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Document the newly generalized model for constant globals.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20136 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2005-02-12 19:30:21 +00:00
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docs/LangRef.html
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@ -423,12 +423,22 @@ to have any linkage type other than "externally visible".</a></p>
<div class="doc_text">
<p>Global variables define regions of memory allocated at compilation
time instead of run-time. Global variables may optionally be
initialized. A variable may be defined as a global "constant", which
indicates that the contents of the variable will never be modified
(enabling better optimization, allowing the global data to be placed in the
read-only section of an executable, etc).</p>
<p>Global variables define regions of memory allocated at compilation time
instead of run-time. Global variables may optionally be initialized. A
variable may be defined as a global "constant", which indicates that the
contents of the variable will <b>never</b> be modified (enabling better
optimization, allowing the global data to be placed in the read-only section of
an executable, etc). Note that variables that need runtime initialization
cannot be marked "constant", as there is a store to the variable.</p>
<p>
LLVM explicitly allows <em>declarations</em> of global variables to be marked
constant, even if the final definition of the global is not. This capability
can be used to enable slightly better optimization of the program, but requires
the language definition to guarantee that optimizations based on the
'constantness' are valid for the translation units that do not include the
definition.
</p>
<p>As SSA values, global variables define pointer values that are in
scope (i.e. they dominate) all basic blocks in the program. Global