Minor Instr PGO code restructuring

1. Key constant values (version, magic) and data structures related to raw and 
   indexed profile format are moved into one centralized file: InstrProf.h.
2. Utility function such as MD5Hash computation is also moved to the common 
   header to allow sharing with other components in the future.
3. A header data structure is introduced for Indexed format so that the reader
   and writer can always be in sync.
4. Added some comments to document different places where multiple definition
   of the data structure must be kept in sync (reader/writer, runtime, lowering 
   etc).  No functional change is intended.

Differential Revision:  http://reviews.llvm.org/D13758

llvm-svn: 250638

1 files changed, 15 insertions, 5 deletions

diff --git a/llvm/lib/ProfileData/InstrProfWriter.cpp b/llvm/lib/ProfileData/InstrProfWriter.cpp
index 856194d7..e3018a9 100644
--- a/llvm/lib/ProfileData/InstrProfWriter.cpp
+++ b/llvm/lib/ProfileData/InstrProfWriter.cpp
@@ -13,7 +13,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ProfileData/InstrProfWriter.h"
-#include "InstrProfIndexed.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/EndianStream.h"
 #include "llvm/Support/OnDiskHashTable.h"
@@ -197,13 +196,23 @@ std::pair<uint64_t, uint64_t> InstrProfWriter::writeImpl(raw_ostream &OS) {
   endian::Writer<little> LE(OS);
 
   // Write the header.
-  LE.write<uint64_t>(IndexedInstrProf::Magic);
-  LE.write<uint64_t>(IndexedInstrProf::Version);
-  LE.write<uint64_t>(MaxFunctionCount);
-  LE.write<uint64_t>(static_cast<uint64_t>(IndexedInstrProf::HashType));
+  IndexedInstrProf::Header Header;
+  Header.Magic = IndexedInstrProf::Magic;
+  Header.Version = IndexedInstrProf::Version;
+  Header.MaxFunctionCount = MaxFunctionCount;
+  Header.HashType = static_cast<uint64_t>(IndexedInstrProf::HashType);
+  Header.HashOffset = 0;
+  int N = sizeof(IndexedInstrProf::Header) / sizeof(uint64_t);
+
+  // Only write out all the fields execpt 'HashOffset'. We need
+  // to remember the offset of that field to allow back patching
+  // later.
+  for (int I = 0; I < N - 1; I++)
+    LE.write<uint64_t>(reinterpret_cast<uint64_t *>(&Header)[I]);
 
   // Save a space to write the hash table start location.
   uint64_t HashTableStartLoc = OS.tell();
+  // Reserve the space for HashOffset field.
   LE.write<uint64_t>(0);
   // Write the hash table.
   uint64_t HashTableStart = Generator.Emit(OS);
@@ -218,6 +227,7 @@ void InstrProfWriter::write(raw_fd_ostream &OS) {
   // Go back and fill in the hash table start.
   using namespace support;
   OS.seek(TableStart.first);
+  // Now patch the HashOffset field previously reserved.
   endian::Writer<little>(OS).write<uint64_t>(TableStart.second);
 }