Revert "[MemProf] Change histogram storage from uint64_t to uint16_t" (#151382)

Reverts llvm/llvm-project#147854

Test failure when building with gcc.
https://lab.llvm.org/buildbot/#/builders/174/builds/21989

Author: Snehasish Kumar

compiler-rt/include/profile/MemProfData.inc

@@ -33,10 +33,11 @@
    (uint64_t)'o' << 24 | (uint64_t)'f' << 16 | (uint64_t)'r' << 8 | (uint64_t)129)
 
 // The version number of the raw binary format.
-#define MEMPROF_RAW_VERSION 5ULL
+#define MEMPROF_RAW_VERSION 4ULL
 
 // Currently supported versions.
-#define MEMPROF_RAW_SUPPORTED_VERSIONS {3ULL, 4ULL, 5ULL}
+#define MEMPROF_RAW_SUPPORTED_VERSIONS                                         \
+  { 3ULL, 4ULL }
 
 #define MEMPROF_V3_MIB_SIZE 132ULL;
 
@@ -228,41 +229,6 @@ void Merge(const MemInfoBlock &newMIB) {
 } __attribute__((__packed__));
 #endif
 
-constexpr int MantissaBits = 12;
-constexpr int ExponentBits = 4;
-constexpr uint16_t MaxMantissa = (1U << MantissaBits) - 1;
-constexpr uint16_t MaxExponent = (1U << ExponentBits) - 1;
-constexpr uint64_t MaxRepresentableValue = static_cast<uint64_t>(MaxMantissa)
-                                           << MaxExponent;
-
-// Encodes a 64-bit unsigned integer into a 16-bit scaled integer format.
-inline uint16_t encodeHistogramCount(uint64_t Count) {
-  if (Count == 0)
-    return 0;
-
-  if (Count > MaxRepresentableValue)
-    Count = MaxRepresentableValue;
-
-  if (Count <= MaxMantissa)
-    return Count;
-
-  uint64_t M = Count;
-  uint16_t E = 0;
-  while (M > MaxMantissa) {
-    M = (M + 1) >> 1;
-    E++;
-  }
-  return (E << MantissaBits) | static_cast<uint16_t>(M);
-}
-
-// Decodes a 16-bit scaled integer and returns the
-// decoded 64-bit unsigned integer.
-inline uint64_t decodeHistogramCount(uint16_t EncodedValue) {
-  const uint16_t E = EncodedValue >> MantissaBits;
-  const uint16_t M = EncodedValue & MaxMantissa;
-  return static_cast<uint64_t>(M) << E;
-}
-
 } // namespace memprof
 } // namespace llvm
 

compiler-rt/lib/memprof/memprof_rawprofile.cpp

@@ -19,7 +19,6 @@ using ::__sanitizer::Vector;
 using ::llvm::memprof::MemInfoBlock;
 using SegmentEntry = ::llvm::memprof::SegmentEntry;
 using Header = ::llvm::memprof::Header;
-using ::llvm::memprof::encodeHistogramCount;
 
 namespace {
 template <class T> char *WriteBytes(const T &Pod, char *Buffer) {
@@ -170,15 +169,13 @@ void SerializeMIBInfoToBuffer(MIBMapTy &MIBMap, const Vector<u64> &StackIds,
     // FIXME: We unnecessarily serialize the AccessHistogram pointer. Adding a
     // serialization schema will fix this issue. See also FIXME in
     // deserialization.
-    auto &MIB = (*h)->mib;
-    Ptr = WriteBytes(MIB, Ptr);
-    for (u64 j = 0; j < MIB.AccessHistogramSize; ++j) {
-      u16 HistogramEntry =
-          encodeHistogramCount(((u64 *)(MIB.AccessHistogram))[j]);
+    Ptr = WriteBytes((*h)->mib, Ptr);
+    for (u64 j = 0; j < (*h)->mib.AccessHistogramSize; ++j) {
+      u64 HistogramEntry = ((u64 *)((*h)->mib.AccessHistogram))[j];
       Ptr = WriteBytes(HistogramEntry, Ptr);
     }
-    if (MIB.AccessHistogramSize > 0) {
-      InternalFree((void *)MIB.AccessHistogram);
+    if ((*h)->mib.AccessHistogramSize > 0) {
+      InternalFree((void *)((*h)->mib.AccessHistogram));
     }
   }
   CHECK(ExpectedNumBytes >= static_cast<u64>(Ptr - Buffer) &&
@@ -252,7 +249,7 @@ u64 SerializeToRawProfile(MIBMapTy &MIBMap, ArrayRef<LoadedModule> Modules,
       },
       reinterpret_cast<void *>(&TotalAccessHistogramEntries));
   const u64 NumHistogramBytes =
-      RoundUpTo(TotalAccessHistogramEntries * sizeof(uint16_t), 8);
+      RoundUpTo(TotalAccessHistogramEntries * sizeof(uint64_t), 8);
 
   const u64 NumStackBytes = RoundUpTo(StackSizeBytes(StackIds), 8);
 

compiler-rt/lib/memprof/tests/CMakeLists.txt

@@ -26,7 +26,6 @@ set(MEMPROF_SOURCES
   ../memprof_rawprofile.cpp)
 
 set(MEMPROF_UNITTESTS
-  histogram_encoding.cpp
   rawprofile.cpp
   driver.cpp)
 

compiler-rt/lib/memprof/tests/histogram_encoding.cpp

@@ -33,10 +33,11 @@
    (uint64_t)'o' << 24 | (uint64_t)'f' << 16 | (uint64_t)'r' << 8 | (uint64_t)129)
 
 // The version number of the raw binary format.
-#define MEMPROF_RAW_VERSION 5ULL
+#define MEMPROF_RAW_VERSION 4ULL
 
 // Currently supported versions.
-#define MEMPROF_RAW_SUPPORTED_VERSIONS {3ULL, 4ULL, 5ULL}
+#define MEMPROF_RAW_SUPPORTED_VERSIONS                                         \
+  { 3ULL, 4ULL }
 
 #define MEMPROF_V3_MIB_SIZE 132ULL;
 
@@ -228,41 +229,6 @@ void Merge(const MemInfoBlock &newMIB) {
 } __attribute__((__packed__));
 #endif
 
-constexpr int MantissaBits = 12;
-constexpr int ExponentBits = 4;
-constexpr uint16_t MaxMantissa = (1U << MantissaBits) - 1;
-constexpr uint16_t MaxExponent = (1U << ExponentBits) - 1;
-constexpr uint64_t MaxRepresentableValue = static_cast<uint64_t>(MaxMantissa)
-                                           << MaxExponent;
-
-// Encodes a 64-bit unsigned integer into a 16-bit scaled integer format.
-inline uint16_t encodeHistogramCount(uint64_t Count) {
-  if (Count == 0)
-    return 0;
-
-  if (Count > MaxRepresentableValue)
-    Count = MaxRepresentableValue;
-
-  if (Count <= MaxMantissa)
-    return Count;
-
-  uint64_t M = Count;
-  uint16_t E = 0;
-  while (M > MaxMantissa) {
-    M = (M + 1) >> 1;
-    E++;
-  }
-  return (E << MantissaBits) | static_cast<uint16_t>(M);
-}
-
-// Decodes a 16-bit scaled integer and returns the
-// decoded 64-bit unsigned integer.
-inline uint64_t decodeHistogramCount(uint16_t EncodedValue) {
-  const uint16_t E = EncodedValue >> MantissaBits;
-  const uint16_t M = EncodedValue & MaxMantissa;
-  return static_cast<uint64_t>(M) << E;
-}
-
 } // namespace memprof
 } // namespace llvm
 

compiler-rt/test/memprof/TestCases/memprof_histogram_uint8.cpp

@@ -135,7 +135,7 @@ readMemInfoBlocksV3(const char *Ptr) {
 }
 
 llvm::SmallVector<std::pair<uint64_t, MemInfoBlock>>
-readMemInfoBlocksCommon(const char *Ptr, bool IsHistogramEncoded = false) {
+readMemInfoBlocksV4(const char *Ptr) {
   using namespace support;
 
   const uint64_t NumItemsToRead =
@@ -145,43 +145,27 @@ readMemInfoBlocksCommon(const char *Ptr, bool IsHistogramEncoded = false) {
   for (uint64_t I = 0; I < NumItemsToRead; I++) {
     const uint64_t Id =
         endian::readNext<uint64_t, llvm::endianness::little, unaligned>(Ptr);
-
+    // We cheat a bit here and remove the const from cast to set the
+    // Histogram Pointer to newly allocated buffer.
     MemInfoBlock MIB = *reinterpret_cast<const MemInfoBlock *>(Ptr);
+
+    // Only increment by size of MIB since readNext implicitly increments.
     Ptr += sizeof(MemInfoBlock);
 
     if (MIB.AccessHistogramSize > 0) {
-      // The in-memory representation uses uint64_t for histogram entries.
       MIB.AccessHistogram =
           (uintptr_t)malloc(MIB.AccessHistogramSize * sizeof(uint64_t));
-      for (uint64_t J = 0; J < MIB.AccessHistogramSize; J++) {
-        if (!IsHistogramEncoded) {
-          ((uint64_t *)MIB.AccessHistogram)[J] =
-              endian::readNext<uint64_t, llvm::endianness::little, unaligned>(
-                  Ptr);
-        } else {
-          // The encoded on-disk format (V5 onwards) uses uint16_t.
-          const uint16_t Val =
-              endian::readNext<uint16_t, llvm::endianness::little, unaligned>(
-                  Ptr);
-          ((uint64_t *)MIB.AccessHistogram)[J] = decodeHistogramCount(Val);
-        }
-      }
+    }
+
+    for (uint64_t J = 0; J < MIB.AccessHistogramSize; J++) {
+      ((uint64_t *)MIB.AccessHistogram)[J] =
+          endian::readNext<uint64_t, llvm::endianness::little, unaligned>(Ptr);
     }
     Items.push_back({Id, MIB});
   }
   return Items;
 }
 
-llvm::SmallVector<std::pair<uint64_t, MemInfoBlock>>
-readMemInfoBlocksV4(const char *Ptr) {
-  return readMemInfoBlocksCommon(Ptr);
-}
-
-llvm::SmallVector<std::pair<uint64_t, MemInfoBlock>>
-readMemInfoBlocksV5(const char *Ptr) {
-  return readMemInfoBlocksCommon(Ptr, /*IsHistogramEncoded=*/true);
-}
-
 CallStackMap readStackInfo(const char *Ptr) {
   using namespace support;
 
@@ -674,8 +658,6 @@ RawMemProfReader::readMemInfoBlocks(const char *Ptr) {
     return readMemInfoBlocksV3(Ptr);
   if (MemprofRawVersion == 4ULL)
     return readMemInfoBlocksV4(Ptr);
-  if (MemprofRawVersion == 5ULL)
-    return readMemInfoBlocksV5(Ptr);
   llvm_unreachable(
       "Panic: Unsupported version number when reading MemInfoBlocks");
 }