ELF: Don't use LayoutPass.

Previously we applied the LayoutPass to order atoms and then
apply elf::ArrayOrderPass to sort them again. The first pass is
basically supposed to sort atoms in the normal fashion (which
is to sort symbols in the same order as the input files).
The second pass sorts atoms in {init,fini}_array.<priority> by
priority.

The problem is that the LayoutPass is overkill. It analyzes
references between atoms to make a decision how to sort them.
It's slow, hard to understand, and above all, it doesn't seem
that we need its feature for ELF in the first place.

This patch remove the LayoutPass from ELF pass list. Now all
reordering is done in elf::OrderPass. That pass sorts atoms by
{init,fini}_array, and if they are not in the special section,
they are ordered as the same order as they appear in the command
line. The new code is far easier to understand, faster, and
still able to create valid executables.

Unlike the previous layout pass, elf::OrderPass doesn't count
any attributes of an atom (e.g. permissions) except its
position. It's OK because the writer takes care of them if we
have to.

This patch changes the order of final output, although that's
benign. Tests are updated.

http://reviews.llvm.org/D7278

llvm-svn: 227666

1 files changed, 0 insertions, 56 deletions

diff --git a/lld/lib/ReaderWriter/ELF/ArrayOrderPass.cpp b/lld/lib/ReaderWriter/ELF/ArrayOrderPass.cpp
deleted file mode 100644
index b279495d02b..00000000000
--- a/lld/lib/ReaderWriter/ELF/ArrayOrderPass.cpp
+++ /dev/null
@@ -1,56 +0,0 @@
-//===- lib/ReaderWriter/ELF/ArrayOrderPass.cpp ----------------------------===//
-//
-//                             The LLVM Linker
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-
-#include "ArrayOrderPass.h"
-#include <algorithm>
-#include <limits>
-
-namespace lld {
-namespace elf {
-void ArrayOrderPass::perform(std::unique_ptr<MutableFile> &f) {
-  auto definedAtoms = f->definedAtoms();
-
-  // Move sections need to be sorted into the separate continious group.
-  // That reduces a number of sorting elements and simplifies conditions
-  // in the sorting predicate.
-  auto last = std::stable_partition(definedAtoms.begin(), definedAtoms.end(),
-                                    [](const DefinedAtom *atom) {
-    if (atom->sectionChoice() != DefinedAtom::sectionCustomRequired)
-      return false;
-
-    StringRef name = atom->customSectionName();
-    return name.startswith(".init_array") || name.startswith(".fini_array");
-  });
-
-  std::stable_sort(definedAtoms.begin(), last,
-                   [](const DefinedAtom *left, const DefinedAtom *right) {
-    StringRef leftSec = left->customSectionName();
-    StringRef rightSec = right->customSectionName();
-
-    // Drop the front dot from the section name and get
-    // an optional section's number starting after the second dot.
-    StringRef leftNum = leftSec.drop_front().rsplit('.').second;
-    StringRef rightNum = rightSec.drop_front().rsplit('.').second;
-
-    // Sort {.init_array, .fini_array}[.<num>] sections
-    // according to their number. Sections without optional
-    // numer suffix should go last.
-
-    uint32_t leftPriority;
-    uint32_t rightPriority;
-    if (leftNum.getAsInteger(10, leftPriority))
-      leftPriority = std::numeric_limits<uint32_t>::max();
-    if (rightNum.getAsInteger(10, rightPriority))
-      rightPriority = std::numeric_limits<uint32_t>::max();
-
-    return leftPriority < rightPriority;
-  });
-}
-} // end namespace elf
-} // end namespace lld