Allow public Triple deduction from ObjectFiles.

[hctim]

Summary

Move logic that allows for Triple deduction from an ObjectFile object out of llvm-objdump.cpp into a public factory, found in the ObjectFile class.

This should allow other tools in the future to use this logic without reimplementation.

[pcc]

Before considering this patch I would first like to see another client of the function that you are adding.

[hctim]

See D37937 for client.

[hctim]

Made ObjectFile::makeTriple() non-virtual. Removed braces around single line if-statement.

include/llvm/Object/ObjectFile.h

public:
   ///        file format.
   virtual uint8_t getBytesInAddress() const = 0;
 
   virtual StringRef getFileFormatName() const = 0;
   virtual /* Triple::ArchType */ unsigned getArch() const = 0;
   virtual SubtargetFeatures getFeatures() const = 0;
   virtual void setARMSubArch(Triple &TheTriple) const { }
 
+  /// @breif Create a triple from the data in this object file.
+  Triple makeTriple() const;
+
   /// Returns platform-specific object flags, if any.
   virtual std::error_code getPlatformFlags(unsigned &Result) const {
     Result = 0;
     return object_error::invalid_file_type;
   }
 
   virtual std::error_code
     getBuildAttributes(ARMAttributeParser &Attributes) const {

lib/Object/ObjectFile.cpp

if (!getSectionName(Sec, SectName))
     return SectName == ".llvmbc";
   return false;
 }
 
 section_iterator ObjectFile::getRelocatedSection(DataRefImpl Sec) const {
   return section_iterator(SectionRef(Sec, this));
 }
 
+Triple ObjectFile::makeTriple() const {
+  Triple TheTriple;
+  auto Arch = getArch();
+  TheTriple.setArch(Triple::ArchType(Arch));
+
+  // For ARM targets, try to use the build attributes to build determine
+  // the build target. Target features are also added, but later during
+  // disassembly.
+  if (Arch == Triple::arm || Arch == Triple::armeb)
+    setARMSubArch(TheTriple);
+
+  // TheTriple defaults to ELF, and COFF doesn't have an environment:
+  // the best we can do here is indicate that it is mach-o.
+  if (isMachO())
+    TheTriple.setObjectFormat(Triple::MachO);
+
+  if (isCOFF()) {
+    const auto COFFObj = dyn_cast<COFFObjectFile>(this);
+    if (COFFObj->getArch() == Triple::thumb)
+      TheTriple.setTriple("thumbv7-windows");
+  }
+
+  return TheTriple;
+}
+
 Expected<std::unique_ptr<ObjectFile>>
 ObjectFile::createObjectFile(MemoryBufferRef Object, file_magic Type) {
   StringRef Data = Object.getBuffer();
   if (Type == file_magic::unknown)
     Type = identify_magic(Data);
 
   switch (Type) {
   case file_magic::unknown:

tools/llvm-objdump/llvm-objdump.cpp

llvm::report_error(ArchiveName, NameOrErr.get(), std::move(E),
                        ArchitectureName);
 }
 
 static const Target *getTarget(const ObjectFile *Obj = nullptr) {
   // Figure out the target triple.
   llvm::Triple TheTriple("unknown-unknown-unknown");
   if (TripleName.empty()) {
     if (Obj) {
-      auto Arch = Obj->getArch();
-      TheTriple.setArch(Triple::ArchType(Arch));
-
-      // For ARM targets, try to use the build attributes to build determine
-      // the build target. Target features are also added, but later during
-      // disassembly.
-      if (Arch == Triple::arm || Arch == Triple::armeb) {
-        Obj->setARMSubArch(TheTriple);
-      }
-
-      // TheTriple defaults to ELF, and COFF doesn't have an environment:
-      // the best we can do here is indicate that it is mach-o.
-      if (Obj->isMachO())
-        TheTriple.setObjectFormat(Triple::MachO);
-
-      if (Obj->isCOFF()) {
-        const auto COFFObj = dyn_cast<COFFObjectFile>(Obj);
-        if (COFFObj->getArch() == Triple::thumb)
-          TheTriple.setTriple("thumbv7-windows");
-      }
+      TheTriple = Obj->makeTriple();
     }
   } else {
     TheTriple.setTriple(Triple::normalize(TripleName));
+
     // Use the triple, but also try to combine with ARM build attributes.
     if (Obj) {
       auto Arch = Obj->getArch();
       if (Arch == Triple::arm || Arch == Triple::armeb) {
         Obj->setARMSubArch(TheTriple);
       }
     }
   }