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
