Commit Graph

183 Commits

Author SHA1 Message Date
Nicola Zaghen d34e60ca85 Rename DEBUG macro to LLVM_DEBUG.
The DEBUG() macro is very generic so it might clash with other projects.
The renaming was done as follows:
- git grep -l 'DEBUG' | xargs sed -i 's/\bDEBUG\s\?(/LLVM_DEBUG(/g'
- git diff -U0 master | ../clang/tools/clang-format/clang-format-diff.py -i -p1 -style LLVM
- Manual change to APInt
- Manually chage DOCS as regex doesn't match it.

In the transition period the DEBUG() macro is still present and aliased
to the LLVM_DEBUG() one.

Differential Revision: https://reviews.llvm.org/D43624

llvm-svn: 332240
2018-05-14 12:53:11 +00:00
Nico Weber 432a38838d IWYU for llvm-config.h in llvm, additions.
See r331124 for how I made a list of files missing the include.
I then ran this Python script:

    for f in open('filelist.txt'):
        f = f.strip()
        fl = open(f).readlines()

        found = False
        for i in xrange(len(fl)):
            p = '#include "llvm/'
            if not fl[i].startswith(p):
                continue
            if fl[i][len(p):] > 'Config':
                fl.insert(i, '#include "llvm/Config/llvm-config.h"\n')
                found = True
                break
        if not found:
            print 'not found', f
        else:
            open(f, 'w').write(''.join(fl))

and then looked through everything with `svn diff | diffstat -l | xargs -n 1000 gvim -p`
and tried to fix include ordering and whatnot.

No intended behavior change.

llvm-svn: 331184
2018-04-30 14:59:11 +00:00
Jonas Devlieghere 9e3e7a99e8 [dsymutil] Upstream emitting of papertrail warnings.
When running dsymutil as part of your build system, it can be desirable
for warnings to be part of the end product, rather than just being
emitted to the output stream. This patch upstreams that functionality.

Differential revision: https://reviews.llvm.org/D44639

llvm-svn: 328965
2018-04-02 10:40:43 +00:00
Rafael Espindola 4b4d85fd4d Style update. NFC.
Rename 3 functions to start with lowercase letters. Don't repeat the
name in the comments.

llvm-svn: 328848
2018-03-29 23:32:54 +00:00
Pavel Labath 8ed6582bb0 Fix msvc compiler error in r327498
msvc reports an "illegal indirection" error here. Attempt to appease it
with a different initialization syntax.

llvm-svn: 327500
2018-03-14 11:31:17 +00:00
Pavel Labath 0dd81bab92 Explicitly initialize dwarf::FormParams in DIEInteger::SizeOf
This could end up inititialized if someone called the function with a
null AsmPrinter. Right now this only happens in DIEHash unit tests,
presumably because it was hard to create an AsmPrinter in the context of
unit tests. This only worked before r327486 because those tests did not
use any dwarf forms whose size actually depended on the dwarf version
(otherwise, they would have crashed due to null dereference).

I fix the uninitialized error, by explicitly initializing FormParams to
an invalid value, which will cause getFixedFormByteSize to return None
if called with a form with version-dependent size. A more principled
solution might be to fix the DIEHash tests to always pass in a valid
AsmPrinter.

llvm-svn: 327498
2018-03-14 11:14:43 +00:00
Pavel Labath 322711f529 DWARF: Unify form size handling code
Summary:
This patch replaces the two switches which are deducing the size of
various forms with a single implementation. I have put the new
implementation into BinaryFormat, to avoid introducing dependencies
between the two independent libraries (DebugInfo and CodeGen) that need
this functionality.

Reviewers: aprantl, JDevlieghere, dblaikie

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D44418

llvm-svn: 327486
2018-03-14 09:39:54 +00:00
Wolfgang Pieb 456b555ffe [DWARF] Generate DWARF v5 string offsets tables along with strx* index forms.
Summary: This is the producer side for DWARF v5 string offsets tables. The reader/consumer
side was committed with r321295. All compile and type units in a module share a 
contribution to the string offsets table. Indirect strings use the strx{1,2,3,4} index forms.

Reviewers: dblaikie, aprantl, JDevliegehere

Differential Revision: https://reviews.llvm.org/D42021

llvm-svn: 323546
2018-01-26 18:52:58 +00:00
Paul Robinson a06f8dcca6 Recommit "[DWARFv5] Dump an MD5 checksum in the line-table header."
Adds missing support for DW_FORM_data16.

Update of r320852/r320886, fixing the unittest again, this time use a
raw char string for the test data.

Differential Revision: https://reviews.llvm.org/D41090

llvm-svn: 321011
2017-12-18 19:08:35 +00:00
Paul Robinson 6d0484f2b6 Revert "Recommit "[DWARFv5] Dump an MD5 checksum in the line-table header.""
This reverts commit 0afef672f63f0e4e91938656bc73424a8c058bfc.
Still failing at runtime on bots.

llvm-svn: 320888
2017-12-15 23:21:52 +00:00
Paul Robinson 5c8f7d7de4 Recommit "[DWARFv5] Dump an MD5 checksum in the line-table header."
Adds missing support for DW_FORM_data16.

Update of r320852, fixing the unittest to use a hand-coded struct
instead of std::array to guarantee data layout.

Differential Revision: https://reviews.llvm.org/D41090

llvm-svn: 320886
2017-12-15 22:57:17 +00:00
Paul Robinson 67ca67d1b2 Revert "[DWARFv5] Dump an MD5 checksum in the line-table header."
Unit test fails on some bots.

llvm-svn: 320857
2017-12-15 20:29:25 +00:00
Paul Robinson 72546fe87b [DWARFv5] Dump an MD5 checksum in the line-table header.
Adds missing support for DW_FORM_data16.

Differential Revision: https://reviews.llvm.org/D41090

llvm-svn: 320852
2017-12-15 19:52:34 +00:00
Aaron Ballman 615eb47035 Reverting r315590; it did not include changes for llvm-tblgen, which is causing link errors for several people.
Error LNK2019 unresolved external symbol "public: void __cdecl `anonymous namespace'::MatchableInfo::dump(void)const " (?dump@MatchableInfo@?A0xf4f1c304@@QEBAXXZ) referenced in function "public: void __cdecl `anonymous namespace'::AsmMatcherEmitter::run(class llvm::raw_ostream &)" (?run@AsmMatcherEmitter@?A0xf4f1c304@@QEAAXAEAVraw_ostream@llvm@@@Z) llvm-tblgen D:\llvm\2017\utils\TableGen\AsmMatcherEmitter.obj 1

llvm-svn: 315854
2017-10-15 14:32:27 +00:00
Don Hinton 3e0199f7eb [dump] Remove NDEBUG from test to enable dump methods [NFC]
Summary:
Add LLVM_FORCE_ENABLE_DUMP cmake option, and use it along with
LLVM_ENABLE_ASSERTIONS to set LLVM_ENABLE_DUMP.

Remove NDEBUG and only use LLVM_ENABLE_DUMP to enable dump methods.

Move definition of LLVM_ENABLE_DUMP from config.h to llvm-config.h so
it'll be picked up by public headers.

Differential Revision: https://reviews.llvm.org/D38406

llvm-svn: 315590
2017-10-12 16:16:06 +00:00
Sam Clegg 705f798bff Mark dump() methods as const. NFC
Add const qualifier to any dump() method where adding one
was trivial.

Differential Revision: https://reviews.llvm.org/D34481

llvm-svn: 305963
2017-06-21 22:19:17 +00:00
David Blaikie 85366acf15 Avoid using relocations for ref_addr in .dwo files
In dwo files the fixed offset can be used - if the dwos are linked into
a dwp, the dwo consumer must use the dwp tables to find out where the
original range of the debug_info was and resolve the "section relative"
value relative to that original range - effectively
avoiding/reimplementing the relocation handling.

llvm-svn: 301072
2017-04-22 07:53:44 +00:00
Paul Robinson 70b34533c2 [DWARF] Versioning for DWARF constants; verify FORMs
Associate the version-when-defined with definitions of standard DWARF
constants.  Identify the "vendor" for DWARF extensions.
Use this information to verify FORMs in .debug_abbrev are defined as
of the DWARF version specified in the associated unit.
Removed two tests that had specified DWARF v1 (which essentially does
not exist).

Differential Revision: http://reviews.llvm.org/D30785

llvm-svn: 300875
2017-04-20 19:16:51 +00:00
Konstantin Zhuravlyov dc77b2e960 Distinguish between code pointer size and DataLayout::getPointerSize() in DWARF info generation
llvm-svn: 300463
2017-04-17 17:41:25 +00:00
Paul Robinson f96e21ad6d [DWARFv5] Update definitions to match published spec.
Some late additions to DWARF v5 were not in Dwarf.def; also one form
was redefined.  Add the new cases to relevant switches in different
parts of LLVM.  Replace DW_FORM_ref_sup with DW_FORM_ref_sup[4,8].

I did not add support for DW_FORM_strx3/addrx3 other that defining the
constants. We don't have any infrastructure to support these.

Differential Revision: http://reviews.llvm.org/D30664

llvm-svn: 297085
2017-03-06 22:20:03 +00:00
Paul Robinson a94f76b18c Remove spurious use of LLVM_FALLTHROUGH (NFC)
llvm-svn: 296713
2017-03-01 23:59:11 +00:00
Victor Leschuk d7bfa40ace [DebugInfo] [DWARFv5] Unique abbrevs for DIEs with different implicit_const values
Take DW_FORM_implicit_const attribute value into account when profiling
DIEAbbrevData.

Currently if we have two similar types with implicit_const attributes and
different values we end up with only one abbrev in .debug_abbrev section.
For example consider two structures: S1 with implicit_const attribute ATTR
and value VAL1 and S2 with implicit_const ATTR and value VAL2.
The .debug_abbrev section will contain only 1 related record:

[N] DW_TAG_structure_type       DW_CHILDREN_yes
        DW_AT_ATTR        DW_FORM_implicit_const  VAL1
        // ....

This is incorrect as struct S2 (with VAL2) will use abbrev record with VAL1.

With this patch we will have two different abbreviations here:

[N] DW_TAG_structure_type       DW_CHILDREN_yes
        DW_AT_ATTR        DW_FORM_implicit_const  VAL1
        // ....

[M] DW_TAG_structure_type       DW_CHILDREN_yes
        DW_AT_ATTR        DW_FORM_implicit_const  VAL2
        // ....

llvm-svn: 296691
2017-03-01 22:13:42 +00:00
Simon Dardis 2e8cdbd795 [DebugInfo] Rename EmitDebugValue to EmitDebugThreadLocal (NFC)
As pointed out by David Blaikie in the post commit review of
r292624, EmitDebugValue should be called EmitDebugThreadLocal.

llvm-svn: 294500
2017-02-08 19:03:46 +00:00
Matthias Braun 8c209aa877 Cleanup dump() functions.
We had various variants of defining dump() functions in LLVM. Normalize
them (this should just consistently implement the things discussed in
http://lists.llvm.org/pipermail/cfe-dev/2014-January/034323.html

For reference:
- Public headers should just declare the dump() method but not use
  LLVM_DUMP_METHOD or #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
- The definition of a dump method should look like this:
  #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
  LLVM_DUMP_METHOD void MyClass::dump() {
    // print stuff to dbgs()...
  }
  #endif

llvm-svn: 293359
2017-01-28 02:02:38 +00:00
Petar Jovanovic dbb39356b4 [mips] Fix debug information for __thread variable
This patch fixes debug information for __thread variable on Mips
using .dtprelword and .dtpreldword directives.

Patch by Aleksandar Beserminji.

Differential Revision: http://reviews.llvm.org/D28770

llvm-svn: 292624
2017-01-20 17:53:30 +00:00
Victor Leschuk cbddae74f5 DebugInfo: support for DW_FORM_implicit_const
Support for DW_FORM_implicit_const DWARFv5 feature.
When this form is used attribute value goes to .debug_abbrev section (as SLEB).
As this form would break any debug tool which doesn't support DWARFv5
it is guarded by dwarf version check. Attempt to use this form with
dwarf version <= 4 is considered a fatal error.

Differential Revision: https://reviews.llvm.org/D28456

llvm-svn: 291599
2017-01-10 21:18:26 +00:00
Keno Fischer f7d84ee6ff Reapply "[CodeGen] Fix invalid DWARF info on Win64"
This reapplies rL289013 (reverted in rL289014) with the fixes identified
in D21731. Should hopefully pass the buildbots this time.

llvm-svn: 290809
2017-01-02 03:00:19 +00:00
Benjamin Kramer eedc4059c3 Plug another leak in the DWARF unittests, DIEInlineStrings are never destroyed.
llvm-svn: 289208
2016-12-09 13:33:41 +00:00
Keno Fischer d4ea4c18f1 Revert "[CodeGen] Fix invalid DWARF info on Win64"
Appears to break on build bots. Reverting pending investigation.

llvm-svn: 289014
2016-12-08 01:56:23 +00:00
Keno Fischer 460218fb7d [CodeGen] Fix invalid DWARF info on Win64
The relocations for `DIEEntry::EmitValue` were wrong for Win64
(emitting FK_Data_4 instead of FK_SecRel_4). This corrects that
oversight so that the DWARF data is correct in Win64 COFF files.

Fixes PR15393.

Patch by Jameson Nash <jameson@juliacomputing.com> based on a patch
by David Majnemer.

Differential Revision: https://reviews.llvm.org/D21731

llvm-svn: 289013
2016-12-08 01:40:21 +00:00
Greg Clayton 3462a420d1 Make a DWARF generator so we can unit test DWARF APIs with gtest.
The only tests we have for the DWARF parser are the tests that use llvm-dwarfdump and expect output from textual dumps.

More DWARF parser modification are coming in the next few weeks and I wanted to add tests that can verify that we can encode and decode all form types, as well as test some other basic DWARF APIs where we ask DIE objects for their children and siblings.

DwarfGenerator.cpp was added in the lib/CodeGen directory. This file contains the code necessary to easily create DWARF for tests:

dwarfgen::Generator DG;
Triple Triple("x86_64--");
bool success = DG.init(Triple, Version);
if (!success)
  return;
dwarfgen::CompileUnit &CU = DG.addCompileUnit();
dwarfgen::DIE CUDie = CU.getUnitDIE();

CUDie.addAttribute(DW_AT_name, DW_FORM_strp, "/tmp/main.c");
CUDie.addAttribute(DW_AT_language, DW_FORM_data2, DW_LANG_C);

dwarfgen::DIE SubprogramDie = CUDie.addChild(DW_TAG_subprogram);
SubprogramDie.addAttribute(DW_AT_name, DW_FORM_strp, "main");
SubprogramDie.addAttribute(DW_AT_low_pc, DW_FORM_addr, 0x1000U);
SubprogramDie.addAttribute(DW_AT_high_pc, DW_FORM_addr, 0x2000U);

dwarfgen::DIE IntDie = CUDie.addChild(DW_TAG_base_type);
IntDie.addAttribute(DW_AT_name, DW_FORM_strp, "int");
IntDie.addAttribute(DW_AT_encoding, DW_FORM_data1, DW_ATE_signed);
IntDie.addAttribute(DW_AT_byte_size, DW_FORM_data1, 4);

dwarfgen::DIE ArgcDie = SubprogramDie.addChild(DW_TAG_formal_parameter);
ArgcDie.addAttribute(DW_AT_name, DW_FORM_strp, "argc");
// ArgcDie.addAttribute(DW_AT_type, DW_FORM_ref4, IntDie);
ArgcDie.addAttribute(DW_AT_type, DW_FORM_ref_addr, IntDie);

StringRef FileBytes = DG.generate();
MemoryBufferRef FileBuffer(FileBytes, "dwarf");
auto Obj = object::ObjectFile::createObjectFile(FileBuffer);
EXPECT_TRUE((bool)Obj);
DWARFContextInMemory DwarfContext(*Obj.get());
This code is backed by the AsmPrinter code that emits DWARF for the actual compiler.

While adding unit tests it was discovered that DIEValue that used DIEEntry as their values had bugs where DW_FORM_ref1, DW_FORM_ref2, DW_FORM_ref8, and DW_FORM_ref_udata forms were not supported. These are all now supported. Added support for DW_FORM_string so we can emit inlined C strings.

Centralized the code to unique abbreviations into a new DIEAbbrevSet class and made both the dwarfgen::Generator and the llvm::DwarfFile classes use the new class.

Fixed comments in the llvm::DIE class so that the Offset is known to be the compile/type unit offset.

DIEInteger now supports more DW_FORM values.

There are also unit tests that cover:

Encoding and decoding all form types and values
Encoding and decoding all reference types (DW_FORM_ref1, DW_FORM_ref2, DW_FORM_ref4, DW_FORM_ref8, DW_FORM_ref_udata, DW_FORM_ref_addr) including cross compile unit references with that go forward one compile unit and backward on compile unit.

Differential Revision: https://reviews.llvm.org/D27326

llvm-svn: 289010
2016-12-08 01:03:48 +00:00
David Blaikie e40caaee99 [debug info] Minor cleanup from D27170/r288399
llvm-svn: 288421
2016-12-01 21:59:09 +00:00
Benjamin Kramer 6a8704c1c0 Fix unused variable warning in Release builds. NFC.
llvm-svn: 288401
2016-12-01 19:10:10 +00:00
Greg Clayton 35630c3357 This change removes the dependency on DwarfDebug that was used for DW_FORM_ref_addr by making a new DIEUnit class in DIE.cpp.
The DIEUnit class represents a compile or type unit and it owns the unit DIE as an instance variable. This allows anyone with a DIE, to get the unit DIE, and then get back to its DIEUnit without adding any new ivars to the DIE class. Why was this needed? The DIE class has an Offset that is always the CU relative DIE offset, not the "offset in debug info section" as was commented in the header file (the comment has been corrected). This is great for performance because most DIE references are compile unit relative and this means most code that accessed the DIE's offset didn't need to make it into a compile unit relative offset because it already was. When we needed to emit a DW_FORM_ref_addr though, we needed to find the absolute offset of the DIE by finding the DIE's compile/type unit. This class did have the absolute debug info/type offset and could be added to the CU relative offset to compute the absolute offset. With this change we can easily get back to a DIE's DIEUnit which will have this needed offset. Prior to this is required having a DwarfDebug and required calling:

DwarfCompileUnit *DwarfDebug::lookupUnit(const DIE *CU) const;
Now we can use the DIEUnit class to do so without needing DwarfDebug. All clients now use DIEUnit objects (the DwarfDebug stack and the DwarfLinker). A follow on patch for the DWARF generator will also take advantage of this.

Differential Revision: https://reviews.llvm.org/D27170

llvm-svn: 288399
2016-12-01 18:56:29 +00:00
Greg Clayton e65439797a Rely on a single DWARF version instead of having two copies
This patch makes AsmPrinter less reliant on DwarfDebug by relying on the DWARF version in the AsmPrinter's MCStreamer's MCContext. This allows us to remove the redundant DWARF version from DwarfDebug. It also lets us change code that used to access the AsmPrinter's DwarfDebug just to get to the DWARF version by changing the DWARF version accessor on AsmPrinter so that it grabs the version from its MCStreamer's MCContext.

Differential Revision: https://reviews.llvm.org/D27032

llvm-svn: 287839
2016-11-23 23:30:37 +00:00
Mehdi Amini 149f6eaed9 Re-commit "Use StringRef in Support/Darf APIs (NFC)"
This reverts commit r283285 and re-commit r283275 with
a fix for format("%s", Str); where Str is a StringRef.

llvm-svn: 283298
2016-10-05 05:59:29 +00:00
Mehdi Amini 2bcac0fac4 Revert "Re-commit "Use StringRef in Support/Darf APIs (NFC)""
One test seems randomly broken: DebugInfo/X86/gnu-public-names.ll

llvm-svn: 283285
2016-10-05 01:04:02 +00:00
Mehdi Amini 32b297a42f Re-commit "Use StringRef in Support/Darf APIs (NFC)"
This reverts commit r283278 and re-commit r283275 with
the update to fix the build on the LLDB side.

llvm-svn: 283281
2016-10-05 00:37:18 +00:00
Mehdi Amini 78b04ae7ac Revert "Use StringRef in Support/Darf APIs (NFC)"
This reverts commit r283275, it broke LLDB Android debug server.

llvm-svn: 283278
2016-10-05 00:21:14 +00:00
Mehdi Amini e0327be584 Use StringRef in Support/Darf APIs (NFC)
llvm-svn: 283275
2016-10-04 23:55:40 +00:00
Justin Bogner cd1d5aaf2e Replace a few more "fall through" comments with LLVM_FALLTHROUGH
Follow up to r278902. I had missed "fall through", with a space.

llvm-svn: 278970
2016-08-17 20:30:52 +00:00
Peter Collingbourne 7c384ccea2 DwarfDebug: emit type units immediately.
Rather than storing type units in a vector and emitting them at the end
of code generation, emit them immediately and destroy them, reclaiming the
memory we were using for their DIEs.

In one benchmark carried out against Chromium's 50 largest (by bitcode
file size) translation units, total peak memory consumption with type units
decreased by median 17%, or by 7% when compared against disabling type units.

Tested using check-{llvm,clang}, the GDB 7.5 test suite (with
'-fdebug-types-section') and by eyeballing llvm-dwarfdump output on those
Chromium translation units with split DWARF both disabled and enabled, and
verifying that the only changes were to addresses and abbreviation ordering.

Differential Revision: http://reviews.llvm.org/D17118

llvm-svn: 260578
2016-02-11 19:57:46 +00:00
Amjad Aboud 8bbce8ad8e Improved macro emission in dwarf.
Changed emitting offset of macinfo entry into compiler unit DIE to use "addSectionLabel" method rather than explicitly calculating size/offset of macro entry.

Differential Revision: http://reviews.llvm.org/D16292

llvm-svn: 259358
2016-02-01 14:09:41 +00:00
Amjad Aboud d7cfb48485 Added support for macro emission in dwarf (supporting DWARF version 4).
Differential Revision: http://reviews.llvm.org/D15495

llvm-svn: 257060
2016-01-07 14:28:20 +00:00
Davide Italiano c304a0ddc1 [DIE] Make DIE.h NDEBUG conditional-free.
Switch dump()/print() method definitions to LLVM_DUMP_METHOD instead.

llvm-svn: 253945
2015-11-24 02:21:43 +00:00
Duncan P. N. Exon Smith c582114d4c AsmPrinter: Split out non-DIE printing from DIE::print(), NFC
Split out a helper `printValues()` for printing `DIEBlock` and `DIELoc`,
instead of relying on `DIE::print()`.  The shared code was actually
fairly small there.  No functionality change intended.

llvm-svn: 243856
2015-08-02 20:46:49 +00:00
Duncan P. N. Exon Smith 1ad5ebc3ed AsmPrinter: Change DIEValueList to a subclass of DIE, NFC
Rewrite `DIEValueList` as a subclass of `DIE`, renaming its API to match
`DIE`'s.  This is preparation for changing `DIEBlock` and `DIELoc` to
stop inheriting from `DIE` and inherit directly from `DIEValueList`.

I thought about leaving this as a has-a relationship (and changing
`DIELoc` and `DIEBlock` to also have-a `DIEValueList`), but that seemed
to require a fair bit more boilerplate and I think it needed more
changes to the `DwarfUnit` API than this will.

No functionality change intended here.

llvm-svn: 243854
2015-08-02 20:42:45 +00:00
Mehdi Amini 1660cab341 Redirect pointerSize query to the TargetMachine in ASMPrinter
Summary:
Because llvm-dsymutil is using ASMPrinter without any MachineFunction
of Module available.

This change is part of a series of commits dedicated to have a single
DataLayout during compilation by using always the one owned by the
module.

Reviewers: echristo

Subscribers: yaron.keren, rafael, llvm-commits

Differential Revision: http://reviews.llvm.org/D11078

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 242384
2015-07-16 05:59:25 +00:00
Duncan P. N. Exon Smith 827200c822 AsmPrinter: Use an intrusively linked list for DIE::Children
Replace the `std::vector<>` for `DIE::Children` with an intrusively
linked list.  This is a strict memory improvement: it requires no
auxiliary storage, and reduces `sizeof(DIE)` by one pointer.  It also
factors out the DIE-related malloc traffic.

This drops llc memory usage from 735 MB down to 718 MB, or ~2.3%.

(I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`;
see r236629 for details.)

llvm-svn: 240736
2015-06-25 23:52:10 +00:00
Duncan P. N. Exon Smith 4fb1f9cda6 AsmPrinter: Convert DIE::Values to a linked list
Change `DIE::Values` to a singly linked list, where each node is
allocated on a `BumpPtrAllocator`.  In order to support `push_back()`,
the list is circular, and points at the tail element instead of the
head.  I abstracted the core list logic out to `IntrusiveBackList` so
that it can be reused for `DIE::Children`, which also cares about
`push_back()`.

This drops llc memory usage from 799 MB down to 735 MB, about 8%.

(I'm looking at `llc` memory usage on `verify-uselistorder.lto.opt.bc`;
see r236629 for details.)

llvm-svn: 240733
2015-06-25 23:46:41 +00:00