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<title>GNU Compiler Collection (GCC) Internals: Cilk Plus Transformation</title>

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<a name="Cilk-Plus-Transformation"></a>
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<a name="Cilk-Plus-Transformation-1"></a>
<h3 class="section">9.2 Cilk Plus Transformation</h3>
<a name="index-CILK_005fPLUS"></a>

<p>If Cilk Plus generation (flag <samp>-fcilkplus</samp>) is enabled, all the Cilk 
Plus code is transformed into equivalent C and C++ functions.  Majority of this 
transformation occurs toward the end of the parsing and right before the 
gimplification pass.  
</p>
<p>These are the major components to the Cilk Plus language extension:
</p><ul>
<li> Array Notations:
During parsing phase, all the array notation specific information is stored in 
<code>ARRAY_NOTATION_REF</code> tree using the function 
<code>c_parser_array_notation</code>.  During the end of parsing, we check the entire
function to see if there are any array notation specific code (using the 
function <code>contains_array_notation_expr</code>).  If this function returns 
true, then we expand them using either <code>expand_array_notation_exprs</code> or
<code>build_array_notation_expr</code>.  For the cases where array notations are 
inside conditions, they are transformed using the function 
<code>fix_conditional_array_notations</code>.  The C language-specific routines are 
located in <samp>c/c-array-notation.c</samp> and the equivalent C++ routines are in 
the file <samp>cp/cp-array-notation.c</samp>.  Common routines such as functions to 
initialize built-in functions are stored in <samp>array-notation-common.c</samp>.

</li><li> Cilk keywords:
<ul>
<li> <code>_Cilk_spawn</code>:
The <code>_Cilk_spawn</code> keyword is parsed and the function it contains is marked 
as a spawning function.  The spawning function is called the spawner.  At 
the end of the parsing phase, appropriate built-in functions are 
added to the spawner that are defined in the Cilk runtime.  The appropriate 
locations of these functions, and the internal structures are detailed in 
<code>cilk_init_builtins</code> in the file <samp>cilk-common.c</samp>.  The pointers to 
Cilk functions and fields of internal structures are described 
in <samp>cilk.h</samp>.  The built-in functions are described in 
<samp>cilk-builtins.def</samp>.

<p>During gimplification, a new &quot;spawn-helper&quot; function is created.  
The spawned function is replaced with a spawn helper function in the spawner.  
The spawned function-call is moved into the spawn helper.  The main function
that does these transformations is <code>gimplify_cilk_spawn</code> in
<samp>c-family/cilk.c</samp>.  In the spawn-helper, the gimplification function 
<code>gimplify_call_expr</code>, inserts a function call <code>__cilkrts_detach</code>.
This function is expanded by <code>builtin_expand_cilk_detach</code> located in
<samp>c-family/cilk.c</samp>.
</p>
</li><li> <code>_Cilk_sync</code>:
<code>_Cilk_sync</code> is parsed like a keyword.  During gimplification, 
the function <code>gimplify_cilk_sync</code> in <samp>c-family/cilk.c</samp>, will replace
this keyword with a set of functions that are stored in the Cilk runtime.  
One of the internal functions inserted during gimplification, 
<code>__cilkrts_pop_frame</code> must be expanded by the compiler and is 
done by <code>builtin_expand_cilk_pop_frame</code> in <samp>cilk-common.c</samp>.

</li></ul>
</li></ul>

<p>Documentation about Cilk Plus and language specification is provided under the
&quot;Learn&quot; section in <a href="https://www.cilkplus.org">https://www.cilkplus.org</a><!-- /@w -->.  It is worth mentioning
that the current implementation follows ABI 1.1.
</p>
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