[BOLT] Remove unneeded dyncasts

[urnathan]

Summary

AFAICT these dyncasts cannot fail -- we've already checked the ELF format when loading up the executable, and will have already bailed there if there was a mismatch.

[rafauler]

LGTM

bolt/lib/Rewrite/RewriteInstance.cpp

static bool shouldDisassemble(const BinaryFunction &BF) {
 
   return !BF.isIgnored();
 }
 
 Error RewriteInstance::discoverStorage() {
   NamedRegionTimer T("discoverStorage", "discover storage", TimerGroupName,
                      TimerGroupDesc, opts::TimeRewrite);
 
-  auto ELF64LEFile = dyn_cast<ELF64LEObjectFile>(InputFile);
+  auto ELF64LEFile = cast<ELF64LEObjectFile>(InputFile);
   const ELFFile<ELF64LE> &Obj = ELF64LEFile->getELFFile();
 
   BC->StartFunctionAddress = Obj.getHeader().e_entry;
 
   NextAvailableAddress = 0;
   uint64_t NextAvailableOffset = 0;
   Expected<ELF64LE::PhdrRange> PHsOrErr = Obj.program_headers();
   if (Error E = PHsOrErr.takeError())

 }
 
 void RewriteInstance::updateOutputValues(const MCAsmLayout &Layout) {
   for (BinaryFunction *Function : BC->getAllBinaryFunctions())
     Function->updateOutputValues(Layout);
 }
 
 void RewriteInstance::patchELFPHDRTable() {
-  auto ELF64LEFile = dyn_cast<ELF64LEObjectFile>(InputFile);
-  if (!ELF64LEFile) {
-    errs() << "BOLT-ERROR: only 64-bit LE ELF binaries are supported\n";
-    exit(1);
-  }
+  auto ELF64LEFile = cast<ELF64LEObjectFile>(InputFile);
   const ELFFile<ELF64LE> &Obj = ELF64LEFile->getELFFile();
   raw_fd_ostream &OS = Out->os();
 
   // Write/re-write program headers.
   Phnum = Obj.getHeader().e_phnum;
   if (PHDRTableOffset) {
     // Writing new pheader table and adding one new entry for R+X segment.
     Phnum += 1;
uint64_t appendPadding(raw_pwrite_stream &OS, uint64_t Offset,
   for (unsigned I = 0; I < PaddingSize; ++I)
     OS.write((unsigned char)0);
   return Offset + PaddingSize;
 }
 
 }
 
 void RewriteInstance::rewriteNoteSections() {
-  auto ELF64LEFile = dyn_cast<ELF64LEObjectFile>(InputFile);
-  if (!ELF64LEFile) {
-    errs() << "BOLT-ERROR: only 64-bit LE ELF binaries are supported\n";
-    exit(1);
-  }
+  auto ELF64LEFile = cast<ELF64LEObjectFile>(InputFile);
   const ELFFile<ELF64LE> &Obj = ELF64LEFile->getELFFile();
   raw_fd_ostream &OS = Out->os();
 
   uint64_t NextAvailableOffset = getFileOffsetForAddress(NextAvailableAddress);
   assert(NextAvailableOffset >= FirstNonAllocatableOffset &&
          "next available offset calculation failure");
   OS.seek(NextAvailableOffset);