Merge pull request #73624 from tbkka/tbkka-mpe-sparebits-6.0

[6.0] Compute spare bit mask from first principles

Author: tbkka

include/swift/RemoteInspection/BitMask.h

@@ -0,0 +1,339 @@
+//===--- Bitmask.h - Swift Bitmask type for Reflection ----*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// Used by TypeLowering logic to compute masks for in-memory representations
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_REFLECTION_BITMASK_H
+#define SWIFT_REFLECTION_BITMASK_H
+
+#include "swift/Remote/MemoryReader.h"
+#include <sstream>
+
+namespace swift {
+namespace reflection {
+
+// A variable-length bitmap used to track "spare bits" for general multi-payload
+// enums.  Note:  These are not arbitrary-sized!  They are always a multiple
+// of 8 bits in size, and always aligned on an 8-bit boundary.
+class BitMask {
+  static constexpr unsigned maxSize = 128 * 1024 * 1024; // 128MB
+
+  unsigned size; // Size of mask _in bytes_
+  uint8_t *mask;
+public:
+  ~BitMask() {
+    free(mask);
+  }
+private:
+  // Construct a bitmask of the appropriate number of bytes
+  // initialized to all bits set
+  BitMask(unsigned sizeInBytes = 0): size(sizeInBytes) {
+    assert(size < maxSize && "Trying to build a too-large bitmask");
+    if (size > maxSize || size == 0) {
+      size = 0;
+      mask = nullptr;
+      return;
+    }
+
+    mask = (uint8_t *)malloc(size);
+
+    if (!mask) {
+      // Malloc might fail if size is large due to some bad data. Assert in
+      // asserts builds, and fail gracefully in non-asserts builds by
+      // constructing an empty BitMask.
+      assert(false && "Failed to allocate BitMask");
+      size = 0;
+      return;
+    }
+
+    memset(mask, 0xff, size);
+  }
+
+public:
+  static BitMask zeroMask(unsigned sizeInBytes) {
+    auto mask = BitMask(sizeInBytes);
+    mask.makeZero();
+    return mask;
+  }
+
+  static BitMask oneMask(unsigned sizeInBytes) {
+    auto mask = BitMask(sizeInBytes);
+    return mask;
+  }
+
+  BitMask(unsigned sizeInBytes, uint64_t sourceMask): size(sizeInBytes) {
+    mask = (uint8_t *)calloc(1, sizeInBytes);
+    memcpy(mask, &sourceMask, sizeInBytes);
+  }
+
+  // Construct a bitmask of the appropriate number of bytes
+  // initialized with bits from the specified buffer
+  BitMask(unsigned sizeInBytes, const uint8_t *initialValue,
+          unsigned initialValueBytes, unsigned offset)
+      : size(sizeInBytes) {
+    // Gracefully fail by constructing an empty mask if we exceed the size
+    // limit.
+    if (size > maxSize) {
+      size = 0;
+      mask = nullptr;
+      return;
+    }
+
+    // Bad data could cause the initial value location to be off the end of our
+    // size. If initialValueBytes + offset is beyond sizeInBytes (or overflows),
+    // assert in asserts builds, and fail gracefully in non-asserts builds by
+    // constructing an empty BitMask.
+    bool overflowed = false;
+    unsigned initialValueEnd =
+        llvm::SaturatingAdd(initialValueBytes, offset, &overflowed);
+    if (overflowed) {
+      assert(false && "initialValueBytes + offset overflowed");
+      size = 0;
+      mask = nullptr;
+      return;
+    }
+    assert(initialValueEnd <= sizeInBytes);
+    if (initialValueEnd > size) {
+      assert(false && "initialValueBytes + offset is greater than size");
+      size = 0;
+      mask = nullptr;
+      return;
+    }
+
+    mask = (uint8_t *)calloc(1, size);
+
+    if (!mask) {
+      // Malloc might fail if size is large due to some bad data. Assert in
+      // asserts builds, and fail gracefully in non-asserts builds by
+      // constructing an empty BitMask.
+      assert(false && "Failed to allocate BitMask");
+      size = 0;
+      return;
+    }
+
+    memcpy(mask + offset, initialValue, initialValueBytes);
+  }
+  // Move constructor moves ownership and zeros the src
+  BitMask(BitMask&& src) noexcept: size(src.size), mask(std::move(src.mask)) {
+    src.size = 0;
+    src.mask = nullptr;
+  }
+  // Copy constructor makes a copy of the mask storage
+  BitMask(const BitMask& src) noexcept: size(src.size), mask(nullptr) {
+    mask = (uint8_t *)malloc(size);
+    memcpy(mask, src.mask, size);
+  }
+
+  std::string str() const {
+    std::ostringstream buff;
+    buff << size << ":0x";
+    for (unsigned i = 0; i < size; i++) {
+      buff << std::hex << ((mask[i] >> 4) & 0x0f) << (mask[i] & 0x0f);
+    }
+    return buff.str();
+  }
+
+  bool operator==(const BitMask& rhs) const {
+    // The two masks may be of different sizes.
+    // The common prefix must be identical.
+    size_t common = std::min(size, rhs.size);
+    if (memcmp(mask, rhs.mask, common) != 0)
+      return false;
+    // The remainder of the longer mask must be
+    // all zero bits.
+    unsigned mustBeZeroSize = std::max(size, rhs.size) - common;
+    uint8_t *mustBeZero;
+    if (size < rhs.size) {
+      mustBeZero = rhs.mask + size;
+    } else if (size > rhs.size) {
+      mustBeZero = mask + rhs.size;
+    }
+    for (unsigned i = 0; i < mustBeZeroSize; ++i) {
+      if (mustBeZero[i] != 0) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  bool operator!=(const BitMask& rhs) const {
+    return !(*this == rhs);
+  }
+
+  bool isNonZero() const { return !isZero(); }
+
+  bool isZero() const {
+    for (unsigned i = 0; i < size; ++i) {
+      if (mask[i] != 0) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  void makeZero() {
+    memset(mask, 0, size * sizeof(mask[0]));
+  }
+
+  void complement() {
+    for (unsigned i = 0; i < size; ++i) {
+      mask[i] = ~mask[i];
+    }
+  }
+
+  int countSetBits() const {
+    static const int counter[] =
+      {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};
+    int bits = 0;
+    for (unsigned i = 0; i < size; ++i) {
+      bits += counter[mask[i] >> 4] + counter[mask[i] & 15];
+    }
+    return bits;
+  }
+
+  int countZeroBits() const {
+    return (size * 8) - countSetBits();
+  }
+
+  // Treat the provided value as a mask, `and` it with
+  // the part of the mask at the provided byte offset.
+  // Bits outside the specified area are unchanged.
+  template<typename IntegerType>
+  void andMask(IntegerType value, unsigned byteOffset) {
+    andMask((void *)&value, sizeof(value), byteOffset);
+  }
+
+  // As above, but using the provided bitmask instead
+  // of an integer.
+  void andMask(BitMask mask, unsigned offset) {
+    andMask(mask.mask, mask.size, offset);
+  }
+
+  // As above, but using the complement of the
+  // provided mask.
+  void andNotMask(BitMask mask, unsigned offset) {
+    if (offset < size) {
+      andNotMask(mask.mask, mask.size, offset);
+    }
+  }
+
+  // Zero all bits except for the `n` most significant ones.
+  void keepOnlyMostSignificantBits(unsigned n) {
+    if (size < 1) {
+      return;
+    }
+#if defined(__BIG_ENDIAN__)
+    assert(false && "Big endian not supported for readMaskedInteger");
+#else
+    unsigned count = 0;
+    unsigned i = size;
+    while (i > 0) {
+      i -= 1;
+      if (count < n) {
+        for (int b = 128; b > 0; b >>= 1) {
+          if (count >= n) {
+            mask[i] &= ~b;
+          } else if ((mask[i] & b) != 0) {
+            ++count;
+          }
+        }
+      } else {
+        mask[i] = 0;
+      }
+    }
+#endif
+  }
+
+  void keepOnlyLeastSignificantBytes(unsigned n) {
+    if (size > n) {
+      size = n;
+    }
+  }
+
+  unsigned numBits() const {
+    return size * 8;
+  }
+
+  unsigned numSetBits() const {
+    unsigned count = 0;
+    for (unsigned i = 0; i < size; ++i) {
+      if (mask[i] != 0) {
+        for (unsigned b = 1; b < 256; b <<= 1) {
+          if ((mask[i] & b) != 0) {
+            ++count;
+          }
+        }
+      }
+    }
+    return count;
+  }
+
+  // Read a mask-sized area from the target and collect
+  // the masked bits into a single integer.
+  template<typename IntegerType>
+   bool readMaskedInteger(remote::MemoryReader &reader,
+                         remote::RemoteAddress address,
+                         IntegerType *dest) const {
+    auto data = reader.readBytes(address, size);
+    if (!data) {
+      return false;
+    }
+#if defined(__BIG_ENDIAN__)
+    assert(false && "Big endian not supported for readMaskedInteger");
+#else
+    IntegerType result = 0;
+    IntegerType resultBit = 1; // Start from least-significant bit
+    auto bytes = static_cast<const uint8_t *>(data.get());
+    for (unsigned i = 0; i < size; ++i) {
+      for (unsigned b = 1; b < 256; b <<= 1) {
+        if ((mask[i] & b) != 0) {
+          if ((bytes[i] & b) != 0) {
+            result |= resultBit;
+          }
+          resultBit <<= 1;
+        }
+      }
+    }
+    *dest = result;
+    return true;
+#endif
+  }
+
+private:
+  void andMask(void *maskData, unsigned len, unsigned offset) {
+    if (offset < size) {
+      unsigned common = std::min(len, size - offset);
+      uint8_t *maskBytes = (uint8_t *)maskData;
+      for (unsigned i = 0; i < common; ++i) {
+        mask[i + offset] &= maskBytes[i];
+      }
+    }
+  }
+
+  void andNotMask(void *maskData, unsigned len, unsigned offset) {
+    assert(offset < size);
+    if (offset < size) {
+      unsigned common = std::min(len, size - offset);
+      uint8_t *maskBytes = (uint8_t *)maskData;
+      for (unsigned i = 0; i < common; ++i) {
+        mask[i + offset] &= ~maskBytes[i];
+      }
+    }
+  }
+};
+
+} // namespace reflection
+} // namespace swift
+
+#endif

include/swift/RemoteInspection/TypeLowering.h

@@ -23,6 +23,7 @@
 #include "llvm/Support/Casting.h"
 #include "swift/Remote/MetadataReader.h"
 #include "swift/Remote/TypeInfoProvider.h"
+#include "swift/RemoteInspection/BitMask.h"
 #include "swift/RemoteInspection/DescriptorFinder.h"
 
 #include <memory>
@@ -34,6 +35,7 @@ using llvm::cast;
 using llvm::dyn_cast;
 using remote::RemoteRef;
 
+class TypeConverter;
 class TypeRef;
 class TypeRefBuilder;
 class BuiltinTypeDescriptor;
@@ -158,6 +160,11 @@ class TypeInfo {
     return false;
   }
 
+  // Calculate and return the spare bit mask for this type
+  virtual BitMask getSpareBits(TypeConverter &TC, bool &hasAddrOnly) const {
+    return BitMask::zeroMask(getSize());
+  }
+
   virtual ~TypeInfo() { }
 };
 
@@ -195,6 +202,8 @@ class BuiltinTypeInfo : public TypeInfo {
                                 remote::RemoteAddress address,
                                 int *extraInhabitantIndex) const override;
 
+  BitMask getSpareBits(TypeConverter &TC, bool &hasAddrOnly) const override;
+
   static bool classof(const TypeInfo *TI) {
     return TI->getKind() == TypeInfoKind::Builtin;
   }
@@ -222,6 +231,8 @@ class RecordTypeInfo : public TypeInfo {
                                 remote::RemoteAddress address,
                                 int *index) const override;
 
+  BitMask getSpareBits(TypeConverter &TC, bool &hasAddrOnly) const override;
+
   static bool classof(const TypeInfo *TI) {
     return TI->getKind() == TypeInfoKind::Record;
   }
@@ -330,6 +341,8 @@ class ReferenceTypeInfo : public TypeInfo {
     return reader.readHeapObjectExtraInhabitantIndex(address, extraInhabitantIndex);
   }
 
+  BitMask getSpareBits(TypeConverter &TC, bool &hasAddrOnly) const override;
+
   static bool classof(const TypeInfo *TI) {
     return TI->getKind() == TypeInfoKind::Reference;
   }