diff options
author | Chris Lattner <sabre@nondot.org> | 2005-02-12 19:30:21 +0000 |
---|---|---|
committer | Chris Lattner <sabre@nondot.org> | 2005-02-12 19:30:21 +0000 |
commit | 3689a34489224a71c6306f55ce0718014c3b01cf (patch) | |
tree | 07b066633686f44dc9b53a2d9eae78b8b0cfa458 /docs/LangRef.html | |
parent | e6f8c5a71682ffcc33d3c83a40821ded8f2c8033 (diff) | |
download | external_llvm-3689a34489224a71c6306f55ce0718014c3b01cf.zip external_llvm-3689a34489224a71c6306f55ce0718014c3b01cf.tar.gz external_llvm-3689a34489224a71c6306f55ce0718014c3b01cf.tar.bz2 |
Document the newly generalized model for constant globals.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@20136 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs/LangRef.html')
-rw-r--r-- | docs/LangRef.html | 22 |
1 files changed, 16 insertions, 6 deletions
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 |