Initialize OffsetMap earlier

[• espindola]

Summary

Sorry for the noise, but now that getSectionPiece uses OffsetMap, it is advantageous to initialize it earlier.

It is also the simplest so far.

[ruiu]

LGTM

Nice!

[• espindola]

r329242

ELF/InputSection.cpp

 void MergeInputSection::splitIntoPieces() {
   assert(Pieces.empty());
 
   if (Flags & SHF_STRINGS)
     splitStrings(Data, Entsize);
   else
     splitNonStrings(Data, Entsize);
 
+  OffsetMap.reserve(Pieces.size());
+  for (size_t I = 0, E = Pieces.size(); I != E; ++I)
+    OffsetMap[Pieces[I].InputOff] = I;
+
   if (Config->GcSections && (Flags & SHF_ALLOC))
     for (uint32_t Off : LiveOffsets)
       getSectionPiece(Off)->Live = true;
 }
 
 template <class It, class T, class Compare>
 static It fastUpperBound(It First, It Last, const T &Value, Compare Comp) {
   size_t Size = std::distance(First, Last);

ELF/SyntheticSections.cpp

for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
         Builder.add(Sec->getData(I));
 
   // Fix the string table content. After this, the contents will never change.
   Builder.finalize();
 
   // finalize() fixed tail-optimized strings, so we can now get
   // offsets of strings. Get an offset for each string and save it
   // to a corresponding StringPiece for easy access.
-  for (MergeInputSection *Sec : Sections) {
-    Sec->OffsetMap.reserve(Sec->Pieces.size());
-    for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I) {
-      SectionPiece &P = Sec->Pieces[I];
-      Sec->OffsetMap[P.InputOff] = I;
-      if (P.Live)
-        P.OutputOff = Builder.getOffset(Sec->getData(I));
-    }
-  }
+  for (MergeInputSection *Sec : Sections)
+    for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
+      if (Sec->Pieces[I].Live)
+        Sec->Pieces[I].OutputOff = Builder.getOffset(Sec->getData(I));
 }
 
 void MergeNoTailSection::writeTo(uint8_t *Buf) {
   for (size_t I = 0; I < NumShards; ++I)
     Shards[I].write(Buf + ShardOffsets[I]);
 }
 
 // This function is very hot (i.e. it can take several seconds to finish)
for (size_t I = 0; I < NumShards; ++I) {
     ShardOffsets[I] = Off;
     Off += Shards[I].getSize();
   }
   Size = Off;
 
   // So far, section pieces have offsets from beginning of shards, but
   // we want offsets from beginning of the whole section. Fix them.
   parallelForEach(Sections, [&](MergeInputSection *Sec) {
-    Sec->OffsetMap.reserve(Sec->Pieces.size());
-    for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I) {
-      SectionPiece &P = Sec->Pieces[I];
-      Sec->OffsetMap[P.InputOff] = I;
-      if (P.Live)
-        P.OutputOff += ShardOffsets[getShardId(P.Hash)];
-    }
+    for (size_t I = 0, E = Sec->Pieces.size(); I != E; ++I)
+      if (Sec->Pieces[I].Live)
+        Sec->Pieces[I].OutputOff +=
+            ShardOffsets[getShardId(Sec->Pieces[I].Hash)];
   });
 }
 
 static MergeSyntheticSection *createMergeSynthetic(StringRef Name,
                                                    uint32_t Type,
                                                    uint64_t Flags,
                                                    uint32_t Alignment) {
   bool ShouldTailMerge = (Flags & SHF_STRINGS) && Config->Optimize >= 2;