Use the same constants as zlib to represent compression level.

[ruiu]

Summary

This change allows users pass compression level that was not listed
in the enum. Also, I think using different values than zlib's
compression levels was just confusing.

[pcc]

LGTM

[dblaikie]

Looks like this change removes/reduces some type safety - by moving to an
int parameter.

Could the enum be kept, but with all the values supported? (an enum's
representable values includes at least (actually more than - round up to
the nearest number of bits required) all the values smaller than the
largest enumerator - so an enum with the BestSize value will be usable for
all the others (eg: even with an enum class which doesn't allow implicit
conversions, a user could write (CompressionLevel)3 to get that specific
level).

llvm/include/llvm/Support/Compression.h

 
 namespace llvm {
 template <typename T> class SmallVectorImpl;
 class Error;
 class StringRef;
 
 namespace zlib {
 
-enum CompressionLevel {
-  NoCompression,
-  DefaultCompression,
-  BestSpeedCompression,
-  BestSizeCompression
-};
+static constexpr int NoCompression = 0;
+static constexpr int BestSpeedCompression = 1;
+static constexpr int DefaultCompression = 6;
+static constexpr int BestSizeCompression = 9;
 
 bool isAvailable();
 
 Error compress(StringRef InputBuffer, SmallVectorImpl<char> &CompressedBuffer,
-               CompressionLevel Level = DefaultCompression);
+               int Level = DefaultCompression);
 
 Error uncompress(StringRef InputBuffer, char *UncompressedBuffer,
                  size_t &UncompressedSize);
 
 Error uncompress(StringRef InputBuffer,
                  SmallVectorImpl<char> &UncompressedBuffer,
                  size_t UncompressedSize);
 
 uint32_t crc32(StringRef Buffer);
 
 }  // End of namespace zlib
 
 } // End of namespace llvm
 
 #endif
-

llvm/lib/Support/Compression.cpp

 
 using namespace llvm;
 
 #if LLVM_ENABLE_ZLIB == 1 && HAVE_LIBZ
 static Error createError(StringRef Err) {
   return make_error<StringError>(Err, inconvertibleErrorCode());
 }
 
-static int encodeZlibCompressionLevel(zlib::CompressionLevel Level) {
-  switch (Level) {
-    case zlib::NoCompression: return 0;
-    case zlib::BestSpeedCompression: return 1;
-    case zlib::DefaultCompression: return Z_DEFAULT_COMPRESSION;
-    case zlib::BestSizeCompression: return 9;
-  }
-  llvm_unreachable("Invalid zlib::CompressionLevel!");
-}
-
 static StringRef convertZlibCodeToString(int Code) {
   switch (Code) {
   case Z_MEM_ERROR:
     return "zlib error: Z_MEM_ERROR";
   case Z_BUF_ERROR:
     return "zlib error: Z_BUF_ERROR";
   case Z_STREAM_ERROR:
     return "zlib error: Z_STREAM_ERROR";
   case Z_DATA_ERROR:
     return "zlib error: Z_DATA_ERROR";
   case Z_OK:
   default:
     llvm_unreachable("unknown or unexpected zlib status code");
   }
 }
 
 bool zlib::isAvailable() { return true; }
 
 Error zlib::compress(StringRef InputBuffer,
-                     SmallVectorImpl<char> &CompressedBuffer,
-                     CompressionLevel Level) {
+                     SmallVectorImpl<char> &CompressedBuffer, int Level) {
   unsigned long CompressedSize = ::compressBound(InputBuffer.size());
   CompressedBuffer.resize(CompressedSize);
-  int CLevel = encodeZlibCompressionLevel(Level);
-  int Res = ::compress2((Bytef *)CompressedBuffer.data(), &CompressedSize,
-                        (const Bytef *)InputBuffer.data(), InputBuffer.size(),
-                        CLevel);
+  int Res =
+      ::compress2((Bytef *)CompressedBuffer.data(), &CompressedSize,
+                  (const Bytef *)InputBuffer.data(), InputBuffer.size(), Level);
   // Tell MemorySanitizer that zlib output buffer is fully initialized.
   // This avoids a false report when running LLVM with uninstrumented ZLib.
   __msan_unpoison(CompressedBuffer.data(), CompressedSize);
   CompressedBuffer.resize(CompressedSize);
   return Res ? createError(convertZlibCodeToString(Res)) : Error::success();
 }
 
 Error zlib::uncompress(StringRef InputBuffer, char *UncompressedBuffer,
Error zlib::uncompress(StringRef InputBuffer,
                        SmallVectorImpl<char> &UncompressedBuffer,
                        size_t UncompressedSize) {
   llvm_unreachable("zlib::uncompress is unavailable");
 }
 uint32_t zlib::crc32(StringRef Buffer) {
   llvm_unreachable("zlib::crc32 is unavailable");
 }
 #endif
-

llvm/unittests/Support/CompressionTest.cpp

 #include "gtest/gtest.h"
 
 using namespace llvm;
 
 namespace {
 
 #if LLVM_ENABLE_ZLIB == 1 && HAVE_LIBZ
 
-void TestZlibCompression(StringRef Input, zlib::CompressionLevel Level) {
+void TestZlibCompression(StringRef Input, int Level) {
   SmallString<32> Compressed;
   SmallString<32> Uncompressed;
 
   Error E = zlib::compress(Input, Compressed, Level);
   EXPECT_FALSE(E);
   consumeError(std::move(E));
 
   // Check that uncompressed buffer is the same as original.