[LLVMdev] RFC: ThinLTO Impementation Plan

[Xinliang David Li]

There is no need for emitting the full symtab. I checked the overhead with
a huge internal C++ source. The overhead of symtab + str table compared
with byte code with debug is about 3%.

More importantly, it is also possible to use the symtab also for
index/summary purpose, which makes the space usage completely 'unwasted'.
That gets into the details which will follow when patches are in.

David

On Fri, May 15, 2015 at 5:11 AM, Dave Bozier <seifsta at gmail.com> wrote:

> > Are you sure about the additional I/O? With native symtab, existing
> tools just need to read those, while plugin based approach needs to read
> bit code section to feedback symbols to the tool.
>
> The additional I/O will be quite big if you are going to emit the full
> symbol table. Looking at some of our real world links the symbol table and
> string tables of all the inputs seen by the linker add up to about 50 -
> 100mb.
>
> On Thu, May 14, 2015 at 10:28 PM, Xinliang David Li <xinliangli at gmail.com>
> wrote:
>
>>
>>
>> On Thu, May 14, 2015 at 2:09 PM, Eric Christopher <echristo at gmail.com>
>> wrote:
>>
>>>
>>>
>>> On Thu, May 14, 2015 at 1:35 PM Teresa Johnson <tejohnson at google.com>
>>> wrote:
>>>
>>>> On Thu, May 14, 2015 at 1:18 PM, Eric Christopher <echristo at gmail.com>
>>>> wrote:
>>>> >
>>>> >
>>>> > On Thu, May 14, 2015 at 1:11 PM David Blaikie <dblaikie at gmail.com>
>>>> wrote:
>>>> >>
>>>> >> On Thu, May 14, 2015 at 12:53 PM, Eric Christopher <
>>>> echristo at gmail.com>
>>>> >> wrote:
>>>> >>>
>>>> >>>
>>>> >>>
>>>> >>> On Thu, May 14, 2015 at 11:34 AM Daniel Berlin <dberlin at dberlin.org
>>>> >
>>>> >>> wrote:
>>>> >>>>
>>>> >>>> On Thu, May 14, 2015 at 11:14 AM, Eric Christopher <
>>>> echristo at gmail.com>
>>>> >>>> wrote:
>>>> >>>> > I'm not sure this is a particularly great assumption to make.
>>>> >>>>
>>>> >>>> Which part?
>>>> >>>
>>>> >>>
>>>> >>> The binutils part :)
>>>> >>>
>>>> >>>>
>>>> >>>>
>>>> >>>> >  We have to
>>>> >>>> > support a lot of different build systems and tools and
>>>> concentrating
>>>> >>>> > on
>>>> >>>> > something that just binutils uses isn't particularly friendly
>>>> here.
>>>> >>>> I think you may have misunderstood
>>>> >>>> His point was exactly that they want to be transparent to *all of*
>>>> these
>>>> >>>> tools.
>>>> >>>> You are saying "we should be friendly to everyone". He is saying
>>>> the
>>>> >>>> same thing.
>>>> >>>> We should be friendly to everyone. The friendly way to do this is
>>>> to
>>>> >>>> not require all of these tools build plugins to handle bitcode.
>>>> >>>>
>>>> >>>> Hence, elf-wrapped bitcode.
>>>> >>>
>>>> >>>
>>>> >>> Oh, I understood. I just don't know that I agree. To do anything
>>>> with the
>>>> >>> tools will require some knowledge of bitcode anyhow or need the
>>>> plugin. I'm
>>>> >>> saying that as a baseline start we should look at how to do this
>>>> using the
>>>> >>> tools we've got rather than wrapping things for no real gain.
>>>> >>
>>>> >>
>>>> >> That doesn't seem strictly true - the ar situation (which I'm lead to
>>>> >> believe is in use in our build system & others, one would assume).
>>>> With the
>>>> >> symbol table included as proposed, ar can be used without any
>>>> knowledge of
>>>> >> the bitcode or need for a plugin.
>>>> >>
>>>> >
>>>> > For some bits, sure. Optimizing for ar seems a bit silly, why not 'ld
>>>> -r'?
>>>>
>>>> But as mentioned, ld -r can work on native object wrapped bitcode
>>>> without a plugin as well.
>>>>
>>>>
>>> How? It's not like any partial linking is going to go on inside the
>>> bitcode if the linker doesn't understand bitcode.
>>>
>>
>> What do we want plugin to do anything here?  We just need the linker to
>> concatenate the bitcode sections and produce a combined bitcode file.
>>
>>
>>>
>>>
>>>> > Agreed. The ar situation is interesting because one thing we
>>>> discussed after
>>>> > you wandered off was just adding a ToC section to bitcode as it is
>>>> and then
>>>> > having the tools handle that. Would seem to accomplish at least the
>>>> goals as
>>>> > I've seen them up to this point without worrying too much.
>>>>
>>>> The ToC section is a way we can encode the function index/summary into
>>>> bitcode, but won't help integrate with existing tools. The main issue
>>>> we are trying to solve is integrating transparently with existing
>>>> binutils tools in use in our build system and probably elsewhere.
>>>>
>>>>
>>> Right. I'm not entirely sure what use we're going to see in the existing
>>> tools that we want to encompass here. There's some of it for convenience
>>> (i.e. nm etc for developers), but they can use a tool that understands
>>> bitcode and we can make the existing llvm tools suffice for these needs.
>>>
>>> I think the way of looking at this is that we can:
>>>
>>> a) go with wrapping things in native object formats, this means
>>>  - some tools continue to work at the cost of additional I/O and space
>>> at compile/link time
>>>
>>
>> Are you sure about the additional I/O? With native symtab, existing tools
>> just need to read those, while plugin based approach needs to read bit code
>> section to feedback symbols to the tool.
>>
>>
>>>  - we still have to update some tools to work at all
>>>
>>
>> If any, it will be minimal.
>>
>>
>>>
>>> b) we extend those tools/our own tools and have them be drop in
>>> replacements to the existing tools. They'll understand the bitcode format
>>> natively, they'll be smaller, and we'll be able to push the state of the
>>> art in tooling/analysis a bit more in the future without having to rework
>>> thin lto.
>>>
>>> It's basically a set of trade-offs and for llvm we've historically gone
>>> the b direction.
>>>
>>>
>> I am fine making llvm tools work with it, but we should not require/force
>> user using them. I think this is an orthogonal feature.
>>
>> David
>>
>>
>>
>>
>>> >
>>>> > At any rate, I think this aspect of the proposal needs a bit of
>>>> discussion
>>>> > and some mapping out of the pros and cons here.
>>>>
>>>> Sure, we can continue to discuss and I will try to lay out the
>>>> pros/cons.
>>>>
>>>
>>> Excellent.
>>>
>>> -eric
>>>
>>>
>>>>
>>>> Teresa
>>>>
>>>> >
>>>> > -eric
>>>> >
>>>> >>>
>>>> >>> I've talked to Teresa a bit offline and we're going to talk more
>>>> later
>>>> >>> (and discuss on the list), but there are some discussions about how
>>>> to make
>>>> >>> this work either with just bitcode/llvm tools and so not requiring
>>>> >>> integration on all platforms. The latter is what I consider as
>>>> particularly
>>>> >>> friendly :)
>>>> >>>
>>>> >>> -eric
>>>> >>>
>>>> >>>>
>>>> >>>>
>>>> >>>>
>>>> >>>> > I also
>>>> >>>> > can't imagine how it's necessary for any of the lto aspects as
>>>> >>>> > currently
>>>> >>>> > written in the proposal.
>>>> >>>> >
>>>> >>>> > -eric
>>>> >>>> >
>>>> >>>> > On Thu, May 14, 2015 at 9:26 AM Xinliang David Li
>>>> >>>> > <xinliangli at gmail.com>
>>>> >>>> > wrote:
>>>> >>>> >>
>>>> >>>> >> The design objective is to make thinLTO mostly transparent to
>>>> binutil
>>>> >>>> >> tools to enable easy integration with any build system in the
>>>> wild.
>>>> >>>> >> 'Pass-through' mode with 'ld -r' instead of the partial LTO
>>>> mode is
>>>> >>>> >> another
>>>> >>>> >> reason.
>>>> >>>> >>
>>>> >>>> >> David
>>>> >>>> >>
>>>> >>>> >> On Thu, May 14, 2015 at 7:30 AM, Teresa Johnson
>>>> >>>> >> <tejohnson at google.com>
>>>> >>>> >> wrote:
>>>> >>>> >>>
>>>> >>>> >>> On Thu, May 14, 2015 at 7:22 AM, Eric Christopher
>>>> >>>> >>> <echristo at gmail.com>
>>>> >>>> >>> wrote:
>>>> >>>> >>> > So, what Alex is saying is that we have these tools as well
>>>> and
>>>> >>>> >>> > they
>>>> >>>> >>> > understand bitcode just fine, as well as every object format
>>>> - not
>>>> >>>> >>> > just
>>>> >>>> >>> > ELF.
>>>> >>>> >>> > :)
>>>> >>>> >>>
>>>> >>>> >>> Right, there are also LLVM specific versions (llvm-ar,
>>>> llvm-nm) that
>>>> >>>> >>> handle bitcode similarly to the way the standard tool + plugin
>>>> does.
>>>> >>>> >>> But the goal we are trying to achieve is to allow the standard
>>>> >>>> >>> system
>>>> >>>> >>> versions of the tools to handle these files without requiring a
>>>> >>>> >>> plugin. I know the LLVM tool handles other object formats, but
>>>> I'm
>>>> >>>> >>> not
>>>> >>>> >>> sure how that helps here? We're not planning to replace those
>>>> tools,
>>>> >>>> >>> just allow the standard system versions to handle the
>>>> intermediate
>>>> >>>> >>> objects produced by ThinLTO.
>>>> >>>> >>>
>>>> >>>> >>> Thanks,
>>>> >>>> >>> Teresa
>>>> >>>> >>>
>>>> >>>> >>> >
>>>> >>>> >>> > -eric
>>>> >>>> >>> >
>>>> >>>> >>> >
>>>> >>>> >>> > On Thu, May 14, 2015, 6:55 AM Teresa Johnson
>>>> >>>> >>> > <tejohnson at google.com>
>>>> >>>> >>> > wrote:
>>>> >>>> >>> >>
>>>> >>>> >>> >> On Wed, May 13, 2015 at 11:23 PM, Xinliang David Li
>>>> >>>> >>> >> <xinliangli at gmail.com> wrote:
>>>> >>>> >>> >> >
>>>> >>>> >>> >> >
>>>> >>>> >>> >> > On Wed, May 13, 2015 at 10:46 PM, Alex Rosenberg
>>>> >>>> >>> >> > <alexr at leftfield.org>
>>>> >>>> >>> >> > wrote:
>>>> >>>> >>> >> >>
>>>> >>>> >>> >> >> "ELF-wrapped bitcode" seems potentially controversial to
>>>> me.
>>>> >>>> >>> >> >>
>>>> >>>> >>> >> >> What about ar, nm, and various ld implementations adds
>>>> this
>>>> >>>> >>> >> >> requirement?
>>>> >>>> >>> >> >> What about the LLVM implementations of these tools is
>>>> lacking?
>>>> >>>> >>> >> >
>>>> >>>> >>> >> >
>>>> >>>> >>> >> > Sorry I can not parse your questions properly. Can you
>>>> make it
>>>> >>>> >>> >> > clearer?
>>>> >>>> >>> >>
>>>> >>>> >>> >> Alex is asking what the issue is with ar, nm, ld -r and
>>>> regular
>>>> >>>> >>> >> bitcode that makes using elf-wrapped bitcode easier.
>>>> >>>> >>> >>
>>>> >>>> >>> >> The issue is that generally you need to provide a plugin to
>>>> these
>>>> >>>> >>> >> tools in order for them to understand and handle bitcode
>>>> files.
>>>> >>>> >>> >> We'd
>>>> >>>> >>> >> like standard tools to work without requiring a plugin as
>>>> much as
>>>> >>>> >>> >> possible. And in some cases we want them to be handled
>>>> different
>>>> >>>> >>> >> than
>>>> >>>> >>> >> the way bitcode files are handled with the plugin.
>>>> >>>> >>> >>
>>>> >>>> >>> >> nm: Without a plugin, normal bitcode files are inscrutable.
>>>> When
>>>> >>>> >>> >> provided the gold plugin it can emit the symbols.
>>>> >>>> >>> >>
>>>> >>>> >>> >> ar: Without a plugin, it will create an archive of bitcode
>>>> files,
>>>> >>>> >>> >> but
>>>> >>>> >>> >> without an index, so it can't be handled by the linker even
>>>> with
>>>> >>>> >>> >> a
>>>> >>>> >>> >> plugin on an -flto link. When ar is provided the gold
>>>> plugin it
>>>> >>>> >>> >> does
>>>> >>>> >>> >> create an index, so the linker + gold plugin handle it
>>>> >>>> >>> >> appropriately
>>>> >>>> >>> >> on an -flto link.
>>>> >>>> >>> >>
>>>> >>>> >>> >> ld -r: Without a plugin, fails when provided bitcode
>>>> inputs. When
>>>> >>>> >>> >> provided the gold plugin, it handles them but compiles them
>>>> all
>>>> >>>> >>> >> the
>>>> >>>> >>> >> way through to ELF executable instructions via a partial LTO
>>>> >>>> >>> >> link.
>>>> >>>> >>> >> This is where we would like to differ in behavior (while
>>>> also not
>>>> >>>> >>> >> requiring a plugin) with ELF-wrapped bitcode: we would like
>>>> the
>>>> >>>> >>> >> ld -r
>>>> >>>> >>> >> output file to still contain ELF-wrapped bitcode, delaying
>>>> the
>>>> >>>> >>> >> LTO
>>>> >>>> >>> >> until the full link step.
>>>> >>>> >>> >>
>>>> >>>> >>> >> Let me know if that helps address your concerns.
>>>> >>>> >>> >>
>>>> >>>> >>> >> Thanks,
>>>> >>>> >>> >> Teresa
>>>> >>>> >>> >>
>>>> >>>> >>> >> >
>>>> >>>> >>> >> > David
>>>> >>>> >>> >> >
>>>> >>>> >>> >> >>
>>>> >>>> >>> >> >>
>>>> >>>> >>> >> >> Alex
>>>> >>>> >>> >> >>
>>>> >>>> >>> >> >> > On May 13, 2015, at 7:44 PM, Teresa Johnson
>>>> >>>> >>> >> >> > <tejohnson at google.com>
>>>> >>>> >>> >> >> > wrote:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > I've included below an RFC for implementing ThinLTO in
>>>> LLVM,
>>>> >>>> >>> >> >> > looking
>>>> >>>> >>> >> >> > forward to feedback and questions.
>>>> >>>> >>> >> >> > Thanks!
>>>> >>>> >>> >> >> > Teresa
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > RFC to discuss plans for implementing ThinLTO upstream.
>>>> >>>> >>> >> >> > Background
>>>> >>>> >>> >> >> > can
>>>> >>>> >>> >> >> > be found in slides from EuroLLVM 2015:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> https://drive.google.com/open?id=0B036uwnWM6RWWER1ZEl5SUNENjQ&authuser=0
>>>> )
>>>> >>>> >>> >> >> > As described in the talk, we have a prototype
>>>> >>>> >>> >> >> > implementation, and
>>>> >>>> >>> >> >> > would like to start staging patches upstream. This RFC
>>>> >>>> >>> >> >> > describes
>>>> >>>> >>> >> >> > a
>>>> >>>> >>> >> >> > breakdown of the major pieces. We would like to commit
>>>> >>>> >>> >> >> > upstream
>>>> >>>> >>> >> >> > gradually in several stages, with all functionality
>>>> off by
>>>> >>>> >>> >> >> > default.
>>>> >>>> >>> >> >> > The core ThinLTO importing support and tuning will
>>>> require
>>>> >>>> >>> >> >> > frequent
>>>> >>>> >>> >> >> > change and iteration during testing and tuning, and
>>>> for that
>>>> >>>> >>> >> >> > part
>>>> >>>> >>> >> >> > we
>>>> >>>> >>> >> >> > would like to commit rapidly (off by default). See the
>>>> >>>> >>> >> >> > proposed
>>>> >>>> >>> >> >> > staged
>>>> >>>> >>> >> >> > implementation described in the Implementation Plan
>>>> section.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > ThinLTO Overview
>>>> >>>> >>> >> >> > ==============
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > See the talk slides linked above for more details. The
>>>> >>>> >>> >> >> > following
>>>> >>>> >>> >> >> > is a
>>>> >>>> >>> >> >> > high-level overview of the motivation.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Cross Module Optimization (CMO) is an effective means
>>>> for
>>>> >>>> >>> >> >> > improving
>>>> >>>> >>> >> >> > runtime performance, by extending the scope of
>>>> optimizations
>>>> >>>> >>> >> >> > across
>>>> >>>> >>> >> >> > source module boundaries. Without CMO, the compiler is
>>>> >>>> >>> >> >> > limited to
>>>> >>>> >>> >> >> > optimizing within the scope of single source modules.
>>>> Two
>>>> >>>> >>> >> >> > solutions
>>>> >>>> >>> >> >> > for enabling CMO are Link-Time Optimization (LTO),
>>>> which is
>>>> >>>> >>> >> >> > currently
>>>> >>>> >>> >> >> > supported in LLVM and GCC, and
>>>> Lightweight-Interprocedural
>>>> >>>> >>> >> >> > Optimization (LIPO). However, each of these solutions
>>>> has
>>>> >>>> >>> >> >> > limitations
>>>> >>>> >>> >> >> > that prevent it from being enabled by default. ThinLTO
>>>> is a
>>>> >>>> >>> >> >> > new
>>>> >>>> >>> >> >> > approach that attempts to address these limitations,
>>>> with a
>>>> >>>> >>> >> >> > goal
>>>> >>>> >>> >> >> > of
>>>> >>>> >>> >> >> > being enabled more broadly. ThinLTO is designed with
>>>> many of
>>>> >>>> >>> >> >> > the
>>>> >>>> >>> >> >> > same
>>>> >>>> >>> >> >> > principals as LIPO, and therefore its advantages,
>>>> without
>>>> >>>> >>> >> >> > any of
>>>> >>>> >>> >> >> > its
>>>> >>>> >>> >> >> > inherent weakness. Unlike in LIPO where the module
>>>> group
>>>> >>>> >>> >> >> > decision
>>>> >>>> >>> >> >> > is
>>>> >>>> >>> >> >> > made at profile training runtime, ThinLTO makes the
>>>> decision
>>>> >>>> >>> >> >> > at
>>>> >>>> >>> >> >> > compile time, but in a lazy mode that facilitates large
>>>> >>>> >>> >> >> > scale
>>>> >>>> >>> >> >> > parallelism. The serial linker plugin phase is
>>>> designed to
>>>> >>>> >>> >> >> > be
>>>> >>>> >>> >> >> > razor
>>>> >>>> >>> >> >> > thin and blazingly fast. By default this step only does
>>>> >>>> >>> >> >> > minimal
>>>> >>>> >>> >> >> > preparation work to enable the parallel lazy importing
>>>> >>>> >>> >> >> > performed
>>>> >>>> >>> >> >> > later. ThinLTO aims to be scalable like a regular O2
>>>> build,
>>>> >>>> >>> >> >> > enabling
>>>> >>>> >>> >> >> > CMO on machines without large memory configurations,
>>>> while
>>>> >>>> >>> >> >> > also
>>>> >>>> >>> >> >> > integrating well with distributed build systems.
>>>> Results
>>>> >>>> >>> >> >> > from
>>>> >>>> >>> >> >> > early
>>>> >>>> >>> >> >> > prototyping on SPEC cpu2006 C++ benchmarks are in line
>>>> with
>>>> >>>> >>> >> >> > expectations that ThinLTO can scale like O2 while
>>>> enabling
>>>> >>>> >>> >> >> > much
>>>> >>>> >>> >> >> > of
>>>> >>>> >>> >> >> > the
>>>> >>>> >>> >> >> > CMO performed during a full LTO build.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > A ThinLTO build is divided into 3 phases, which are
>>>> referred
>>>> >>>> >>> >> >> > to
>>>> >>>> >>> >> >> > in
>>>> >>>> >>> >> >> > the
>>>> >>>> >>> >> >> > following implementation plan:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > phase-1: IR and Function Summary Generation (-c
>>>> compile)
>>>> >>>> >>> >> >> > phase-2: Thin Linker Plugin Layer (thin archive linker
>>>> step)
>>>> >>>> >>> >> >> > phase-3: Parallel Backend with Demand-Driven Importing
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Implementation Plan
>>>> >>>> >>> >> >> > ================
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > This section gives a high-level breakdown of the
>>>> ThinLTO
>>>> >>>> >>> >> >> > support
>>>> >>>> >>> >> >> > that
>>>> >>>> >>> >> >> > will be added, in roughly the order that the patches
>>>> would
>>>> >>>> >>> >> >> > be
>>>> >>>> >>> >> >> > staged.
>>>> >>>> >>> >> >> > The patches are divided into three stages. The first
>>>> stage
>>>> >>>> >>> >> >> > contains a
>>>> >>>> >>> >> >> > minimal amount of preparation work that is not
>>>> >>>> >>> >> >> > ThinLTO-specific.
>>>> >>>> >>> >> >> > The
>>>> >>>> >>> >> >> > second stage contains most of the infrastructure for
>>>> >>>> >>> >> >> > ThinLTO,
>>>> >>>> >>> >> >> > which
>>>> >>>> >>> >> >> > will be off by default. The third stage includes
>>>> >>>> >>> >> >> > enhancements/improvements/tunings that can be performed
>>>> >>>> >>> >> >> > after the
>>>> >>>> >>> >> >> > main
>>>> >>>> >>> >> >> > ThinLTO infrastructure is in.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > The second and third implementation stages will
>>>> initially be
>>>> >>>> >>> >> >> > very
>>>> >>>> >>> >> >> > volatile, requiring a lot of iterations and tuning with
>>>> >>>> >>> >> >> > large
>>>> >>>> >>> >> >> > apps to
>>>> >>>> >>> >> >> > get stabilized. Therefore it will be important to do
>>>> fast
>>>> >>>> >>> >> >> > commits
>>>> >>>> >>> >> >> > for
>>>> >>>> >>> >> >> > these implementation stages.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > 1. Stage 1: Preparation
>>>> >>>> >>> >> >> > -------------------------------
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > The first planned sets of patches are enablers for
>>>> ThinLTO
>>>> >>>> >>> >> >> > work:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > a. LTO directory structure:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Restructure the LTO directory to remove circular
>>>> dependence
>>>> >>>> >>> >> >> > when
>>>> >>>> >>> >> >> > ThinLTO pass added. Because ThinLTO is being
>>>> implemented as
>>>> >>>> >>> >> >> > a SCC
>>>> >>>> >>> >> >> > pass
>>>> >>>> >>> >> >> > within Transforms/IPO, and leverages the LTOModule
>>>> class for
>>>> >>>> >>> >> >> > linking
>>>> >>>> >>> >> >> > in functions from modules, IPO then requires the LTO
>>>> >>>> >>> >> >> > library.
>>>> >>>> >>> >> >> > This
>>>> >>>> >>> >> >> > creates a circular dependence between LTO and IPO. To
>>>> break
>>>> >>>> >>> >> >> > that,
>>>> >>>> >>> >> >> > we
>>>> >>>> >>> >> >> > need to split the lib/LTO directory/library into
>>>> >>>> >>> >> >> > lib/LTO/CodeGen
>>>> >>>> >>> >> >> > and
>>>> >>>> >>> >> >> > lib/LTO/Module, containing LTOCodeGenerator and
>>>> LTOModule,
>>>> >>>> >>> >> >> > respectively. Only LTOCodeGenerator has a dependence
>>>> on IPO,
>>>> >>>> >>> >> >> > removing
>>>> >>>> >>> >> >> > the circular dependence.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > b. ELF wrapper generation support:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Implement ELF wrapped bitcode writer. In order to more
>>>> >>>> >>> >> >> > easily
>>>> >>>> >>> >> >> > interact
>>>> >>>> >>> >> >> > with tools such as $AR, $NM, and “$LD -r” we plan to
>>>> emit
>>>> >>>> >>> >> >> > the
>>>> >>>> >>> >> >> > phase-1
>>>> >>>> >>> >> >> > bitcode wrapped in ELF via the .llvmbc section, along
>>>> with a
>>>> >>>> >>> >> >> > symbol
>>>> >>>> >>> >> >> > table. The goal is both to interact with these tools
>>>> without
>>>> >>>> >>> >> >> > requiring
>>>> >>>> >>> >> >> > a plugin, and also to avoid doing partial LTO/ThinLTO
>>>> across
>>>> >>>> >>> >> >> > files
>>>> >>>> >>> >> >> > linked with “$LD -r” (i.e. the resulting object file
>>>> should
>>>> >>>> >>> >> >> > still
>>>> >>>> >>> >> >> > contain ELF-wrapped bitcode to enable ThinLTO at the
>>>> full
>>>> >>>> >>> >> >> > link
>>>> >>>> >>> >> >> > step).
>>>> >>>> >>> >> >> > I will send a separate design document for these
>>>> changes,
>>>> >>>> >>> >> >> > but the
>>>> >>>> >>> >> >> > following is a high-level overview.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Support was added to LLVM for reading ELF-wrapped
>>>> bitcode
>>>> >>>> >>> >> >> > (http://reviews.llvm.org/rL218078), but there does
>>>> not yet
>>>> >>>> >>> >> >> > exist
>>>> >>>> >>> >> >> > support in LLVM/Clang for emitting bitcode wrapped in
>>>> ELF. I
>>>> >>>> >>> >> >> > plan
>>>> >>>> >>> >> >> > to
>>>> >>>> >>> >> >> > add support for optionally generating bitcode in an
>>>> ELF file
>>>> >>>> >>> >> >> > containing a single .llvmbc section holding the
>>>> bitcode.
>>>> >>>> >>> >> >> > Specifically,
>>>> >>>> >>> >> >> > the patch would add new options “emit-llvm-bc-elf”
>>>> (object
>>>> >>>> >>> >> >> > file)
>>>> >>>> >>> >> >> > and
>>>> >>>> >>> >> >> > corresponding “emit-llvm-elf” (textual assembly code
>>>> >>>> >>> >> >> > equivalent).
>>>> >>>> >>> >> >> > Eventually these would be automatically triggered under
>>>> >>>> >>> >> >> > “-fthinlto
>>>> >>>> >>> >> >> > -c”
>>>> >>>> >>> >> >> > and “-fthinlto -S”, respectively.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Additionally, a symbol table will be generated in the
>>>> ELF
>>>> >>>> >>> >> >> > file,
>>>> >>>> >>> >> >> > holding the function symbols within the bitcode. This
>>>> >>>> >>> >> >> > facilitates
>>>> >>>> >>> >> >> > handling archives of the ELF-wrapped bitcode created
>>>> with
>>>> >>>> >>> >> >> > $AR,
>>>> >>>> >>> >> >> > since
>>>> >>>> >>> >> >> > the archive will have a symbol table as well. The
>>>> archive
>>>> >>>> >>> >> >> > symbol
>>>> >>>> >>> >> >> > table
>>>> >>>> >>> >> >> > enables gold to extract and pass to the plugin the
>>>> >>>> >>> >> >> > constituent
>>>> >>>> >>> >> >> > ELF-wrapped bitcode files. To support the concatenated
>>>> >>>> >>> >> >> > llvmbc
>>>> >>>> >>> >> >> > section
>>>> >>>> >>> >> >> > generated by “$LD -r”, some handling needs to be added
>>>> to
>>>> >>>> >>> >> >> > gold
>>>> >>>> >>> >> >> > and to
>>>> >>>> >>> >> >> > the backend driver to process each original module’s
>>>> >>>> >>> >> >> > bitcode.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > The function index/summary will later be added as a
>>>> special
>>>> >>>> >>> >> >> > ELF
>>>> >>>> >>> >> >> > section alongside the .llvmbc sections.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > 2. Stage 2: ThinLTO Infrastructure
>>>> >>>> >>> >> >> > ----------------------------------------------
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > The next set of patches adds the base implementation
>>>> of the
>>>> >>>> >>> >> >> > ThinLTO
>>>> >>>> >>> >> >> > infrastructure, specifically those required to make
>>>> ThinLTO
>>>> >>>> >>> >> >> > functional
>>>> >>>> >>> >> >> > and generate correct but not necessarily
>>>> high-performing
>>>> >>>> >>> >> >> > binaries. It
>>>> >>>> >>> >> >> > also does not include support to make debug support
>>>> under -g
>>>> >>>> >>> >> >> > efficient
>>>> >>>> >>> >> >> > with ThinLTO.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > a. Clang/LLVM/gold linker options:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > An early set of clang/llvm patches is needed to provide
>>>> >>>> >>> >> >> > options
>>>> >>>> >>> >> >> > to
>>>> >>>> >>> >> >> > enable ThinLTO (off by default), so that the rest of
>>>> the
>>>> >>>> >>> >> >> > implementation can be disabled by default as it is
>>>> added.
>>>> >>>> >>> >> >> > Specifically, clang options -fthinlto (used instead of
>>>> >>>> >>> >> >> > -flto)
>>>> >>>> >>> >> >> > will
>>>> >>>> >>> >> >> > cause clang to invoke the phase-1 emission of LLVM
>>>> bitcode
>>>> >>>> >>> >> >> > and
>>>> >>>> >>> >> >> > function summary/index on a compile step, and pass the
>>>> >>>> >>> >> >> > appropriate
>>>> >>>> >>> >> >> > option to the gold plugin on a link step. The -thinlto
>>>> >>>> >>> >> >> > option
>>>> >>>> >>> >> >> > will be
>>>> >>>> >>> >> >> > added to the gold plugin and llvm-lto tool to launch
>>>> the
>>>> >>>> >>> >> >> > phase-2
>>>> >>>> >>> >> >> > thin
>>>> >>>> >>> >> >> > archive step. The -thinlto option will also be added
>>>> to the
>>>> >>>> >>> >> >> > ‘opt’
>>>> >>>> >>> >> >> > tool
>>>> >>>> >>> >> >> > to invoke it as a phase-3 parallel backend instance.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > b. Thin-archive linking support in Gold plugin and
>>>> llvm-lto:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Under the new plugin option (see above), the plugin
>>>> needs to
>>>> >>>> >>> >> >> > perform
>>>> >>>> >>> >> >> > the phase-2 (thin archive) link which simply emits a
>>>> >>>> >>> >> >> > combined
>>>> >>>> >>> >> >> > function
>>>> >>>> >>> >> >> > map from the linked modules, without actually
>>>> performing the
>>>> >>>> >>> >> >> > normal
>>>> >>>> >>> >> >> > link. Corresponding support should be added to the
>>>> >>>> >>> >> >> > standalone
>>>> >>>> >>> >> >> > llvm-lto
>>>> >>>> >>> >> >> > tool to enable testing/debugging without involving the
>>>> >>>> >>> >> >> > linker and
>>>> >>>> >>> >> >> > plugin.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > c. ThinLTO backend support:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Support for invoking a phase-3 backend invocation
>>>> (including
>>>> >>>> >>> >> >> > importing) on a module should be added to the ‘opt’
>>>> tool
>>>> >>>> >>> >> >> > under
>>>> >>>> >>> >> >> > the
>>>> >>>> >>> >> >> > new
>>>> >>>> >>> >> >> > option. The main change under the option is to
>>>> instantiate a
>>>> >>>> >>> >> >> > Linker
>>>> >>>> >>> >> >> > object used to manage the process of linking imported
>>>> >>>> >>> >> >> > functions
>>>> >>>> >>> >> >> > into
>>>> >>>> >>> >> >> > the module, efficient read of the combined function
>>>> map, and
>>>> >>>> >>> >> >> > enable
>>>> >>>> >>> >> >> > the ThinLTO import pass.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > d. Function index/summary support:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > This includes infrastructure for writing and reading
>>>> the
>>>> >>>> >>> >> >> > function
>>>> >>>> >>> >> >> > index/summary section. As noted earlier this will be
>>>> encoded
>>>> >>>> >>> >> >> > in a
>>>> >>>> >>> >> >> > special ELF section within the module, alongside the
>>>> .llvmbc
>>>> >>>> >>> >> >> > section
>>>> >>>> >>> >> >> > containing the bitcode. The thin archive generated by
>>>> >>>> >>> >> >> > phase-2 of
>>>> >>>> >>> >> >> > ThinLTO simply contains all of the function
>>>> index/summary
>>>> >>>> >>> >> >> > sections
>>>> >>>> >>> >> >> > across the linked modules, organized for efficient
>>>> function
>>>> >>>> >>> >> >> > lookup.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Each function available for importing from the module
>>>> >>>> >>> >> >> > contains an
>>>> >>>> >>> >> >> > entry in the module’s function index/summary section
>>>> and in
>>>> >>>> >>> >> >> > the
>>>> >>>> >>> >> >> > resulting combined function map. Each function entry
>>>> >>>> >>> >> >> > contains
>>>> >>>> >>> >> >> > that
>>>> >>>> >>> >> >> > function’s offset within the bitcode file, used to
>>>> >>>> >>> >> >> > efficiently
>>>> >>>> >>> >> >> > locate
>>>> >>>> >>> >> >> > and quickly import just that function. The entry also
>>>> >>>> >>> >> >> > contains
>>>> >>>> >>> >> >> > summary
>>>> >>>> >>> >> >> > information (e.g. basic information determined during
>>>> >>>> >>> >> >> > parsing
>>>> >>>> >>> >> >> > such as
>>>> >>>> >>> >> >> > the number of instructions in the function), that will
>>>> be
>>>> >>>> >>> >> >> > used to
>>>> >>>> >>> >> >> > help
>>>> >>>> >>> >> >> > guide later import decisions. Because the contents of
>>>> this
>>>> >>>> >>> >> >> > section
>>>> >>>> >>> >> >> > will change frequently during ThinLTO tuning, it
>>>> should also
>>>> >>>> >>> >> >> > be
>>>> >>>> >>> >> >> > marked
>>>> >>>> >>> >> >> > with a version id for backwards compatibility or
>>>> version
>>>> >>>> >>> >> >> > checking.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > e. ThinLTO importing support:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Support for the mechanics of importing functions from
>>>> other
>>>> >>>> >>> >> >> > modules,
>>>> >>>> >>> >> >> > which can go in gradually as a set of patches since it
>>>> will
>>>> >>>> >>> >> >> > be
>>>> >>>> >>> >> >> > off by
>>>> >>>> >>> >> >> > default. Separate patches can include:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > - BitcodeReader changes to use function index to
>>>> >>>> >>> >> >> > import/deserialize
>>>> >>>> >>> >> >> > single function of interest (small changes, leverages
>>>> >>>> >>> >> >> > existing
>>>> >>>> >>> >> >> > lazy
>>>> >>>> >>> >> >> > streamer support).
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > - Minor LTOModule changes to pass the ThinLTO function
>>>> to
>>>> >>>> >>> >> >> > import
>>>> >>>> >>> >> >> > and
>>>> >>>> >>> >> >> > its index into bitcode reader.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > - Marking of imported functions (for use in
>>>> ThinLTO-specific
>>>> >>>> >>> >> >> > symbol
>>>> >>>> >>> >> >> > linking and global DCE, for example). This can be
>>>> in-memory
>>>> >>>> >>> >> >> > initially,
>>>> >>>> >>> >> >> > but IR support may be required in order to support
>>>> streaming
>>>> >>>> >>> >> >> > bitcode
>>>> >>>> >>> >> >> > out and back in again after importing.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > - ModuleLinker changes to do ThinLTO-specific symbol
>>>> linking
>>>> >>>> >>> >> >> > and
>>>> >>>> >>> >> >> > static promotion when necessary. The linkage type of
>>>> >>>> >>> >> >> > imported
>>>> >>>> >>> >> >> > functions changes to AvailableExternallyLinkage, for
>>>> >>>> >>> >> >> > example.
>>>> >>>> >>> >> >> > Statics
>>>> >>>> >>> >> >> > must be promoted in certain cases, and renamed in
>>>> consistent
>>>> >>>> >>> >> >> > ways.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > - GlobalDCE changes to support removing imported
>>>> functions
>>>> >>>> >>> >> >> > that
>>>> >>>> >>> >> >> > were
>>>> >>>> >>> >> >> > not inlined (very small changes to existing pass
>>>> logic).
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > f. ThinLTO Import Driver SCC pass:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Adds Transforms/IPO/ThinLTO.cpp with framework for
>>>> doing
>>>> >>>> >>> >> >> > ThinLTO
>>>> >>>> >>> >> >> > via
>>>> >>>> >>> >> >> > an SCC pass, enabled only under -fthinlto options. The
>>>> pass
>>>> >>>> >>> >> >> > includes
>>>> >>>> >>> >> >> > utilizing the thin archive (global function
>>>> index/summary),
>>>> >>>> >>> >> >> > import
>>>> >>>> >>> >> >> > decision heuristics, invocation of
>>>> LTOModule/ModuleLinker
>>>> >>>> >>> >> >> > routines
>>>> >>>> >>> >> >> > that perform the import, and any necessary callgraph
>>>> updates
>>>> >>>> >>> >> >> > and
>>>> >>>> >>> >> >> > verification.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > g. Backend Driver:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > For a single node build, the gold plugin can simply
>>>> write a
>>>> >>>> >>> >> >> > makefile
>>>> >>>> >>> >> >> > and fork the parallel backend instances directly via
>>>> >>>> >>> >> >> > parallel
>>>> >>>> >>> >> >> > make.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > 3. Stage 3: ThinLTO Tuning and Enhancements
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> ----------------------------------------------------------------
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > This refers to the patches that are not required for
>>>> ThinLTO
>>>> >>>> >>> >> >> > to
>>>> >>>> >>> >> >> > work,
>>>> >>>> >>> >> >> > but rather to improve compile time, memory, run-time
>>>> >>>> >>> >> >> > performance
>>>> >>>> >>> >> >> > and
>>>> >>>> >>> >> >> > usability.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > a. Lazy Debug Metadata Linking:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > The prototype implementation included lazy importing of
>>>> >>>> >>> >> >> > module-level
>>>> >>>> >>> >> >> > metadata during the ThinLTO pass finalization (i.e.
>>>> after
>>>> >>>> >>> >> >> > all
>>>> >>>> >>> >> >> > function
>>>> >>>> >>> >> >> > importing is complete). This actually applies to all
>>>> >>>> >>> >> >> > module-level
>>>> >>>> >>> >> >> > metadata, not just debug, although it is the largest.
>>>> This
>>>> >>>> >>> >> >> > can be
>>>> >>>> >>> >> >> > added as a separate set of patches. Changes to
>>>> >>>> >>> >> >> > BitcodeReader,
>>>> >>>> >>> >> >> > ValueMapper, ModuleLinker
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > b. Import Tuning:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > Tuning the import strategy will be an iterative
>>>> process that
>>>> >>>> >>> >> >> > will
>>>> >>>> >>> >> >> > continue to be refined over time. It involves several
>>>> >>>> >>> >> >> > different
>>>> >>>> >>> >> >> > types
>>>> >>>> >>> >> >> > of changes: adding support for recording additional
>>>> metrics
>>>> >>>> >>> >> >> > in
>>>> >>>> >>> >> >> > the
>>>> >>>> >>> >> >> > function summary, such as profile data and optional
>>>> >>>> >>> >> >> > heavier-weight
>>>> >>>> >>> >> >> > IPA
>>>> >>>> >>> >> >> > analyses, and tuning the import heuristics based on the
>>>> >>>> >>> >> >> > summary
>>>> >>>> >>> >> >> > and
>>>> >>>> >>> >> >> > callsite context.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > c. Combined Function Map Pruning:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > The combined function map can be pruned of functions
>>>> that
>>>> >>>> >>> >> >> > are
>>>> >>>> >>> >> >> > unlikely
>>>> >>>> >>> >> >> > to benefit from being imported. For example, during the
>>>> >>>> >>> >> >> > phase-2
>>>> >>>> >>> >> >> > thin
>>>> >>>> >>> >> >> > archive plug step we can safely omit large and (with
>>>> profile
>>>> >>>> >>> >> >> > data)
>>>> >>>> >>> >> >> > cold functions, which are unlikely to benefit from
>>>> being
>>>> >>>> >>> >> >> > inlined.
>>>> >>>> >>> >> >> > Additionally, all but one copy of comdat functions can
>>>> be
>>>> >>>> >>> >> >> > suppressed.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > d. Distributed Build System Integration:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > For a distributed build system, the gold plugin should
>>>> write
>>>> >>>> >>> >> >> > the
>>>> >>>> >>> >> >> > parallel backend invocations into a makefile,
>>>> including the
>>>> >>>> >>> >> >> > mapping
>>>> >>>> >>> >> >> > from the IR file to the real object file path, and
>>>> exit.
>>>> >>>> >>> >> >> > Additional
>>>> >>>> >>> >> >> > work needs to be done in the distributed build system
>>>> itself
>>>> >>>> >>> >> >> > to
>>>> >>>> >>> >> >> > distribute and dispatch the parallel backend jobs to
>>>> the
>>>> >>>> >>> >> >> > build
>>>> >>>> >>> >> >> > cluster.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > e. Dependence Tracking and Incremental Compiles:
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > In order to support build systems that stage from local
>>>> >>>> >>> >> >> > disks or
>>>> >>>> >>> >> >> > network storage, the plugin will optionally support
>>>> >>>> >>> >> >> > computation
>>>> >>>> >>> >> >> > of
>>>> >>>> >>> >> >> > dependent sets of IR files that each module may import
>>>> from.
>>>> >>>> >>> >> >> > This
>>>> >>>> >>> >> >> > can
>>>> >>>> >>> >> >> > be computed from profile data, if it exists, or from
>>>> the
>>>> >>>> >>> >> >> > symbol
>>>> >>>> >>> >> >> > table
>>>> >>>> >>> >> >> > and heuristics if not. These dependence sets also
>>>> enable
>>>> >>>> >>> >> >> > support
>>>> >>>> >>> >> >> > for
>>>> >>>> >>> >> >> > incremental backend compiles.
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > --
>>>> >>>> >>> >> >> > Teresa Johnson | Software Engineer |
>>>> tejohnson at google.com |
>>>> >>>> >>> >> >> > 408-460-2413
>>>> >>>> >>> >> >> >
>>>> >>>> >>> >> >> > _______________________________________________
>>>> >>>> >>> >> >> > LLVM Developers mailing list
>>>> >>>> >>> >> >> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> >>>> >>> >> >> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>> >>>> >>> >> >>
>>>> >>>> >>> >> >> _______________________________________________
>>>> >>>> >>> >> >> LLVM Developers mailing list
>>>> >>>> >>> >> >> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> >>>> >>> >> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>> >>>> >>> >> >
>>>> >>>> >>> >> >
>>>> >>>> >>> >>
>>>> >>>> >>> >>
>>>> >>>> >>> >>
>>>> >>>> >>> >> --
>>>> >>>> >>> >> Teresa Johnson | Software Engineer | tejohnson at google.com |
>>>> >>>> >>> >> 408-460-2413
>>>> >>>> >>> >>
>>>> >>>> >>> >> _______________________________________________
>>>> >>>> >>> >> LLVM Developers mailing list
>>>> >>>> >>> >> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> >>>> >>> >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>> >>>> >>>
>>>> >>>> >>>
>>>> >>>> >>>
>>>> >>>> >>> --
>>>> >>>> >>> Teresa Johnson | Software Engineer | tejohnson at google.com |
>>>> >>>> >>> 408-460-2413
>>>> >>>> >>
>>>> >>>> >>
>>>> >>>> >
>>>> >>>> > _______________________________________________
>>>> >>>> > LLVM Developers mailing list
>>>> >>>> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> >>>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>> >>>> >
>>>> >>>
>>>> >>>
>>>> >>> _______________________________________________
>>>> >>> LLVM Developers mailing list
>>>> >>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> >>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>> >>>
>>>> >
>>>> > _______________________________________________
>>>> > LLVM Developers mailing list
>>>> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>> >
>>>>
>>>>
>>>>
>>>> --
>>>> Teresa Johnson | Software Engineer | tejohnson at google.com |
>>>> 408-460-2413
>>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150515/1842c0bc/attachment.html>