[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

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/lib/Support/Compression.cpp b/llvm/lib/Support/Compression.cpp
index e8fb715..9a04716 100644
--- a/llvm/lib/Support/Compression.cpp
+++ b/llvm/lib/Support/Compression.cpp
@@ -27,6 +27,52 @@
 using namespace llvm;
 using namespace llvm::compression;
 
+const char *compression::getReasonIfUnsupported(compression::Format F) {
+  switch (F) {
+  case compression::Format::Zlib:
+    if (zlib::isAvailable())
+      return nullptr;
+    return "LLVM was not built with LLVM_ENABLE_ZLIB or did not find zlib at "
+           "build time";
+  case compression::Format::Zstd:
+    if (zstd::isAvailable())
+      return nullptr;
+    return "LLVM was not built with LLVM_ENABLE_ZSTD or did not find zstd at "
+           "build time";
+  }
+  llvm_unreachable("");
+}
+
+void compression::compress(Params P, ArrayRef<uint8_t> Input,
+                           SmallVectorImpl<uint8_t> &Output) {
+  switch (P.format) {
+  case compression::Format::Zlib:
+    zlib::compress(Input, Output, P.level);
+    break;
+  case compression::Format::Zstd:
+    zstd::compress(Input, Output, P.level);
+    break;
+  }
+}
+
+Error compression::decompress(compression::Format F, ArrayRef<uint8_t> Input,
+                              SmallVectorImpl<uint8_t> &Output,
+                              size_t UncompressedSize) {
+  switch (F) {
+  case compression::Format::Zlib:
+    return zlib::uncompress(Input, Output, UncompressedSize);
+  case compression::Format::Zstd:
+    return zstd::uncompress(Input, Output, UncompressedSize);
+  }
+  llvm_unreachable("");
+}
+
+Error compression::decompress(DebugCompressionType T, ArrayRef<uint8_t> Input,
+                              SmallVectorImpl<uint8_t> &Output,
+                              size_t UncompressedSize) {
+  return decompress(formatFor(T), Input, Output, UncompressedSize);
+}
+
 #if LLVM_ENABLE_ZLIB
 
 static StringRef convertZlibCodeToString(int Code) {