<div dir="ltr">This seems a binary search, so how it is different from std::upper_bound?</div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Oct 19, 2016 at 7:17 AM, Rafael Espindola via llvm-commits <span dir="ltr"><<a href="mailto:llvm-commits@lists.llvm.org" target="_blank">llvm-commits@lists.llvm.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Author: rafael<br>
Date: Wed Oct 19 09:17:36 2016<br>
New Revision: 284594<br>
<br>
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=284594&view=rev" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project?rev=284594&view=rev</a><br>
Log:<br>
Add a faster binary search.<br>
<br>
Even with the hash table cache, binary search was still pretty<br>
hot. This can be made even faster with prefetching.<br>
<br>
Idea from <a href="http://cglab.ca/~morin/misc/arraylayout-v2/" rel="noreferrer" target="_blank">http://cglab.ca/~morin/misc/<wbr>arraylayout-v2/</a><br>
<br>
I will suggest moving this to llvm.<br>
<br>
Modified:<br>
    lld/trunk/ELF/InputSection.cpp<br>
<br>
Modified: lld/trunk/ELF/InputSection.cpp<br>
URL: <a href="http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=284594&r1=284593&r2=284594&view=diff" rel="noreferrer" target="_blank">http://llvm.org/viewvc/llvm-<wbr>project/lld/trunk/ELF/<wbr>InputSection.cpp?rev=284594&<wbr>r1=284593&r2=284594&view=diff</a><br>
==============================<wbr>==============================<wbr>==================<br>
--- lld/trunk/ELF/InputSection.cpp (original)<br>
+++ lld/trunk/ELF/InputSection.cpp Wed Oct 19 09:17:36 2016<br>
@@ -651,6 +651,19 @@ SectionPiece *MergeInputSection<ELFT>::g<br>
   return const_cast<SectionPiece *>(This->getSectionPiece(<wbr>Offset));<br>
 }<br>
<br>
+template <class It, class T, class Compare><br>
+static It fastUpperBound(It First, It Last, const T &Value, Compare Comp) {<br>
+  size_t Size = std::distance(First, Last);<br>
+  assert(Size != 0);<br>
+  while (Size != 1) {<br>
+    size_t H = Size / 2;<br>
+    const It MI = First + H;<br>
+    Size -= H;<br>
+    First = Comp(Value, *MI) ? First : First + H;<br>
+  }<br>
+  return Comp(Value, *First) ? First : First + 1;<br>
+}<br>
+<br>
 template <class ELFT><br>
 const SectionPiece *<br>
 MergeInputSection<ELFT>::<wbr>getSectionPiece(uintX_t Offset) const {<br>
@@ -659,7 +672,7 @@ MergeInputSection<ELFT>::<wbr>getSectionPiece<br>
     fatal(getName(this) + ": entry is past the end of the section");<br>
<br>
   // Find the element this offset points to.<br>
-  auto I = std::upper_bound(<br>
+  auto I = fastUpperBound(<br>
       Pieces.begin(), Pieces.end(), Offset,<br>
       [](const uintX_t &A, const SectionPiece &B) { return A < B.InputOff; });<br>
   --I;<br>
<br>
<br>
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</blockquote></div><br></div>