Always read bitcode according to the -opaque-pointers mode. Do not
perform auto-detection to implicitly switch to typed pointers.
This is a step towards removing typed pointer support, and also
eliminates the class of problems where linking may fail if a typed
pointer module is loaded before an opaque pointer module. (The
latest place where this was encountered is D139924, but this has
previously been fixed in other places doing bitcode linking as well.)
Differential Revision: https://reviews.llvm.org/D139940
With Control-Flow Integrity (CFI), the LowerTypeTests pass replaces
function references with CFI jump table references, which is a problem
for low-level code that needs the address of the actual function body.
For example, in the Linux kernel, the code that sets up interrupt
handlers needs to take the address of the interrupt handler function
instead of the CFI jump table, as the jump table may not even be mapped
into memory when an interrupt is triggered.
This change adds the no_cfi constant type, which wraps function
references in a value that LowerTypeTestsModule::replaceCfiUses does not
replace.
Link: https://github.com/ClangBuiltLinux/linux/issues/1353
Reviewed By: nickdesaulniers, pcc
Differential Revision: https://reviews.llvm.org/D108478
