[PATCH] [Object, MachO] Cache parsed MachO header in MachOObjectFile. NFC.

[Alexey Samsonov]

Hi rafael,

Avoid parsing object file each time MachOObjectFile::getHeader() is
called. Instead, cache the header in MachOObjectFile constructor, where
it's parsed anyway. In future, we must avoid constructing the object
at all if the header can't be parsed.

http://reviews.llvm.org/D10226

Files:
  include/llvm/Object/MachO.h
  lib/Object/MachOObjectFile.cpp

Index: include/llvm/Object/MachO.h
===================================================================
--- include/llvm/Object/MachO.h
+++ include/llvm/Object/MachO.h
@@ -385,8 +385,8 @@
 
   MachO::any_relocation_info getRelocation(DataRefImpl Rel) const;
   MachO::data_in_code_entry getDice(DataRefImpl Rel) const;
-  MachO::mach_header getHeader() const;
-  MachO::mach_header_64 getHeader64() const;
+  const MachO::mach_header &getHeader() const;
+  const MachO::mach_header_64 &getHeader64() const;
   uint32_t
   getIndirectSymbolTableEntry(const MachO::dysymtab_command &DLC,
                               unsigned Index) const;
@@ -433,6 +433,8 @@
   LoadCommandInfo getFirstLoadCommandInfo() const;
   LoadCommandInfo getNextLoadCommandInfo(const LoadCommandInfo &L) const;
 
+  MachO::mach_header_64 Header64;
+  MachO::mach_header *Header;  // Points inside Header64.
   typedef SmallVector<const char*, 1> SectionList;
   SectionList Sections;
   typedef SmallVector<const char*, 1> LibraryList;
Index: lib/Object/MachOObjectFile.cpp
===================================================================
--- lib/Object/MachOObjectFile.cpp
+++ lib/Object/MachOObjectFile.cpp
@@ -183,11 +183,18 @@
 MachOObjectFile::MachOObjectFile(MemoryBufferRef Object, bool IsLittleEndian,
                                  bool Is64bits, std::error_code &EC)
     : ObjectFile(getMachOType(IsLittleEndian, Is64bits), Object),
+      Header(reinterpret_cast<MachO::mach_header*>(&this->Header64)),
       SymtabLoadCmd(nullptr), DysymtabLoadCmd(nullptr),
       DataInCodeLoadCmd(nullptr), LinkOptHintsLoadCmd(nullptr),
       DyldInfoLoadCmd(nullptr), UuidLoadCmd(nullptr),
       HasPageZeroSegment(false) {
-  uint32_t LoadCommandCount = this->getHeader().ncmds;
+  // Parse header.
+  if (is64Bit())
+    Header64 = getStruct<MachO::mach_header_64>(this, getPtr(this, 0));
+  else
+    *Header = getStruct<MachO::mach_header>(this, getPtr(this, 0));
+
+  uint32_t LoadCommandCount = Header->ncmds;
   if (LoadCommandCount == 0)
     return;
 
@@ -1195,21 +1202,8 @@
 
 Triple MachOObjectFile::getArch(const char **McpuDefault,
                                 Triple *ThumbTriple) const {
-  Triple T;
-  if (is64Bit()) {
-    MachO::mach_header_64 H_64;
-    H_64 = getHeader64();
-    T = MachOObjectFile::getArch(H_64.cputype, H_64.cpusubtype, McpuDefault);
-    *ThumbTriple = MachOObjectFile::getThumbArch(H_64.cputype, H_64.cpusubtype,
-                                                 McpuDefault);
-  } else {
-    MachO::mach_header H;
-    H = getHeader();
-    T = MachOObjectFile::getArch(H.cputype, H.cpusubtype, McpuDefault);
-    *ThumbTriple = MachOObjectFile::getThumbArch(H.cputype, H.cpusubtype,
-                                                 McpuDefault);
-  }
-  return T;
+  *ThumbTriple = getThumbArch(Header->cputype, Header->cpusubtype, McpuDefault);
+  return getArch(Header->cputype, Header->cpusubtype, McpuDefault);
 }
 
 relocation_iterator MachOObjectFile::section_rel_begin(unsigned Index) const {
@@ -2164,12 +2158,13 @@
   return getStruct<MachO::data_in_code_entry>(this, P);
 }
 
-MachO::mach_header MachOObjectFile::getHeader() const {
-  return getStruct<MachO::mach_header>(this, getPtr(this, 0));
+const MachO::mach_header &MachOObjectFile::getHeader() const {
+  return *Header;
 }
 
-MachO::mach_header_64 MachOObjectFile::getHeader64() const {
-  return getStruct<MachO::mach_header_64>(this, getPtr(this, 0));
+const MachO::mach_header_64 &MachOObjectFile::getHeader64() const {
+  assert(is64Bit());
+  return Header64;
 }
 
 uint32_t MachOObjectFile::getIndirectSymbolTableEntry(

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