linkage: this linkage type only applies to declarations,
but ODR is only relevant to globals with definitions.
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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.
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the section or the visibility from one global
value to another: copyAttributesFrom. This is
particularly useful for duplicating functions:
previously this was done by explicitly copying
each attribute in turn at each place where a
new function was created out of an old one, with
the result that obscure attributes were regularly
forgotten (like the collector or the section).
Hopefully now everything is uniform and nothing
is forgotten.
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are represented as "weak", but there are subtle differences
in some cases on Darwin, so we need both. The intent
is that "common" will behave identically to "weak" unless
somebody changes their target to do something else.
No functional change as yet.
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_sabre_: it has a major problem: by the time ~Value is run, all of the "parts" of the derived classes have been destroyed
_sabre_: the vtable lives to fight another day
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better, gives the compiler a chance to validate the cast and reduces warnings
if the user turns on -Wold-style-cast option.
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field into SubclassData in Value. This shrinks GlobalVAlue from 48->40
bytes, Function from 88->76, and GlobalVariable from 76->68. This trims
4640 bytes off my testcase, reading a bc file without materializing any
functions.
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exprs hanging off a global, even if the global is not otherwise dead. This
requires some tricky iterator gymnastics.
This implements Transforms/GlobalOpt/constantexpr-dangle.ll by deleting a
constantexpr that made it appear that the address of the function was taken.
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as its main datastructure. There are many improvements yet to be made, but
this speeds up opt --std-compile-opts on 447.dealII by 7.3%.
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* PIC-aware internal structures in X86 Codegen have been refactored
* Visibility (default/weak) has been added
* Docs fixes (external weak linkage, visibility, formatting)
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DLL* linkages got full (I hope) codegeneration support in C & both x86
assembler backends.
External weak linkage added for future use, we don't provide any
codegeneration, etc. support for it.
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