[CodeGen] Generate DWARF v5 Accelerator Tables

Summary:
This patch adds a DwarfAccelTableEmitter class, which generates an
accelerator table, as specified in DWARF v5 standard. At the moment it
only generates a DIE offset column and (if we are indexing more than one
compile unit) a CU column.

Indexing type units is not currently supported, as we don't even have
the ability to generate DWARF v5-compatible compile units.

The implementation is not data-source agnostic like the one generating
apple tables. This was not necessary as we currently only have one user
of this code, and without a second user it was not obvious to me how to
best abstract this. (The difference between these tables and the apple
ones is that they need a lot more metadata about the debug info they are
indexing).

The generation is triggered by the --accel-tables argument, which
supersedes the --dwarf-accel-tables arg -- the latter was a simple
on-off switch, but not we can choose between two kinds of accelerator
tables we can generate.

This is tested by parsing the generated tables with llvm-dwarfdump and
the DWARFVerifier, and I've also checked that GNU readelf is able to
make sense of the tables.

Differential Revision: https://reviews.llvm.org/D43286

llvm-svn: 329179

0 files changed, 0 insertions, 0 deletions