Commits on Dec 4, 2013

1. Store metadata separately in rlib files …

   Right now whenever an rlib file is linked against, all of the metadata from the
   rlib is pulled in to the final staticlib or binary. The reason for this is that
   the metadata is currently stored in a section of the object file. Note that this
   is intentional for dynamic libraries in order to distribute metadata bundled
   with static libraries.
   
   This commit alters the situation for rlib libraries to instead store the
   metadata in a separate file in the archive. In doing so, when the archive is
   passed to the linker, none of the metadata will get pulled into the result
   executable. Furthermore, the metadata file is skipped when assembling rlibs into
   an archive.
   
   The snag in this implementation comes with multiple output formats. When
   generating a dylib, the metadata needs to be in the object file, but when
   generating an rlib this needs to be separate. In order to accomplish this, the
   metadata variable is inserted into an entirely separate LLVM Module which is
   then codegen'd into a different location (foo.metadata.o). This is then linked
   into dynamic libraries and silently ignored for rlib files.
   
   While changing how metadata is inserted into archives, I have also stopped
   compressing metadata when inserted into rlib files. We have wanted to stop
   compressing metadata, but the sections it creates in object file sections are
   apparently too large. Thankfully if it's just an arbitrary file it doesn't
   matter how large it is.
   
   I have seen massive reductions in executable sizes, as well as staticlib output
   sizes (to confirm that this is all working).

   

   alexcrichton committed Dec 4, 2013
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