From 584abaee676dfe43848c5b93133e6737ace3d408 Mon Sep 17 00:00:00 2001
From: Rui Ueyama <ruiu@google.com>
Date: Fri, 27 Feb 2015 05:05:38 +0000
Subject: [PATCH] PECOFF: Do not add layout-after edges.

Previously we needed to create atoms as a doubly-linked link, but it's
no longer needed. Also we don't use layout-after edges in PE/COFF.
Creating such edges is just waste.

llvm-svn: 230732
---
 lld/lib/ReaderWriter/PECOFF/Atoms.h        | 23 ++++++----------------
 lld/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp |  2 +-
 2 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/lld/lib/ReaderWriter/PECOFF/Atoms.h b/lld/lib/ReaderWriter/PECOFF/Atoms.h
index f66920713964..5d101962411a 100644
--- a/lld/lib/ReaderWriter/PECOFF/Atoms.h
+++ b/lld/lib/ReaderWriter/PECOFF/Atoms.h
@@ -351,27 +351,16 @@ void addLayoutEdge(T *a, U *b, uint32_t which) {
   a->addReference(std::unique_ptr<COFFReference>(ref));
 }
 
-template <typename T, typename U> void connectWithLayoutEdge(T *a, U *b) {
-  addLayoutEdge(a, b, lld::Reference::kindLayoutAfter);
-  addLayoutEdge(b, a, lld::Reference::kindLayoutBefore);
-}
-
-/// Connect atoms with layout-{before,after} edges. It usually serves two
-/// purposes.
-///
-///   - To prevent atoms from being GC'ed (aka dead-stripped) if there is a
-///     reference to one of the atoms. In that case we want to emit all the
-///     atoms appeared in the same section, because the referenced "live" atom
-///     may reference other atoms in the same section. If we don't add layout
-///     edges between atoms, unreferenced atoms in the same section would be
-///     GC'ed.
-///   - To preserve the order of atmos. We want to emit the atoms in the
-///     same order as they appeared in the input object file.
+/// Connect atoms with layout-before edges. It prevents atoms from
+/// being GC'ed (aka dead-stripped) if there is a reference to one of
+/// the atoms in the same layout-before chain. In such case we want to
+/// emit all the atoms appeared in the same chain, because the "live"
+/// atom may reference other atoms in the same chain.
 template <typename T> void connectAtomsWithLayoutEdge(std::vector<T *> &atoms) {
   if (atoms.size() < 2)
     return;
   for (auto it = atoms.begin(), e = atoms.end(); it + 1 != e; ++it)
-    connectWithLayoutEdge(*it, *(it + 1));
+    addLayoutEdge(*(it + 1), *it, lld::Reference::kindLayoutBefore);
 }
 
 } // namespace pecoff
diff --git a/lld/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp b/lld/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
index 171137713c5e..c42d3c2db9d3 100644
--- a/lld/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
+++ b/lld/lib/ReaderWriter/PECOFF/ReaderCOFF.cpp
@@ -756,7 +756,7 @@ std::error_code FileCOFF::AtomizeDefinedSymbols(
     if (atoms.size() > 0)
       atoms[0]->setAlignment(getAlignment(section));
 
-    // Connect atoms with layout-before/layout-after edges.
+    // Connect atoms with layout-before edges.
     connectAtomsWithLayoutEdge(atoms);
 
     for (COFFDefinedFileAtom *atom : atoms) {