Add a lower level zlib::uncompress

[• rafael]

Summary

SmallVectors are convenient, but they don't cover every use case.

In particular, they are fairly large (3 pointers + one element) and there is no way to take ownership of the buffer to put it somewhere else.
This patch then adds a lower lever interface that works with any buffer.

[ruiu]

include/llvm/Support/Compression.h

46

uint8_t * is better than char *, no?

[• rafael]

include/llvm/Support/Compression.h

46

Probably not in here since the rest of the API uses SmallVectorImpl<char>. We could change the rest to use SmallVectorImpl<uint8_t>, but should be another patch.

[ruiu]

LGTM

[• rafael]

r281082

include/llvm/Support/Compression.h

enum Status {
   StatusInvalidData     // data was corrupted or incomplete
 };
 
 bool isAvailable();
 
 Status compress(StringRef InputBuffer, SmallVectorImpl<char> &CompressedBuffer,
                 CompressionLevel Level = DefaultCompression);
 
+Status uncompress(StringRef InputBuffer, char *UncompressedBuffer,
+                  size_t &UncompressedSize);
+
 Status uncompress(StringRef InputBuffer,
                   SmallVectorImpl<char> &UncompressedBuffer,
                   size_t UncompressedSize);
 
 uint32_t crc32(StringRef Buffer);
 
 }  // End of namespace zlib
 
 } // End of namespace llvm
 
 #endif
 

lib/Support/Compression.cpp

Status Res = encodeZlibReturnValue(::compress2(
       (const Bytef *)InputBuffer.data(), InputBuffer.size(), CLevel));
   // 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;
 }
 
+zlib::Status zlib::uncompress(StringRef InputBuffer, char *UncompressedBuffer,
+                              size_t &UncompressedSize) {
+  Status Res = encodeZlibReturnValue(
+      ::uncompress((Bytef *)UncompressedBuffer, (uLongf *)&UncompressedSize,
+                   (const Bytef *)InputBuffer.data(), InputBuffer.size()));
+  // Tell MemorySanitizer that zlib output buffer is fully initialized.
+  // This avoids a false report when running LLVM with uninstrumented ZLib.
+  __msan_unpoison(UncompressedBuffer, UncompressedSize);
+  return Res;
+}
+
 zlib::Status zlib::uncompress(StringRef InputBuffer,
                               SmallVectorImpl<char> &UncompressedBuffer,
                               size_t UncompressedSize) {
   UncompressedBuffer.resize(UncompressedSize);
-  Status Res = encodeZlibReturnValue(::uncompress(
-      (Bytef *)UncompressedBuffer.data(), (uLongf *)&UncompressedSize,
-      (const Bytef *)InputBuffer.data(), InputBuffer.size()));
-  // Tell MemorySanitizer that zlib output buffer is fully initialized.
-  // This avoids a false report when running LLVM with uninstrumented ZLib.
-  __msan_unpoison(UncompressedBuffer.data(), UncompressedSize);
+  Status Res =
+      uncompress(InputBuffer, UncompressedBuffer.data(), UncompressedSize);
   UncompressedBuffer.resize(UncompressedSize);
   return Res;
 }
 
 uint32_t zlib::crc32(StringRef Buffer) {
   return ::crc32(0, (const Bytef *)Buffer.data(), Buffer.size());
 }