MC: Remove redundant substr() call

[sbc100]

ping

[thegameg]

This somehow broke a stage-2 GreenDragon: http://green.lab.llvm.org/green/job/clang-stage2-Rthinlto/10387/ (it might not be the issue, though)

I noticed one small issue with the code but I'm not sure if any callers rely on that. Comment below.

[thegameg]

llvm/trunk/lib/Object/MachOObjectFile.cpp

110

.substr never goes past end if Offset > getData().size(). Maybe add an assert to make sure no callers rely on this?

[sbc100]

llvm/trunk/lib/Object/MachOObjectFile.cpp

110

Good point, I was trying to figure out what the original intention was and I guess that may have been it. But it doesn't make a lot of sense to me.. from looking at the StringRef::substr code it looks like it will always return a pointer to the end of the string if you request and out of bounds offset, then the code the receives this pointer will read out of bounds just off the end of the string. I can't see why this would be useful or desired. But adding an assert would certainly be an improvement. I will do that.

Do you think this change could be responsible for the build break you are seeing? I can't really see how it could break anything that wasn't already very broken. But I could be missing something.

[thegameg]

llvm/trunk/lib/Object/MachOObjectFile.cpp

110

Thanks! For the build, nothing obvious comes to mind, once I'll be able to reproduce locally I'll let you know.

[thegameg]

llvm/trunk/lib/Object/MachOObjectFile.cpp

110

Nope, reverted this locally and I can still see the fail. Sorry for the false alarm.

llvm/trunk/lib/Object/MachOObjectFile.cpp

getSectionPtr(const MachOObjectFile &O, MachOObjectFile::LoadCommandInfo L,
   unsigned SectionSize = Is64 ? sizeof(MachO::section_64) :
                                 sizeof(MachO::section);
 
   uintptr_t SectionAddr = CommandAddr + SegmentLoadSize + Sec * SectionSize;
   return reinterpret_cast<const char*>(SectionAddr);
 }
 
 static const char *getPtr(const MachOObjectFile &O, size_t Offset) {
-  return O.getData().substr(Offset, 1).data();
+  return O.getData().data() + Offset;
 }
 
 static MachO::nlist_base
 getSymbolTableEntryBase(const MachOObjectFile &O, DataRefImpl DRI) {
   const char *P = reinterpret_cast<const char *>(DRI.p);
   return getStruct<MachO::nlist_base>(O, P);
 }
 

llvm/trunk/lib/Object/WasmObjectFile.cpp

Error WasmObjectFile::parseDataSection(ReadContext &Ctx) {
   }
   if (Ctx.Ptr != Ctx.End)
     return make_error<GenericBinaryError>("Data section ended prematurely",
                                           object_error::parse_failed);
   return Error::success();
 }
 
 const uint8_t *WasmObjectFile::getPtr(size_t Offset) const {
-  return reinterpret_cast<const uint8_t *>(getData().substr(Offset, 1).data());
+  return reinterpret_cast<const uint8_t *>(getData().data() + Offset);
 }
 
 const wasm::WasmObjectHeader &WasmObjectFile::getHeader() const {
   return Header;
 }
 
 void WasmObjectFile::moveSymbolNext(DataRefImpl &Symb) const { Symb.d.a++; }