[lld] r270572 - Do not start over relocation search from beginning.

[Rui Ueyama via llvm-commits]

Author: ruiu
Date: Tue May 24 10:40:46 2016
New Revision: 270572

URL: http://llvm.org/viewvc/llvm-project?rev=270572&view=rev
Log:
Do not start over relocation search from beginning.

This patch addresses a post-commit review for r270325. r270325
introduced getReloc function that searches a relocation for a
given range. It always started searching from beginning of relocation
vector, so it was slower than before. Previously, we used to use
the fact that the relocations are sorted. This patch restore it.

Modified:
    lld/trunk/ELF/OutputSections.cpp
    lld/trunk/ELF/OutputSections.h

Modified: lld/trunk/ELF/OutputSections.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.cpp?rev=270572&r1=270571&r2=270572&view=diff
==============================================================================
--- lld/trunk/ELF/OutputSections.cpp (original)
+++ lld/trunk/ELF/OutputSections.cpp Tue May 24 10:40:46 2016
@@ -920,14 +920,21 @@ void EhOutputSection<ELFT>::forEachInput
 // Returns the first relocation that points to a region
 // between Begin and Begin+Size.
 template <class IntTy, class RelTy>
-static const RelTy *getReloc(IntTy Begin, IntTy Size, ArrayRef<RelTy> Rels) {
-  size_t I = 0;
-  size_t E = Rels.size();
-  while (I != E && Rels[I].r_offset < Begin)
-    ++I;
-  if (I == E || Begin + Size <= Rels[I].r_offset)
+static const RelTy *getReloc(IntTy Begin, IntTy Size, ArrayRef<RelTy> &Rels) {
+  for (auto I = Rels.begin(), E = Rels.end(); I != E; ++I) {
+    if (I->r_offset < Begin)
+      continue;
+
+    // Truncate Rels for fast access. That means we expect that the
+    // relocations are sorted and we are looking up symbols in
+    // sequential order. It is naturally satisfied for .eh_frame.
+    Rels = Rels.slice(I - Rels.begin());
+    if (I->r_offset < Begin + Size)
+      return I;
     return nullptr;
-  return &Rels[I];
+  }
+  Rels = ArrayRef<RelTy>();
+  return nullptr;
 }
 
 // Search for an existing CIE record or create a new one.
@@ -937,7 +944,7 @@ template <class ELFT>
 template <class RelTy>
 CieRecord *EhOutputSection<ELFT>::addCie(SectionPiece &Piece,
                                          EhInputSection<ELFT> *Sec,
-                                         ArrayRef<RelTy> Rels) {
+                                         ArrayRef<RelTy> &Rels) {
   const endianness E = ELFT::TargetEndianness;
   if (read32<E>(Piece.Data.data() + 4) != 0)
     fatal("CIE expected at beginning of .eh_frame: " + Sec->getSectionName());
@@ -971,7 +978,7 @@ template <class ELFT>
 template <class RelTy>
 bool EhOutputSection<ELFT>::isFdeLive(SectionPiece &Piece,
                                       EhInputSection<ELFT> *Sec,
-                                      ArrayRef<RelTy> Rels) {
+                                      ArrayRef<RelTy> &Rels) {
   const RelTy *Rel = getReloc(Piece.InputOff, Piece.size(), Rels);
   if (!Rel)
     fatal("FDE doesn't reference another section");

Modified: lld/trunk/ELF/OutputSections.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/OutputSections.h?rev=270572&r1=270571&r2=270572&view=diff
==============================================================================
--- lld/trunk/ELF/OutputSections.h (original)
+++ lld/trunk/ELF/OutputSections.h Tue May 24 10:40:46 2016
@@ -357,11 +357,11 @@ private:
 
   template <class RelTy>
   CieRecord *addCie(SectionPiece &Piece, EhInputSection<ELFT> *Sec,
-                    ArrayRef<RelTy> Rels);
+                    ArrayRef<RelTy> &Rels);
 
   template <class RelTy>
   bool isFdeLive(SectionPiece &Piece, EhInputSection<ELFT> *Sec,
-                 ArrayRef<RelTy> Rels);
+                 ArrayRef<RelTy> &Rels);
 
   uintX_t getFdePc(uint8_t *Buf, size_t Off, uint8_t Enc);