[llvm] r191042 - Fix LTO handling of module-level assembly (PR14152).

Tom Roeder tmroeder at google.com
Mon Sep 23 12:20:04 PDT 2013

I think it could be refactored along these lines. I was hoping for
clients of the library not to have to know about the dependency but
simply to get it implicitly by depending on lib/LTO. Is there a way to
do this using llvm-build?

After looking through the code a bit, I see that the only callers of
the InitializeAll* routines are in tools/. So, if this is the existing
design direction, then I'll see about pulling those parts up into
clients of lib/LTO.


On Mon, Sep 23, 2013 at 11:50 AM, Daniel Dunbar <daniel at zuster.org> wrote:
> Hi Tom,
> Can you explain why lib/LTO needs to depend on all-targets? I'm not sure we
> actually want this behavior, what we generally want is that clients can pick
> the library and then pick the list of targets that get included. In this
> case, I think the right thing that should happen is that both tools/lto and
> llvm-lto depend on all targets and handle the target initialization, whereas
> lib/LTO itself just relies on the targets already having been initialized.
> Is it possible to factor lib/LTO in that fashion?
>  - Daniel
> On Fri, Sep 20, 2013 at 11:59 PM, Tom Roeder <tmroeder at google.com> wrote:
>> I've written a patch now (in consultation with Peter) that does
>> exactly this: tools/llvm-lto is split into a lib/LTO component and a
>> tools/llvm-lto component, and tools/llvm-lto is written to depend only
>> on lib/LTO (and not tools/lto, hence not libLTO.so). This should solve
>> the problems with the freebsd build and additionally be a better
>> factorization of the code.
>> However, this design led to an interesting problem: lib/LTO needs to
>> depend on all-targets, and having a library that depends on
>> all-targets wasn't supported by the existing llvm-build scripts (the
>> required_libraries of all-targets came up with empty
>> required_libraries of their own). So, I've modified
>> llvm-build/llvmbuild/main.py to fill out these implicit dependencies,
>> using the information from the add_to_library_groups entries in the
>> LLVMBuild.txt files.
>> I've run clean builds with cmake/ninja, cmake/make, and Makefile and
>> run check successfully on each of them (on Linux). And I've built
>> LLVMgold.so against the Makefile version and tested it on a simple
>> test file (the test case from this patch).
>> However, my patch as it stands combines svn mv operations with edits
>> on the moved files, so it's far more verbose than necessary and loses
>> some of the history information (by not exactly capturing the move
>> information). Would you like me to formulate this as two patches: a
>> move followed by edits?
>> Please let me know what you think.
>> Thanks,
>> Tom
>> On Fri, Sep 20, 2013 at 12:50 PM, Peter Collingbourne <peter at pcc.me.uk>
>> wrote:
>> > On Fri, Sep 20, 2013 at 12:25:17PM -0700, Tom Roeder wrote:
>> >> Actually, it looks like libLTO.so simply isn't getting built or found
>> >> here
>> >> and that's why the test is failing.
>> >
>> > Hm?  The compile log:
>> >
>> > http://lab.llvm.org:8011/builders/clang-X86_64-freebsd/builds/10381/steps/compile/logs/stdio
>> > seems to indicate that libLTO is being built.
>> >
>> > I suspect that the problem is that the rpath isn't being embedded
>> > in the llvm-lto binary on FreeBSD in the correct way, though I can't
>> > tell for sure, since I don't have access to a FreeBSD machine.
>> >
>> > I'm beginning to think that the right way to solve this problem is
>> > to move LTOCodeGenerator.cpp and LTOModule.cpp in tools/lto into
>> > a new component 'lto' in lib/LTO and have tools/lto (which would
>> > then contain only the C interface) and tools/llvm-lto (and maybe
>> > tools/gold in the future) depend on the lto component.  That way,
>> > the LTO support library is no different to any other component of
>> > LLVM and is less likely to cause problems across platforms.
>> >
>> > Thanks,
>> > --
>> > Peter
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