[llvm-objdump] - Introduce getRelocsMap() helper. NFCI.

[grimar]

Summary

Currently disassembleObject() is a ~550 lines length function.
This patch extracts the code that creates a section->its relocation
mapping into a new helper function to simplify/reduce it a bit.

[jhenderson]

LGTM. I would sound a note of caution that disassembly performance is important, but it looks like this has the potential to improve it!

tools/llvm-objdump/llvm-objdump.cpp

871

to its -> to their

tools/llvm-objdump/llvm-objdump.cpp

static size_t countSkippableZeroBytes(ArrayRef<uint8_t> Buf) {
   if (N < 8)
     return 0;
 
   // We skip zeroes in multiples of 4 because do not want to truncate an
   // instruction if it starts with a zero byte.
   return N & ~0x3;
 }
 
+// Returns a map from sections to its relocations.
+static std::map<SectionRef, std::vector<RelocationRef>>
+getRelocsMap(llvm::object::ObjectFile const &Obj) {
+  std::map<SectionRef, std::vector<RelocationRef>> Ret;
+  for (const SectionRef &Section : ToolSectionFilter(Obj)) {
+    section_iterator RelSec = Section.getRelocatedSection();
+    if (RelSec == Obj.section_end())
+      continue;
+    std::vector<RelocationRef> &V = Ret[*RelSec];
+    for (const RelocationRef &R : Section.relocations())
+      V.push_back(R);
+    // Sort relocations by address.
+    llvm::sort(V, isRelocAddressLess);
+  }
+  return Ret;
+}
+
 static void disassembleObject(const ObjectFile *Obj, bool InlineRelocs) {
   if (StartAddress > StopAddress)
     error("Start address should be less than stop address");
 
   const Target *TheTarget = getTarget(Obj);
 
   // Package up features to be passed to target/subtarget
   SubtargetFeatures Features = Obj->getFeatures();
static void disassembleObject(const ObjectFile *Obj, bool InlineRelocs) {
   IP->setPrintImmHex(PrintImmHex);
   PrettyPrinter &PIP = selectPrettyPrinter(Triple(TripleName));
 
   StringRef Fmt = Obj->getBytesInAddress() > 4 ? "\t\t%016" PRIx64 ":  " :
                                                  "\t\t\t%08" PRIx64 ":  ";
 
   SourcePrinter SP(Obj, TheTarget->getName());
 
-  // Create a mapping, RelocSecs = SectionRelocMap[S], where sections
-  // in RelocSecs contain the relocations for section S.
-  std::error_code EC;
-  std::map<SectionRef, SmallVector<SectionRef, 1>> SectionRelocMap;
-  for (const SectionRef &Section : ToolSectionFilter(*Obj)) {
-    section_iterator Sec2 = Section.getRelocatedSection();
-    if (Sec2 != Obj->section_end())
-      SectionRelocMap[*Sec2].push_back(Section);
-  }
+  std::map<SectionRef, std::vector<RelocationRef>> RelocMap;
+  if (InlineRelocs)
+    RelocMap = getRelocsMap(*Obj);
 
   // Create a mapping from virtual address to symbol name.  This is used to
   // pretty print the symbols while disassembling.
   std::map<SectionRef, SectionSymbolsTy> AllSymbols;
   SectionSymbolsTy AbsoluteSymbols;
   for (const SymbolRef &Symbol : Obj->symbols()) {
     Expected<uint64_t> AddressOrErr = Symbol.getAddress();
     if (!AddressOrErr)
if (Obj->isELF() && Obj->getArch() == Triple::amdgcn) {
       if (RelInfo) {
         std::unique_ptr<MCSymbolizer> Symbolizer(
           TheTarget->createMCSymbolizer(
             TripleName, nullptr, nullptr, &Symbols, &Ctx, std::move(RelInfo)));
         DisAsm->setSymbolizer(std::move(Symbolizer));
       }
     }
 
-    // Make a list of all the relocations for this section.
-    std::vector<RelocationRef> Rels;
-    if (InlineRelocs) {
-      for (const SectionRef &RelocSec : SectionRelocMap[Section]) {
-        for (const RelocationRef &Reloc : RelocSec.relocations()) {
-          Rels.push_back(Reloc);
-        }
-      }
-    }
-
-    // Sort relocations by address.
-    llvm::sort(Rels, isRelocAddressLess);
-
     StringRef SegmentName = "";
     if (const MachOObjectFile *MachO = dyn_cast<const MachOObjectFile>(Obj)) {
       DataRefImpl DR = Section.getRawDataRefImpl();
       SegmentName = MachO->getSectionFinalSegmentName(DR);
     }
     StringRef SectionName;
     error(Section.getName(SectionName));
 
for (const SectionRef &Section : ToolSectionFilter(*Obj)) {
     error(Section.getContents(BytesStr));
     ArrayRef<uint8_t> Bytes(reinterpret_cast<const uint8_t *>(BytesStr.data()),
                             BytesStr.size());
 
     uint64_t Size;
     uint64_t Index;
     bool PrintedSection = false;
 
+    std::vector<RelocationRef> Rels = RelocMap[Section];
     std::vector<RelocationRef>::const_iterator RelCur = Rels.begin();
     std::vector<RelocationRef>::const_iterator RelEnd = Rels.end();
     // Disassemble symbol by symbol.
     for (unsigned SI = 0, SE = Symbols.size(); SI != SE; ++SI) {
       uint64_t Start = std::get<0>(Symbols[SI]) - SectionAddr;
       // The end is either the section end or the beginning of the next
       // symbol.
       uint64_t End = (SI == SE - 1)