From bc4d1a36047bae030871accdaf51c943304ef342 Mon Sep 17 00:00:00 2001 From: Alp Toker Date: Fri, 11 Jul 2014 14:02:04 +0000 Subject: [PATCH] raw_svector_ostream: grow and reserve atomically Including the scratch buffer size in the initial reservation eliminates the subsequent malloc+move operation and offers a healthier constant growth with less memory wastage. When doing this, take care to avoid invalidating the source buffer. llvm-svn: 212816 --- llvm/lib/Support/raw_ostream.cpp | 32 +++++++++++++++++--------------- 1 file changed, 17 insertions(+), 15 deletions(-) diff --git a/llvm/lib/Support/raw_ostream.cpp b/llvm/lib/Support/raw_ostream.cpp index f7c213a..b8a1537 100644 --- a/llvm/lib/Support/raw_ostream.cpp +++ b/llvm/lib/Support/raw_ostream.cpp @@ -729,24 +729,26 @@ void raw_svector_ostream::resync() { } void raw_svector_ostream::write_impl(const char *Ptr, size_t Size) { - // If we're writing bytes from the end of the buffer into the smallvector, we - // don't need to copy the bytes, just commit the bytes because they are - // already in the right place. - if (Ptr == OS.end()) { - assert(OS.size() + Size <= OS.capacity() && "Invalid write_impl() call!"); - OS.set_size(OS.size() + Size); + size_t NewSize = OS.size() + Size; + size_t NewReservation = NewSize + 64; + + bool NoOverlap = Ptr + Size < OS.begin() || Ptr > OS.begin() + OS.capacity(); + + if (NoOverlap) { + assert(!GetNumBytesInBuffer()); + OS.reserve(NewReservation); + memcpy(OS.end(), Ptr, Size); + OS.set_size(NewSize); + } else if (Ptr == OS.end()) { + // Grow the buffer to include the scratch area without copying. + assert(NewSize <= OS.capacity() && "Invalid write_impl() call!"); + OS.set_size(NewSize); + OS.reserve(NewReservation); } else { - assert(GetNumBytesInBuffer() == 0 && - "Should be writing from buffer if some bytes in it"); - // Otherwise, do copy the bytes. - OS.append(Ptr, Ptr+Size); + OS.append(Ptr, Ptr + Size); + OS.reserve(NewReservation); } - // Grow the vector if necessary. - if (OS.capacity() - OS.size() < 64) - OS.reserve(OS.capacity() * 2); - - // Update the buffer position. SetBuffer(OS.end(), OS.capacity() - OS.size()); } -- 2.7.4