Apologies for the large change, I looked for ways to break this up and
all of the ones I saw added real complexity. This change focuses on the
option's prefixed names and the array of prefixes. These are present in
every option and the dominant source of dynamic relocations for PIE or
PIC users of LLVM and Clang tooling. In some cases, 100s or 1000s of
them for the Clang driver which has a huge number of options.
This PR addresses this by building a string table and a prefixes table
that can be referenced with indices rather than pointers that require
dynamic relocations. This removes almost 7k dynmaic relocations from the
`clang` binary, roughly 8% of the remaining dynmaic relocations outside
of vtables. For busy-boxing use cases where many different option tables
are linked into the same binary, the savings add up a bit more.
The string table is a straightforward mechanism, but the prefixes
required some subtlety. They are encoded in a Pascal-string fashion with
a size followed by a sequence of offsets. This works relatively well for
the small realistic prefixes arrays in use.
Lots of code has to change in order to land this though: both all the
option library code has to be updated to use the string table and
prefixes table, and all the users of the options library have to be
updated to correctly instantiate the objects.
Some follow-up patches in the works to provide an abstraction for this
style of code, and to start using the same technique for some of the
other strings here now that the infrastructure is in place.
While porting the tool from using cl:opt to OptTable, I had mistakenly
deleted the help text header that was originally part of the tool.
Bringing it back in this patch.
This patch removes a comment in llvm-debuginfod-find containing all the
cl::opt entries, which are redundant after the conversion to using
optTable. These seem to have been introduced in #108082 along with a
conversion to optTable.
In preparation for removing the `#include "llvm/ADT/StringExtras.h"`
from the header to source file of `llvm/Support/Error.h`, first add in
all the missing includes that were previously included transitively
through this header.
This creates a library for fetching debug info by build ID, whether
locally or remotely via debuginfod. The functionality was refactored
out of existing code in the Symboliize library. Existing utilities
were refactored to use this library.
Reviewed By: phosek
Differential Revision: https://reviews.llvm.org/D132504
This allows llvm-debuginfod-find to locate binaries in local build ID
directories configured via --debug-file-directory, the same flag used
for this purpose by llvm-symbolizer. This provides a consistent lookup
semantics between the two tools when configured the same way, in
particular when debug binaries may be located either locally or
remotely.
Reviewed By: phosek
Differential Revision: https://reviews.llvm.org/D125864
