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clarify comment, this is undefined behavior in any case, even if it only

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bits VC++ right now.

llvm-svn: 47565
This commit is contained in:
Chris Lattner 2008-02-25 21:38:21 +00:00
parent 3ed28de5cc
commit f5c619f98c
1 changed files with 10 additions and 30 deletions
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40
clang/Lex/HeaderSearch.cpp
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@ -228,22 +228,12 @@ const FileEntry *HeaderSearch::LookupFile(const char *FilenameStart,
if (const FileEntry *FE = FileMgr.getFile(TmpDir.begin(), TmpDir.end())) {
// Leave CurDir unset.
// This file is a system header or C++ unfriendly if the old file is.
// Note: Don't use:
//
// getFileInfo(FE).DirInfo = getFileInfo(CurFileEnt).DirInfo;
//
// MSVC, behind the scenes, does this:
//
// PerFileInfo &pf1 = getFileInfo(CurFileEnt);
// PerFileInfo &pf2 = getFileInfo(FE);
// pf2.DirInfo = pf1.DirInfo
//
// The problem is that if there's a resize() of the FileInfo vector during
// the getFileInfo(FE) call, pf1 will point to invalid data. To fix
// this problem, make the assignment through a temporary.
unsigned int tmp = getFileInfo(CurFileEnt).DirInfo;
getFileInfo(FE).DirInfo = tmp;
// Note that the temporary 'DirInfo' is required here, as either call to
// getFileInfo could resize the vector and we don't want to rely on order
// of evaluation.
unsigned DirInfo = getFileInfo(CurFileEnt).DirInfo;
getFileInfo(FE).DirInfo = DirInfo;
return FE;
}
}
@ -372,22 +362,12 @@ LookupSubframeworkHeader(const char *FilenameStart,
}
// This file is a system header or C++ unfriendly if the old file is.
// Note: Don't use:
//
// getFileInfo(FE).DirInfo = getFileInfo(ContextFileEnt).DirInfo;
//
// MSVC, behind the scenes, does this:
//
// PerFileInfo &pf1 = getFileInfo(ContextFileEnt);
// PerFileInfo &pf2 = getFileInfo(FE);
// pf2.DirInfo = pf1.DirInfo
//
// The problem is that if there's a resize() of the FileInfo vector during
// the getFileInfo(FE) call, pf1 will point to invalid data. The solution
// is to make the assignment through a temporary.
unsigned int tmp = getFileInfo(ContextFileEnt).DirInfo;
getFileInfo(FE).DirInfo = tmp;
// Note that the temporary 'DirInfo' is required here, as either call to
// getFileInfo could resize the vector and we don't want to rely on order
// of evaluation.
unsigned DirInfo = getFileInfo(ContextFileEnt).DirInfo;
getFileInfo(FE).DirInfo = DirInfo;
return FE;
}