[PATCH] D59269: ELF: Use bump pointer allocator for uncompressed section buffers. NFCI.

[Peter Collingbourne via Phabricator via llvm-commits]

pcc created this revision.
pcc added reviewers: ruiu, grimar.
Herald added subscribers: jdoerfert, MaskRay, arichardson, emaste.
Herald added a reviewer: espindola.
Herald added a project: LLVM.

This shaves another word off SectionBase and makes it possible to clone a
section using the implicit copy constructor.

This basically reverts r311056, which removed the mutex in order to
make the code easier to understand. On balance I think it's probably more
straightforward to have a mutex here than to have an unusual copy constructor
in SectionBase.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D59269

Files:
  lld/ELF/InputSection.cpp
  lld/ELF/InputSection.h


Index: lld/ELF/InputSection.h
===================================================================
--- lld/ELF/InputSection.h
+++ lld/ELF/InputSection.h
@@ -133,7 +133,7 @@
   }
 
   ArrayRef<uint8_t> data() const {
-    if (UncompressedSize >= 0 && !UncompressedBuf)
+    if (UncompressedSize >= 0)
       uncompress();
     return RawData;
   }
@@ -210,10 +210,11 @@
 
   mutable ArrayRef<uint8_t> RawData;
 
-  // A pointer that owns uncompressed data if a section is compressed by zlib.
-  // Since the feature is not used often, this is usually a nullptr.
-  mutable std::unique_ptr<char[]> UncompressedBuf;
-  int64_t UncompressedSize = -1;
+  // This field stores the uncompressed size of the compressed data in RawData,
+  // or -1 if RawData is not compressed (either because the section wasn't
+  // compressed in the first place, or because we ended up uncompressing it).
+  // Since the feature is not used often, this is usually -1.
+  mutable int64_t UncompressedSize = -1;
 };
 
 // SectionPiece represents a piece of splittable section contents.
Index: lld/ELF/InputSection.cpp
===================================================================
--- lld/ELF/InputSection.cpp
+++ lld/ELF/InputSection.cpp
@@ -144,13 +144,18 @@
 
 void InputSectionBase::uncompress() const {
   size_t Size = UncompressedSize;
-  UncompressedBuf.reset(new char[Size]);
+  char *UncompressedBuf;
+  {
+    static std::mutex Mu;
+    std::lock_guard<std::mutex> Lock(Mu);
+    UncompressedBuf = BAlloc.Allocate<char>(Size);
+  }
 
-  if (Error E =
-          zlib::uncompress(toStringRef(RawData), UncompressedBuf.get(), Size))
+  if (Error E = zlib::uncompress(toStringRef(RawData), UncompressedBuf, Size))
     fatal(toString(this) +
           ": uncompress failed: " + llvm::toString(std::move(E)));
-  RawData = makeArrayRef((uint8_t *)UncompressedBuf.get(), Size);
+  RawData = makeArrayRef((uint8_t *)UncompressedBuf, Size);
+  UncompressedSize = -1;
 }
 
 uint64_t InputSectionBase::getOffsetInFile() const {
@@ -1062,7 +1067,7 @@
 
   // If this is a compressed section, uncompress section contents directly
   // to the buffer.
-  if (UncompressedSize >= 0 && !UncompressedBuf) {
+  if (UncompressedSize >= 0) {
     size_t Size = UncompressedSize;
     if (Error E = zlib::uncompress(toStringRef(RawData),
                                    (char *)(Buf + OutSecOff), Size))


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