[Support] Add llvm::compression::{getReasonIfUnsupported,compress,decompress}

as high-level API on top of `llvm::compression::{zlib,zstd}::*`:

* getReasonIfUnsupported: return nullptr if the specified format is
  supported, or (if unsupported) a string like `LLVM was not built with LLVM_ENABLE_ZLIB ...`
* compress: dispatch to zlib::uncompress or zstd::uncompress
* decompress: dispatch to zlib::uncompress or zstd::uncompress

Move `llvm::DebugCompressionType` from MC to Support to avoid Support->MC cyclic
dependency. There are 40+ uses in llvm-project.

Add another enum class `llvm::compression::Format` to represent supported
compression formats, which may be a superset of ELF compression formats.

See D130458 (llvm-objcopy --{,de}compress-debug-sections for zstd) for a use
case.

Link: https://discourse.llvm.org/t/rfc-zstandard-as-a-second-compression-method-to-llvm/63399
("[RFC] Zstandard as a second compression method to LLVM")

---

Note: this patch alone will cause -Wswitch to llvm/lib/ObjCopy/ELF/ELFObject.cpp

Reviewed By: ckissane, dblaikie

Differential Revision: https://reviews.llvm.org/D130506

0 files changed, 0 insertions, 0 deletions