This intrinsic is used when whole program vtables is used in conjunction
with either CFI or virtual function elimination. The
`llvm.type.checked.load` is unconditionally used, but we need to use the
relative intrinsic for WPD and CFI to work correctly.
When using FatLTO, it is common to want to enable certain types of whole
program optimizations (WPD) or security transforms (CFI), so that they
can be made available when performing LTO. However, these transforms
should not be used when compiling the non-LTO object code. Since the
frontend must emit different IR, we cannot simply clone the module and
optimize the LTO section and non-LTO section differently to work around
this. Instead, we need to remove any problematic instruction sequences.
This patch adds a new pass whose responsibility is to clean up the IR
in the FatLTO pipeline after creating the bitcode section, which is
after running the pre-link pipeline but before running module
optimization. This allows us to safely drop any conflicting instructions
or IR constructs that are inappropriate for non-LTO compilation.
We want to support CFI instrumentation for the bitcode section, without
miscompiling the object code portion of a FatLTO object. We can reuse
the existing mechanisms in the LowerTypeTestsPass to do that, by just
adding the pass to the FatLTO pipeline after the EmbedBitcodePass with
the correct options set.
Fixes#112053
