByte = 7;
+  static constexpr uint8_t kDataBitsPerByte = 7;
-  static constexpr auto kDataByteMask =
+  static constexpr uint8_t kDataByteMask = (1 << kDataBitsPerByte) - 1;
-      Utils::NBitMask<uint8_t>(kDataBitsPerByte);
   // If more data follows a given data byte, the high bit is set.
-  static constexpr auto kMoreDataMask = Utils::Bit<uint8_t>(kDataBitsPerByte);
+  static constexpr uint8_t kMoreDataMask = (1 << kDataBitsPerByte);
   // For SLEB128, the high bit in the data of the last byte is the sign bit.
-  static constexpr auto kSignMask = Utils::Bit<uint8_t>(kDataBitsPerByte - 1);
+  static constexpr uint8_t kSignMask = (1 << (kDataBitsPerByte - 1));
 };
 
 class NonStreamingWriteStream;
@@ -87,6 +93,11 @@ class ReadStream : public ValueObject {
     current_ += len;
   }
 
+  template <typename T = intptr_t>
+  T ReadUnsigned() {
+    return Read<T>(kEndUnsignedByteMarker);
+  }
+
   intptr_t Position() const { return current_ - buffer_; }
   void SetPosition(intptr_t value) {
     ASSERT((end_ - buffer_) >= value);
@@ -111,6 +122,11 @@ class ReadStream : public ValueObject {
     return (end_ - current_);
   }
 
+  template <typename T>
+  T Read() {
+    return Read<T>(kEndByteMarker);
+  }
+
   uword ReadWordWith32BitReads() {
     constexpr intptr_t kNumRead32PerWord = kBitsPerWord / kBitsPerInt32;
 
@@ -127,7 +143,7 @@ class ReadStream : public ValueObject {
 
  public:
   template <typename T = uintptr_t>
-  C::only_if_unsigned<T, T> ReadUnsigned() {
+  C::only_if_unsigned<T, T> ReadLEB128() {
     constexpr intptr_t kBitsPerT = kBitsPerByte * sizeof(T);
     T r = 0;
     uint8_t s = 0;
@@ -143,12 +159,12 @@ class ReadStream : public ValueObject {
   }
 
   template <typename T>
-  C::only_if_signed<T, T> ReadUnsigned() {
+  C::only_if_signed<T, T> ReadLEB128() {
-    return bit_cast<T>(ReadUnsigned<typename std::make_unsigned<T>::type>());
+    return bit_cast<T>(ReadLEB128<typename std::make_unsigned<T>::type>());
   }
 
   template <typename T>
-  C::only_if_unsigned<T, T> Read() {
+  C::only_if_unsigned<T, T> ReadSLEB128() {
     constexpr intptr_t kBitsPerT = kBitsPerByte * sizeof(T);
     T r = 0;
     uint8_t s = 0;
@@ -164,33 +180,114 @@ class ReadStream : public ValueObject {
     // value. If the value is negative and the count of data bits is less than
     // the size of the value, then we need to extend the sign by setting the
     // remaining (unset) most significant bits (MSBs).
+    T sign_bits = 0;
     if ((b & C::kSignMask) != 0 && s < kBitsPerT) {
       // Create a bitmask for the current data bits and invert it.
-      r |= ~Utils::NBitMask<T>(s);
+      sign_bits = ~((static_cast<T>(1) << s) - 1);
     }
-    return r;
+    return r | sign_bits;
   }
 
   template <typename T = intptr_t>
-  C::only_if_signed<T, T> Read() {
+  C::only_if_signed<T, T> ReadSLEB128() {
-    return bit_cast<T>(Read<typename std::make_unsigned<T>::type>());
+    return bit_cast<T>(ReadSLEB128<typename std::make_unsigned<T>::type>());
   }
 
  private:
-  uint16_t Read16();
+  uint16_t Read16() { return Read16(kEndByteMarker); }
-  uint32_t Read32();
+
-  uint64_t Read64();
+  uint32_t Read32() { return Read32(kEndByteMarker); }
+
+  uint64_t Read64() { return Read64(kEndByteMarker); }
+
+  template <typename T>
+  T Read(uint8_t end_byte_marker) {
+    using Unsigned = typename std::make_unsigned<T>::type;
+    Unsigned b = ReadByte();
+    if (b > kMaxUnsignedDataPerByte) {
+      return b - end_byte_marker;
+    }
+    T r = 0;
+    uint8_t s = 0;
+    do {
+      r |= static_cast<Unsigned>(b) << s;
+      s += kDataBitsPerByte;
+      b = ReadByte();
+    } while (b <= kMaxUnsignedDataPerByte);
+    return r | (static_cast<Unsigned>(b - end_byte_marker) << s);
+  }
+
+// Setting up needed variables for the unrolled loop sections below.
+#define UNROLLED_INIT()                                                        \
+  using Unsigned = typename std::make_unsigned<T>::type;                       \
+  Unsigned b = ReadByte();                                                     \
+  if (b > kMaxUnsignedDataPerByte) {                                           \
+    return b - end_byte_marker;                                                \
+  }                                                                            \
+  T r = b;
+
+// Part of the unrolled loop where the loop may stop, having read the last part,
+// or continue reading.
+#define UNROLLED_BODY(bit_start)                                               \
+  static_assert(bit_start % kDataBitsPerByte == 0,                             \
+                "Bit start must be a multiple of the data bits per byte");     \
+  static_assert(bit_start >= 0 && bit_start < kBitsPerByte * sizeof(T),        \
+                "Starting unrolled body at invalid bit position");             \
+  static_assert(bit_start + kDataBitsPerByte < kBitsPerByte * sizeof(T),       \
+                "Unrolled body should not contain final bits in value");       \
+  b = ReadByte();                                                              \
+  if (b > kMaxUnsignedDataPerByte) {                                           \
+    return r | (static_cast<T>(b - end_byte_marker) << bit_start);             \
+  }                                                                            \
+  r |= b << bit_start;
+
+// The end of the unrolled loop.
+#define UNROLLED_END(bit_start)                                                \
+  static_assert(bit_start % kDataBitsPerByte == 0,                             \
+                "Bit start must be a multiple of the data bits per byte");     \
+  static_assert(bit_start >= 0 && bit_start < kBitsPerByte * sizeof(T),        \
+                "Starting unrolled end at invalid bit position");              \
+  static_assert(bit_start + kDataBitsPerByte >= kBitsPerByte * sizeof(T),      \
+                "Unrolled end does not contain final bits in value");          \
+  b = ReadByte();                                                              \
+  ASSERT(b > kMaxUnsignedDataPerByte);                                         \
+  return r | (static_cast<T>(b - end_byte_marker) << bit_start);
+
+  uint16_t Read16(uint8_t end_byte_marker) {
+    using T = uint16_t;
+    UNROLLED_INIT();
+    UNROLLED_BODY(7);
+    UNROLLED_END(14);
+  }
+
+  uint32_t Read32(uint8_t end_byte_marker) {
+    using T = uint32_t;
+    UNROLLED_INIT();
+    UNROLLED_BODY(7);
+    UNROLLED_BODY(14);
+    UNROLLED_BODY(21);
+    UNROLLED_END(28);
+  }
+
+  uint64_t Read64(uint8_t end_byte_marker) {
+    using T = uint64_t;
+    UNROLLED_INIT();
+    UNROLLED_BODY(7);
+    UNROLLED_BODY(14);
+    UNROLLED_BODY(21);
+    UNROLLED_BODY(28);
+    UNROLLED_BODY(35);
+    UNROLLED_BODY(42);
+    UNROLLED_BODY(49);
+    UNROLLED_BODY(56);
+    UNROLLED_END(63);
+  }
 
   DART_FORCE_INLINE uint8_t ReadByte() {
     ASSERT(current_ < end_);
     return *current_++;
   }
 
-  void WriteWindow(BaseTextBuffer* buffer,
-                   intptr_t start,
-                   intptr_t window_size = 64);
-  void PrintWindow(intptr_t start, intptr_t window_size = 64);
-
  private:
   const uint8_t* buffer_;
   const uint8_t* current_;
@@ -267,6 +364,16 @@ class BaseWriteStream : public ValueObject {
     }
   }
 
+  template <typename T>
+  void WriteUnsigned(T value) {
+    ASSERT(value >= 0);
+    while (value > kMaxUnsignedDataPerByte) {
+      WriteByte(static_cast<uint8_t>(value & kByteMask));
+      value = value >> kDataBitsPerByte;
+    }
+    WriteByte(static_cast<uint8_t>(value + kEndUnsignedByteMarker));
+  }
+
   void WriteBytes(const void* addr, intptr_t len) {
     if (len != 0) {
       EnsureSpace(len);
@@ -305,6 +412,16 @@ class BaseWriteStream : public ValueObject {
     current_ += len;  // Not len + 1 to swallow the terminating NUL.
   }
 
+  template <typename T>
+  void Write(T value) {
+    T v = value;
+    while (v < kMinDataPerByte || v > kMaxDataPerByte) {
+      WriteByte(static_cast<uint8_t>(v & kByteMask));
+      v = v >> kDataBitsPerByte;
+    }
+    WriteByte(static_cast<uint8_t>(v + kEndByteMarker));
+  }
+
   template <typename T>
   void WriteFixed(T value) {
     WriteBytes(&value, sizeof(value));
@@ -322,7 +439,7 @@ class BaseWriteStream : public ValueObject {
 
  public:
   template <typename T>
-  C::only_if_unsigned<T, void> WriteUnsigned(T value) {
+  C::only_if_unsigned<T, void> WriteLEB128(T value) {
     T remainder = value;
     bool is_last_part;
     do {
@@ -339,15 +456,15 @@ class BaseWriteStream : public ValueObject {
   }
 
   template <typename T>
-  C::only_if_signed<T, void> WriteUnsigned(T value) {
+  C::only_if_signed<T, void> WriteLEB128(T value) {
     // If we're trying to LEB128 encode a negative value, chances are we should
     // be using SLEB128 instead.
     ASSERT(value >= 0);
-    return WriteUnsigned(bit_cast<typename std::make_unsigned<T>::type>(value));
+    return WriteLEB128(bit_cast<typename std::make_unsigned<T>::type>(value));
   }
 
   template <typename T>
-  C::only_if_signed<T, void> Write(T value) {
+  C::only_if_signed<T, void> WriteSLEB128(T value) {
     constexpr intptr_t kBitsPerT = kBitsPerByte * sizeof(T);
     using Unsigned = typename std::make_unsigned<T>::type;
     // Record whether the original value was negative.
@@ -392,8 +509,8 @@ class BaseWriteStream : public ValueObject {
   }
 
   template <typename T>
-  C::only_if_unsigned<T, void> Write(T value) {
+  C::only_if_unsigned<T, void> WriteSLEB128(T value) {
-    return Write(bit_cast<typename std::make_signed<T>::type>(value));
+    return WriteSLEB128(bit_cast<typename std::make_signed<T>::type>(value));
   }
 
  protected:

runtime/vm/datastream_test.cc

@@ -126,4 +126,60 @@ TEST_CASE(ReadStream_Read64) {
   TestRaw<int64_t>();
 }
 
+TEST_CASE(BaseWriteStream_WriteLEB128) {
+  MallocWriteStream writer(1 * KB);
+  for (uintptr_t i = 0; i < kUnsignedEnd; i++) {
+    writer.WriteLEB128(i);
+  }
+  DEFINE_LARGE_CONSTANTS(uintptr_t);
+  writer.WriteLEB128(all_ones);
+  writer.WriteLEB128(min);
+  writer.WriteLEB128(max);
+  writer.WriteLEB128(half_min);
+  writer.WriteLEB128(half_max);
+  ReadStream reader(writer.buffer(), writer.bytes_written());
+  for (uintptr_t i = 0; i < kUnsignedEnd; i++) {
+    const uintptr_t r = reader.ReadLEB128();
+    EXPECT_EQ(i, r);
+  }
+  const uintptr_t read_all_ones = reader.ReadLEB128();
+  EXPECT_EQ(all_ones, read_all_ones);
+  const uintptr_t read_min = reader.ReadLEB128();
+  EXPECT_EQ(min, read_min);
+  const uintptr_t read_max = reader.ReadLEB128();
+  EXPECT_EQ(max, read_max);
+  const uintptr_t read_half_min = reader.ReadLEB128();
+  EXPECT_EQ(half_min, read_half_min);
+  const uintptr_t read_half_max = reader.ReadLEB128();
+  EXPECT_EQ(half_max, read_half_max);
+}
+
+TEST_CASE(BaseWriteStream_WriteSLEB128) {
+  MallocWriteStream writer(1 * KB);
+  for (intptr_t i = kSignedStart; i < kSignedEnd; i++) {
+    writer.WriteSLEB128(i);
+  }
+  DEFINE_LARGE_CONSTANTS(intptr_t);
+  writer.WriteSLEB128(all_ones);
+  writer.WriteSLEB128(min);
+  writer.WriteSLEB128(max);
+  writer.WriteSLEB128(half_min);
+  writer.WriteSLEB128(half_max);
+  ReadStream reader(writer.buffer(), writer.bytes_written());
+  for (intptr_t i = kSignedStart; i < kSignedEnd; i++) {
+    const intptr_t r = reader.ReadSLEB128();
+    EXPECT_EQ(i, r);
+  }
+  const intptr_t read_all_ones = reader.ReadSLEB128();
+  EXPECT_EQ(all_ones, read_all_ones);
+  const intptr_t read_min = reader.ReadSLEB128();
+  EXPECT_EQ(min, read_min);
+  const intptr_t read_max = reader.ReadSLEB128();
+  EXPECT_EQ(max, read_max);
+  const intptr_t read_half_min = reader.ReadSLEB128();
+  EXPECT_EQ(half_min, read_half_min);
+  const intptr_t read_half_max = reader.ReadSLEB128();
+  EXPECT_EQ(half_max, read_half_max);
+}
+
 }  // namespace dart

runtime/vm/elf.cc

@@ -1106,8 +1106,8 @@ class DwarfElfStream : public DwarfWriteStream {
         stream_(ASSERT_NOTNULL(stream)),
         table_(table) {}
 
-  void sleb128(intptr_t value) { stream_->Write(value); }
+  void sleb128(intptr_t value) { stream_->WriteSLEB128(value); }
-  void uleb128(uintptr_t value) { stream_->WriteUnsigned(value); }
+  void uleb128(uintptr_t value) { stream_->WriteLEB128(value); }
   void u1(uint8_t value) { stream_->WriteByte(value); }
   void u2(uint16_t value) { stream_->WriteFixed(value); }
   void u4(uint32_t value) { stream_->WriteFixed(value); }

runtime/vm/kernel_binary.h

@@ -309,14 +309,14 @@ class Reader : public ValueObject {
 
   intptr_t ReadSLEB128() {
     ReadStream stream(this->buffer(), size_, offset_);
-    const intptr_t result = stream.Read();
+    const intptr_t result = stream.ReadSLEB128();
     offset_ = stream.Position();
     return result;
   }
 
   int64_t ReadSLEB128AsInt64() {
     ReadStream stream(this->buffer(), size_, offset_);
-    const int64_t result = stream.Read<int64_t>();
+    const int64_t result = stream.ReadSLEB128<int64_t>();
     offset_ = stream.Position();
     return result;
   }

runtime/vm/object.cc

@@ -14667,7 +14667,7 @@ bool CompressedStackMaps::Iterator::MoveNext() {
   NoSafepointScope scope;
   ReadStream stream(maps_.untag()->data(), maps_.payload_size(), next_offset_);
 
-  auto const pc_delta = stream.ReadUnsigned();
+  auto const pc_delta = stream.ReadLEB128();
   ASSERT(pc_delta <= (kMaxUint32 - current_pc_offset_));
   current_pc_offset_ += pc_delta;
 
@@ -14675,7 +14675,7 @@ bool CompressedStackMaps::Iterator::MoveNext() {
   // the post-delta part of inlined entries has the same information as
   // global table entries.
   if (maps_.UsesGlobalTable()) {
-    current_global_table_offset_ = stream.ReadUnsigned();
+    current_global_table_offset_ = stream.ReadLEB128();
     ASSERT(current_global_table_offset_ < bits_container_.payload_size());
 
     // Since generally we only use entries in the GC and the GC only needs
@@ -14688,10 +14688,10 @@ bool CompressedStackMaps::Iterator::MoveNext() {
 
     next_offset_ = stream.Position();
   } else {
-    current_spill_slot_bit_count_ = stream.ReadUnsigned();
+    current_spill_slot_bit_count_ = stream.ReadLEB128();
     ASSERT(current_spill_slot_bit_count_ >= 0);
 
-    current_non_spill_slot_bit_count_ = stream.ReadUnsigned();
+    current_non_spill_slot_bit_count_ = stream.ReadLEB128();
     ASSERT(current_non_spill_slot_bit_count_ >= 0);
 
     const auto stackmap_bits =
@@ -14737,10 +14737,10 @@ void CompressedStackMaps::Iterator::LazyLoadGlobalTableEntry() const {
                     bits_container_.payload_size(),
                     current_global_table_offset_);
 
-  current_spill_slot_bit_count_ = stream.ReadUnsigned();
+  current_spill_slot_bit_count_ = stream.ReadLEB128();
   ASSERT(current_spill_slot_bit_count_ >= 0);
 
-  current_non_spill_slot_bit_count_ = stream.ReadUnsigned();
+  current_non_spill_slot_bit_count_ = stream.ReadLEB128();
   ASSERT(current_non_spill_slot_bit_count_ >= 0);
 
   const auto stackmap_bits = Length();

runtime/vm/object.h

@@ -5641,7 +5641,7 @@ class PcDescriptors : public Object {
                         byte_index_);
       // Moves to record that matches kind_mask_.
       while (byte_index_ < descriptors_.Length()) {
-        const int32_t kind_and_metadata = stream.Read<int32_t>();
+        const int32_t kind_and_metadata = stream.ReadSLEB128<int32_t>();
         cur_kind_ = UntaggedPcDescriptors::KindAndMetadata::DecodeKind(
             kind_and_metadata);
         cur_try_index_ = UntaggedPcDescriptors::KindAndMetadata::DecodeTryIndex(
@@ -5650,12 +5650,12 @@ class PcDescriptors : public Object {
             UntaggedPcDescriptors::KindAndMetadata::DecodeYieldIndex(
                 kind_and_metadata);
 
-        cur_pc_offset_ += stream.Read();
+        cur_pc_offset_ += stream.ReadSLEB128();
 
         if (!FLAG_precompiled_mode) {
-          cur_deopt_id_ += stream.Read();
+          cur_deopt_id_ += stream.ReadSLEB128();
-          cur_token_pos_ =
+          cur_token_pos_ = Utils::AddWithWrapAround(
-              Utils::AddWithWrapAround(cur_token_pos_, stream.Read<int32_t>());
+              cur_token_pos_, stream.ReadSLEB128<int32_t>());
         }
         byte_index_ = stream.Position();
 

runtime/vm/program_visitor.cc

@@ -502,8 +502,8 @@ class StackMapEntry : public ZoneAllocated {
   // initial offset of the entry in the array.
   intptr_t EncodeTo(NonStreamingWriteStream* stream) {
     auto const current_offset = stream->Position();
-    stream->WriteUnsigned(spill_slot_bit_count_);
+    stream->WriteLEB128(spill_slot_bit_count_);
-    stream->WriteUnsigned(non_spill_slot_bit_count_);
+    stream->WriteLEB128(non_spill_slot_bit_count_);
     {
       NoSafepointScope scope;
       stream->WriteBytes(PayloadData(), PayloadLength());
@@ -711,8 +711,8 @@ void ProgramVisitor::NormalizeAndDedupCompressedStackMaps(
         StackMapEntry entry(zone_, it);
         const intptr_t entry_offset = entry_offsets_.LookupValue(&entry);
         const intptr_t pc_delta = it.pc_offset() - last_offset;
-        new_payload.WriteUnsigned(pc_delta);
+        new_payload.WriteLEB128(pc_delta);
-        new_payload.WriteUnsigned(entry_offset);
+        new_payload.WriteLEB128(entry_offset);
         last_offset = it.pc_offset();
       }
       return CompressedStackMaps::NewUsingTable(new_payload.buffer(),

runtime/vm/v8_snapshot_writer.h

@@ -58,7 +58,7 @@ class V8SnapshotProfileWriter : public ZoneAllocated {
    private:
     static constexpr size_t kIdSpaceBits =
         Utils::BitLength(static_cast<int64_t>(IdSpace::kArtificial));
-    static constexpr int64_t kIdSpaceMask = Utils::NBitMask(kIdSpaceBits);
+    static constexpr int64_t kIdSpaceMask = Utils::NBitMaskUnsafe(kIdSpaceBits);
     static const char* IdSpaceToCString(IdSpace space);
 
     int64_t encoded_;