r206324 - [Allocator] Make the ContentCache object actually carry the 8-byte
Chandler Carruth
chandlerc at gmail.com
Wed Apr 16 04:11:50 PDT 2014
Blindly tried to fix this in r206373. A test case seems to indicate this
works. Let me know if you still see issues.
On Wed, Apr 16, 2014 at 3:28 AM, Chandler Carruth <chandlerc at gmail.com>wrote:
> On Wed, Apr 16, 2014 at 2:31 AM, Evgeniy Stepanov <
> eugeni.stepanov at gmail.com> wrote:
>
>> I see a flood of warnings in GCC 4.8 build about unused attribute
>> being unused. Looks like GCC does not need or understand this
>> attribute on member declarations. Do we need a new macro like
>> LLVM_ATTRIBUTE_UNUSED_MEMBER ?
>>
>
> Someone else mentioned this, but I can't reproduce it. I suspect it just
> needs the attribute in a different place, but I don't know how to debug it
> because I don't see it... Let me try more extreme measures.
>
>
>>
>> [44/588] Building CXX object
>> tools/clang/lib/Lex/CMakeFiles/clangLex.dir/PreprocessorLexer.cpp.o
>> In file included from ../tools/clang/lib/Lex/PreprocessorLexer.cpp:15:0:
>> ../tools/clang/include/clang/Basic/SourceManager.h:100:56: warning:
>> ‘__unused__’ attribute ignored [-Wattributes]
>> LLVM_ATTRIBUTE_UNUSED llvm::AlignedCharArray<8, 1> NonceAligner;
>> ^
>>
>> On Wed, Apr 16, 2014 at 1:34 AM, Chandler Carruth <chandlerc at gmail.com>
>> wrote:
>> > Author: chandlerc
>> > Date: Tue Apr 15 16:34:12 2014
>> > New Revision: 206324
>> >
>> > URL: http://llvm.org/viewvc/llvm-project?rev=206324&view=rev
>> > Log:
>> > [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.
>> >
>> > Modified:
>> > cfe/trunk/include/clang/Basic/SourceManager.h
>> > cfe/trunk/lib/Basic/SourceManager.cpp
>> >
>> > Modified: cfe/trunk/include/clang/Basic/SourceManager.h
>> > URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/SourceManager.h?rev=206324&r1=206323&r2=206324&view=diff
>> >
>> ==============================================================================
>> > --- cfe/trunk/include/clang/Basic/SourceManager.h (original)
>> > +++ cfe/trunk/include/clang/Basic/SourceManager.h Tue Apr 15 16:34:12
>> 2014
>> > @@ -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<ContentCache>::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.
>> > ///
>> >
>> > Modified: cfe/trunk/lib/Basic/SourceManager.cpp
>> > URL:
>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Basic/SourceManager.cpp?rev=206324&r1=206323&r2=206324&view=diff
>> >
>> ==============================================================================
>> > --- cfe/trunk/lib/Basic/SourceManager.cpp (original)
>> > +++ cfe/trunk/lib/Basic/SourceManager.cpp Tue Apr 15 16:34:12 2014
>> > @@ -436,12 +436,8 @@ SourceManager::getOrCreateContentCache(c
>> > 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<ContentCache>::Alignment;
>> > - EntryAlign = std::max(8U, EntryAlign);
>> > - Entry = ContentCacheAlloc.Allocate<ContentCache>(1, EntryAlign);
>> > + // Nope, create a new Cache entry.
>> > + Entry = ContentCacheAlloc.Allocate<ContentCache>();
>> >
>> > if (OverriddenFilesInfo) {
>> > // If the file contents are overridden with contents from another
>> file,
>> > @@ -468,12 +464,8 @@ SourceManager::getOrCreateContentCache(c
>> > /// 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<ContentCache>::Alignment;
>> > - EntryAlign = std::max(8U, EntryAlign);
>> > - ContentCache *Entry = ContentCacheAlloc.Allocate<ContentCache>(1,
>> EntryAlign);
>> > + // Add a new ContentCache to the MemBufferInfos list and return it.
>> > + ContentCache *Entry = ContentCacheAlloc.Allocate<ContentCache>();
>> > new (Entry) ContentCache();
>> > MemBufferInfos.push_back(Entry);
>> > Entry->setBuffer(Buffer);
>> >
>> >
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