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Introduce new linkage types linkonce_odr, weak_odr, common_odr

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and extern_weak_odr.  These are the same as the non-odr versions,
except that they indicate that the global will only be overridden
by an *equivalent* global.  In C, a function with weak linkage can
be overridden by a function which behaves completely differently.
This means that IP passes have to skip weak functions, since any
deductions made from the function definition might be wrong, since
the definition could be replaced by something completely different
at link time.   This is not allowed in C++, thanks to the ODR
(One-Definition-Rule): if a function is replaced by another at
link-time, then the new function must be the same as the original
function.  If a language knows that a function or other global can
only be overridden by an equivalent global, it can give it the
weak_odr linkage type, and the optimizers will understand that it
is alright to make deductions based on the function body.  The
code generators on the other hand map weak and weak_odr linkage
to the same thing.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@66339 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands
2009-03-07 15:45:40 +00:00
parent 0dd2a6a89f
commit 667d4b8de6
43 changed files with 370 additions and 192 deletions
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utils/vim/llvm.vim
+2 -1
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@@ -40,7 +40,8 @@ syn keyword llvmStatement extractvalue insertvalue
" Keywords.
syn keyword llvmKeyword define declare global constant
syn keyword llvmKeyword internal external
syn keyword llvmKeyword linkonce weak appending common extern_weak
syn keyword llvmKeyword linkonce linkonce_odr weak weak_odr appending
syn keyword llvmKeyword common common_odr extern_weak extern_weak_odr
syn keyword llvmKeyword thread_local dllimport dllexport
syn keyword llvmKeyword hidden protected default
syn keyword llvmKeyword except deplibs