Provide a fast "get me the target triple from the module" API. This can

drastically reduce the linking time during LTO.

Patch by Shantonu Sen!

llvm-svn: 115728

include/llvm/Bitcode/ReaderWriter.h

@@ -33,6 +33,15 @@ namespace llvm {
                                LLVMContext& Context,
                                std::string *ErrMsg = 0);
 
+  /// getBitcodeTargetTriple - Read the header of the specified bitcode
+  /// buffer and extract just the triple information. If successful,
+  /// this returns a string and *does not* take ownership
+  /// of 'buffer'. On error, this returns "", and fills in *ErrMsg
+  /// if ErrMsg is non-null.
+  std::string getBitcodeTargetTriple(MemoryBuffer *Buffer,
+				     LLVMContext& Context,
+				     std::string *ErrMsg = 0);
+
   /// ParseBitcodeFile - Read the specified bitcode file, returning the module.
   /// If an error occurs, this returns null and fills in *ErrMsg if it is
   /// non-null.  This method *never* takes ownership of Buffer.

lib/Bitcode/Reader/BitcodeReader.cpp

@@ -1600,6 +1600,112 @@ bool BitcodeReader::ParseBitcodeInto(Module *M) {
   return false;
 }
 
+bool BitcodeReader::ParseModuleTriple(std::string &Triple) {
+  if (Stream.EnterSubBlock(bitc::MODULE_BLOCK_ID))
+    return Error("Malformed block record");
+
+  SmallVector<uint64_t, 64> Record;
+
+  // Read all the records for this module.
+  while (!Stream.AtEndOfStream()) {
+    unsigned Code = Stream.ReadCode();
+    if (Code == bitc::END_BLOCK) {
+      if (Stream.ReadBlockEnd())
+        return Error("Error at end of module block");
+
+      return false;
+    }
+
+    if (Code == bitc::ENTER_SUBBLOCK) {
+      switch (Stream.ReadSubBlockID()) {
+      default:  // Skip unknown content.
+        if (Stream.SkipBlock())
+          return Error("Malformed block record");
+        break;
+      }
+      continue;
+    }
+
+    if (Code == bitc::DEFINE_ABBREV) {
+      Stream.ReadAbbrevRecord();
+      continue;
+    }
+
+    // Read a record.
+    switch (Stream.ReadRecord(Code, Record)) {
+    default: break;  // Default behavior, ignore unknown content.
+    case bitc::MODULE_CODE_VERSION:  // VERSION: [version#]
+      if (Record.size() < 1)
+        return Error("Malformed MODULE_CODE_VERSION");
+      // Only version #0 is supported so far.
+      if (Record[0] != 0)
+        return Error("Unknown bitstream version!");
+      break;
+    case bitc::MODULE_CODE_TRIPLE: {  // TRIPLE: [strchr x N]
+      std::string S;
+      if (ConvertToString(Record, 0, S))
+        return Error("Invalid MODULE_CODE_TRIPLE record");
+      Triple = S;
+      break;
+    }
+    }
+    Record.clear();
+  }
+
+  return Error("Premature end of bitstream");
+}
+
+bool BitcodeReader::ParseTriple(std::string &Triple) {
+  if (Buffer->getBufferSize() & 3)
+    return Error("Bitcode stream should be a multiple of 4 bytes in length");
+
+  unsigned char *BufPtr = (unsigned char *)Buffer->getBufferStart();
+  unsigned char *BufEnd = BufPtr+Buffer->getBufferSize();
+
+  // If we have a wrapper header, parse it and ignore the non-bc file contents.
+  // The magic number is 0x0B17C0DE stored in little endian.
+  if (isBitcodeWrapper(BufPtr, BufEnd))
+    if (SkipBitcodeWrapperHeader(BufPtr, BufEnd))
+      return Error("Invalid bitcode wrapper header");
+
+  StreamFile.init(BufPtr, BufEnd);
+  Stream.init(StreamFile);
+
+  // Sniff for the signature.
+  if (Stream.Read(8) != 'B' ||
+      Stream.Read(8) != 'C' ||
+      Stream.Read(4) != 0x0 ||
+      Stream.Read(4) != 0xC ||
+      Stream.Read(4) != 0xE ||
+      Stream.Read(4) != 0xD)
+    return Error("Invalid bitcode signature");
+
+  // We expect a number of well-defined blocks, though we don't necessarily
+  // need to understand them all.
+  while (!Stream.AtEndOfStream()) {
+    unsigned Code = Stream.ReadCode();
+
+    if (Code != bitc::ENTER_SUBBLOCK)
+      return Error("Invalid record at top-level");
+
+    unsigned BlockID = Stream.ReadSubBlockID();
+
+    // We only know the MODULE subblock ID.
+    switch (BlockID) {
+    case bitc::MODULE_BLOCK_ID:
+      if (ParseModuleTriple(Triple))
+        return true;
+      break;
+    default:
+      if (Stream.SkipBlock())
+        return Error("Malformed block record");
+      break;
+    }
+  }
+
+  return false;
+}
+
 /// ParseMetadataAttachment - Parse metadata attachments.
 bool BitcodeReader::ParseMetadataAttachment() {
   if (Stream.EnterSubBlock(bitc::METADATA_ATTACHMENT_ID))
@@ -2537,7 +2643,24 @@ Module *llvm::ParseBitcodeFile(MemoryBuffer *Buffer, LLVMContext& Context,
   // Read in the entire module, and destroy the BitcodeReader.
   if (M->MaterializeAllPermanently(ErrMsg)) {
     delete M;
-    return NULL;
+    return 0;
   }
+
   return M;
 }
+
+std::string llvm::getBitcodeTargetTriple(MemoryBuffer *Buffer,
+                                         LLVMContext& Context,
+                                         std::string *ErrMsg) {
+  BitcodeReader *R = new BitcodeReader(Buffer, Context);
+  // Don't let the BitcodeReader dtor delete 'Buffer'.
+  R->setBufferOwned(false);
+
+  std::string Triple("");
+  if (R->ParseTriple(Triple))
+    if (ErrMsg)
+      *ErrMsg = R->getErrorString();
+
+  delete R;
+  return Triple;
+}

lib/Bitcode/Reader/BitcodeReader.h

@@ -212,6 +212,10 @@ public:
   /// @brief Main interface to parsing a bitcode buffer.
   /// @returns true if an error occurred.
   bool ParseBitcodeInto(Module *M);
+
+  /// @brief Cheap mechanism to just extract module triple
+  /// @returns true if an error occurred.
+  bool ParseTriple(std::string &Triple);
 private:
   const Type *getTypeByID(unsigned ID, bool isTypeTable = false);
   Value *getFnValueByID(unsigned ID, const Type *Ty) {
@@ -270,6 +274,7 @@ private:
   bool ResolveGlobalAndAliasInits();
   bool ParseMetadata();
   bool ParseMetadataAttachment();
+  bool ParseModuleTriple(std::string &Triple);
 };
   
 } // End llvm namespace

tools/lto/LTOModule.cpp

@@ -64,15 +64,10 @@ bool LTOModule::isBitcodeFileForTarget(const char *path,
 
 // Takes ownership of buffer.
 bool LTOModule::isTargetMatch(MemoryBuffer *buffer, const char *triplePrefix) {
-  OwningPtr<Module> m(getLazyBitcodeModule(buffer, getGlobalContext()));
-  // On success, m owns buffer and both are deleted at end of this method.
-  if (!m) {
-    delete buffer;
-    return false;
-  }
-  std::string actualTarget = m->getTargetTriple();
-  return (strncmp(actualTarget.c_str(), triplePrefix,
-                  strlen(triplePrefix)) == 0);
+  std::string Triple = getBitcodeTargetTriple(buffer, getGlobalContext());
+  delete buffer;
+  return (strncmp(Triple.c_str(), triplePrefix, 
+ 		  strlen(triplePrefix)) == 0);
 }