[Debuginfo][SROA] (7/7) Support for DW_OP_implicit_pointer for named and unnamed variables (second strategy).

[alok]

Summary

This patch stems from D84112.
This patch includes changes for SROA optimization.

[jmorse]

I see what seem to be changes to codegen here (see inline comments), is that intentional? And if so, why is that needed for DW_OP_LLVM_explicit_pointer to work?

llvm/lib/IR/Metadata.cpp

395

Why is this now permitted behaviour?

llvm/lib/Transforms/Scalar/EarlyCSE.cpp

1648–1654

Is this necessary for the implicit pointer work?

llvm/lib/Transforms/Scalar/SROA.cpp

4419–4503

Again, this block of code will need comments about its purpose adding.

4449–4453

This part looks like it's changing the code generated, replacing a GEP with an alloca. If that's the case, IMO this should be split out into a different patch (one for codegen, one for debuginfo), as any codegen change will need an independent argument as to why it's a good idea.

Plus, this would only be a codegen change for people building with dwarf-5, which would mean you get different code with and without the -g option to clang.

llvm/lib/Transforms/Utils/PromoteMemoryToRegister.cpp

424 ↗

(On Diff #279045)

This should be folded into the previous patch (7?)

[alok]

Updated to re-base.