From 64729e56dcc98a52cfce71e874f057bb6a064b19 Mon Sep 17 00:00:00 2001 From: Chandler Carruth Date: Tue, 15 Apr 2014 21:34:12 +0000 Subject: [PATCH] [Allocator] Make the ContentCache object actually carry the 8-byte alignment constraint rather than using the allocator function's over alignment "feature". This was the only use of the "feature" which I plan to remove next. =] Attaching the alignment to the type seems cleaner and more principled anyways. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206324 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/clang/Basic/SourceManager.h | 15 +++++++++++++++ lib/Basic/SourceManager.cpp | 16 ++++------------ 2 files changed, 19 insertions(+), 12 deletions(-) diff --git a/include/clang/Basic/SourceManager.h b/include/clang/Basic/SourceManager.h index c2130acbc9..886ba03777 100644 --- a/include/clang/Basic/SourceManager.h +++ b/include/clang/Basic/SourceManager.h @@ -44,6 +44,7 @@ #include "llvm/ADT/IntrusiveRefCntPtr.h" #include "llvm/ADT/PointerIntPair.h" #include "llvm/ADT/PointerUnion.h" +#include "llvm/Support/AlignOf.h" #include "llvm/Support/Allocator.h" #include "llvm/Support/DataTypes.h" #include "llvm/Support/MemoryBuffer.h" @@ -89,6 +90,15 @@ namespace SrcMgr { DoNotFreeFlag = 0x02 }; + // Note that the first member of this class is an aligned character buffer + // to ensure that this class has an alignment of 8 bytes. This wastes + // 8 bytes for every ContentCache object, but each of these corresponds to + // a file loaded into memory, so the 8 bytes doesn't seem terribly + // important. It is quite awkward to fit this aligner into any other part + // of the class due to the lack of portable ways to combine it with other + // members. + llvm::AlignedCharArray<8, 1> NonceAligner LLVM_ATTRIBUTE_UNUSED; + /// \brief The actual buffer containing the characters from the input /// file. /// @@ -224,6 +234,11 @@ namespace SrcMgr { ContentCache &operator=(const ContentCache& RHS) LLVM_DELETED_FUNCTION; }; + // Assert that the \c ContentCache objects will always be 8-byte aligned so + // that we can pack 3 bits of integer into pointers to such objects. + static_assert(llvm::AlignOf::Alignment >= 8, + "ContentCache must be 8-byte aligned."); + /// \brief Information about a FileID, basically just the logical file /// that it represents and include stack information. /// diff --git a/lib/Basic/SourceManager.cpp b/lib/Basic/SourceManager.cpp index b78e9f596e..c78c285e31 100644 --- a/lib/Basic/SourceManager.cpp +++ b/lib/Basic/SourceManager.cpp @@ -436,12 +436,8 @@ SourceManager::getOrCreateContentCache(const FileEntry *FileEnt, ContentCache *&Entry = FileInfos[FileEnt]; if (Entry) return Entry; - // Nope, create a new Cache entry. Make sure it is at least 8-byte aligned - // so that FileInfo can use the low 3 bits of the pointer for its own - // nefarious purposes. - unsigned EntryAlign = llvm::AlignOf::Alignment; - EntryAlign = std::max(8U, EntryAlign); - Entry = ContentCacheAlloc.Allocate(1, EntryAlign); + // Nope, create a new Cache entry. + Entry = ContentCacheAlloc.Allocate(); if (OverriddenFilesInfo) { // If the file contents are overridden with contents from another file, @@ -468,12 +464,8 @@ SourceManager::getOrCreateContentCache(const FileEntry *FileEnt, /// memory buffer. This does no caching. const ContentCache* SourceManager::createMemBufferContentCache(const MemoryBuffer *Buffer) { - // Add a new ContentCache to the MemBufferInfos list and return it. Make sure - // it is at least 8-byte aligned so that FileInfo can use the low 3 bits of - // the pointer for its own nefarious purposes. - unsigned EntryAlign = llvm::AlignOf::Alignment; - EntryAlign = std::max(8U, EntryAlign); - ContentCache *Entry = ContentCacheAlloc.Allocate(1, EntryAlign); + // Add a new ContentCache to the MemBufferInfos list and return it. + ContentCache *Entry = ContentCacheAlloc.Allocate(); new (Entry) ContentCache(); MemBufferInfos.push_back(Entry); Entry->setBuffer(Buffer); -- 2.40.0