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| -rw-r--r-- | docs/LangRef.html | 22 |
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diff --git a/docs/LangRef.html b/docs/LangRef.html index e4e2d44..2ad6828 100644 --- a/docs/LangRef.html +++ b/docs/LangRef.html @@ -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 |