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[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

llvm-svn: 338913
This commit is contained in:
Fangrui Song 2018-08-03 19:37:49 +00:00
parent eaa18e60eb
commit 23310a89be
1 changed files with 2 additions and 2 deletions
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4
llvm/lib/Support/Compression.cpp
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@ -61,7 +61,7 @@ Error zlib::compress(StringRef InputBuffer,
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 InputBuffer,
// 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();
}