This patch prevents thread-local constants to be merged within
PPCMergeStringPool.cpp.
The PPCMergeStringPool pass primarily merges non-thread-local constants
together, and thread-local constants should not be mixed together with
other (non-thread-local) constants. In the event that thread-local and
other non-thread-local constants are pooled together, the
llvm.threadlocal.address intrinsic can fail as it expects its argument
to be a thread-local global value, but the merged string structure
created by the PPCMergeStringPool pass is not thread-local as a whole.
In #88846 I changed this code to use RAUW to perform the replacement
instead of manual updates -- but kept the outer loop, which means we try
to perform RAUW once per user. However, some of the users might be freed
by the RAUW operation, resulting in use-after-free.
The case where this happens is constant users where the replacement
might result in the destruction of the original constant.
Fixes https://github.com/llvm/llvm-project/issues/92991.
String pool merging currently, for a reason that's not entirely clear to
me, tries to create GEP instructions instead of GEP constant expressions
when replacing constant references. It only uses constant expressions in
cases where this is required. However, it does not catch all cases where
such a requirement exists. For example, the landingpad catch clause has
to be a constant.
Fix this by always using the constant expression variant, which also
makes the implementation simpler.
Additionally, there are some edge cases where even replacement with a
constant GEP is not legal. The one I am aware of is the
llvm.eh.typeid.for intrinsic, so add a special case to forbid
replacements for it.
Fixes https://github.com/llvm/llvm-project/issues/88844.
Currently, the `PPCMergeStringPool` merges the global variable after the
`AsmPrinter` initializer adds the global variables to its symbol list.
This is to move the merging work of `PPCMergeStringPool` to its
initializer, just like what GlobalMerge does, to avoid adding merged
global variables to the `AsmPrinter` symbol lis.
Currently if the merged string is used by metadata, its metadata uses
are not replaced if the string is merged. This is to add code support
for the metadata use replacement.
The string pooling pass was incorrectly pooling global varables that
were part of llvm.used or llvm.compiler.used. This patch fixes the pass
to prevent that by checking each candidate to make sure that it is not
in either of those lists.
On PowerPC the number of TOC entries must be kept low for large
applications. In order to reduce the number of constant global arrays
we can pool them into one structure and then access them as the base
address of that structure plus some offset. The constant global arrays
may be arrays of `i8` which are constant strings but they may also be
arrays of `i32, i64, etc...`.
Reviewed By: lei, amyk
Differential Revision: https://reviews.llvm.org/D155730
