[llvm] r338913 - [Support] Don't initialize compressed buffer allocated by zlib::compress

[Fangrui Song via llvm-commits]

Author: maskray
Date: Fri Aug  3 12:37:49 2018
New Revision: 338913

URL: http://llvm.org/viewvc/llvm-project?rev=338913&view=rev
Log:
[Support] Don't initialize compressed buffer allocated by zlib::compress

resize() (zeroing) makes every allocated page resident. The actual size of the compressed buffer is usually much
smaller. Making every page resident is wasteful.

When linking a test binary with ~1.9GiB uncompressed debug info with LLD, this optimization decreases max RSS by ~1.5GiB.

Differential Revision: https://reviews.llvm.org/50223

Modified:
    llvm/trunk/lib/Support/Compression.cpp

Modified: llvm/trunk/lib/Support/Compression.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Compression.cpp?rev=338913&r1=338912&r2=338913&view=diff
==============================================================================
--- llvm/trunk/lib/Support/Compression.cpp (original)
+++ llvm/trunk/lib/Support/Compression.cpp Fri Aug  3 12:37:49 2018
@@ -61,7 +61,7 @@ Error zlib::compress(StringRef InputBuff
                      SmallVectorImpl<char> &CompressedBuffer,
                      CompressionLevel Level) {
   unsigned long CompressedSize = ::compressBound(InputBuffer.size());
-  CompressedBuffer.resize(CompressedSize);
+  CompressedBuffer.reserve(CompressedSize);
   int CLevel = encodeZlibCompressionLevel(Level);
   int Res = ::compress2((Bytef *)CompressedBuffer.data(), &CompressedSize,
                         (const Bytef *)InputBuffer.data(), InputBuffer.size(),
@@ -69,7 +69,7 @@ Error zlib::compress(StringRef InputBuff
   // 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);
+  CompressedBuffer.set_size(CompressedSize);
   return Res ? createError(convertZlibCodeToString(Res)) : Error::success();
 }