[PATCH] D133392: [MTE] Add AArch64GlobalsTagging Pass

[Mitch Phillips via Phabricator via cfe-commits]

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Adds the IR pass to tag global variables. You can see the official ABI
proposal at https://github.com/ARM-software/abi-aa/pull/166.

This pass very simply goes over the taggable global variables, re-sizes
and re-aligns them so that they're matched up to the tag granule size
(16 bytes), and marks them as tagged. This allows the backend to create
relocations and put them into a special section.

Global merge must be suppressed for tagged globals, as each global
variable must have a unique tag. This can possibly be relaxed in future;
globals that are identical in size, alignment, and content can
possibly be merged. The major problem comes from tail- or head-merging.

In addition, make sure that tagged globals in object files have
referenced symtab entries for relocations. This is necessary for the
linker to know where a tag should come from, as there's some special
dynamic relocation logic that applies
(https://github.com/ARM-software/abi-aa/blob/64458f8608b69536880501caced7c95a10a49d24/memtagabielf64/memtagabielf64.rst#extended-semantics-of-r-aarch64-relative)


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D133392

Files:
  clang/test/CodeGen/memtag-globals-asm.cpp
  llvm/lib/CodeGen/GlobalMerge.cpp
  llvm/lib/MC/ELFObjectWriter.cpp
  llvm/lib/Target/AArch64/AArch64.h
  llvm/lib/Target/AArch64/AArch64GlobalsTagging.cpp
  llvm/lib/Target/AArch64/AArch64Subtarget.cpp
  llvm/lib/Target/AArch64/AArch64TargetMachine.cpp
  llvm/lib/Target/AArch64/CMakeLists.txt
  llvm/test/CodeGen/AArch64/O0-pipeline.ll
  llvm/test/CodeGen/AArch64/O3-pipeline.ll

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