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 <a name="OpenMP"></a>
 <div class="header">
 <p>
 Previous: <a href="Cleanups.html#Cleanups" accesskey="p" rel="prev">Cleanups</a>, Up: <a href="Statements.html#Statements" accesskey="u" rel="up">Statements</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
 </div>
 <hr>
 <a name="OpenMP-1"></a>
 <h4 class="subsection">10.7.7 OpenMP</h4>
 <a name="index-OMP_005fPARALLEL"></a>
 <a name="index-OMP_005fFOR"></a>
 <a name="index-OMP_005fSECTIONS"></a>
 <a name="index-OMP_005fSINGLE"></a>
 <a name="index-OMP_005fSECTION"></a>
 <a name="index-OMP_005fMASTER"></a>
 <a name="index-OMP_005fORDERED"></a>
 <a name="index-OMP_005fCRITICAL"></a>
 <a name="index-OMP_005fRETURN"></a>
 <a name="index-OMP_005fCONTINUE"></a>
 <a name="index-OMP_005fATOMIC"></a>
 <a name="index-OMP_005fCLAUSE"></a>

 <p>All the statements starting with <code>OMP_</code> represent directives and
 clauses used by the OpenMP API <a href="http://www.openmp.org/">http://www.openmp.org/</a><!-- /@w -->.
 </p>
 <dl compact="compact">
 <dt><code>OMP_PARALLEL</code></dt>
 <dd>
 <p>Represents <code>#pragma omp parallel [clause1 &hellip; clauseN]</code>. It
 has four operands:
 </p>
 <p>Operand <code>OMP_PARALLEL_BODY</code> is valid while in GENERIC and
 High GIMPLE forms.  It contains the body of code to be executed
 by all the threads.  During GIMPLE lowering, this operand becomes
 <code>NULL</code> and the body is emitted linearly after
 <code>OMP_PARALLEL</code>.
 </p>
 <p>Operand <code>OMP_PARALLEL_CLAUSES</code> is the list of clauses
 associated with the directive.
 </p>
 <p>Operand <code>OMP_PARALLEL_FN</code> is created by
 <code>pass_lower_omp</code>, it contains the <code>FUNCTION_DECL</code>
 for the function that will contain the body of the parallel
 region.
 </p>
 <p>Operand <code>OMP_PARALLEL_DATA_ARG</code> is also created by
 <code>pass_lower_omp</code>. If there are shared variables to be
 communicated to the children threads, this operand will contain
 the <code>VAR_DECL</code> that contains all the shared values and
 variables.
 </p>
 </dd>
 <dt><code>OMP_FOR</code></dt>
 <dd>
 <p>Represents <code>#pragma omp for [clause1 &hellip; clauseN]</code>.  It
 has 5 operands:
 </p>
 <p>Operand <code>OMP_FOR_BODY</code> contains the loop body.
 </p>
 <p>Operand <code>OMP_FOR_CLAUSES</code> is the list of clauses
 associated with the directive.
 </p>
 <p>Operand <code>OMP_FOR_INIT</code> is the loop initialization code of
 the form <code>VAR = N1</code>.
 </p>
 <p>Operand <code>OMP_FOR_COND</code> is the loop conditional expression
 of the form <code>VAR {&lt;,&gt;,&lt;=,&gt;=} N2</code>.
 </p>
 <p>Operand <code>OMP_FOR_INCR</code> is the loop index increment of the
 form <code>VAR {+=,-=} INCR</code>.
 </p>
 <p>Operand <code>OMP_FOR_PRE_BODY</code> contains side-effect code from
 operands <code>OMP_FOR_INIT</code>, <code>OMP_FOR_COND</code> and
 <code>OMP_FOR_INC</code>.  These side-effects are part of the
 <code>OMP_FOR</code> block but must be evaluated before the start of
 loop body.
 </p>
 <p>The loop index variable <code>VAR</code> must be a signed integer variable,
 which is implicitly private to each thread.  Bounds
 <code>N1</code> and <code>N2</code> and the increment expression
 <code>INCR</code> are required to be loop invariant integer
 expressions that are evaluated without any synchronization. The
 evaluation order, frequency of evaluation and side-effects are
 unspecified by the standard.
 </p>
 </dd>
 <dt><code>OMP_SECTIONS</code></dt>
 <dd>
 <p>Represents <code>#pragma omp sections [clause1 &hellip; clauseN]</code>.
 </p>
 <p>Operand <code>OMP_SECTIONS_BODY</code> contains the sections body,
 which in turn contains a set of <code>OMP_SECTION</code> nodes for
 each of the concurrent sections delimited by <code>#pragma omp
 section</code>.
 </p>
 <p>Operand <code>OMP_SECTIONS_CLAUSES</code> is the list of clauses
 associated with the directive.
 </p>
 </dd>
 <dt><code>OMP_SECTION</code></dt>
 <dd>
 <p>Section delimiter for <code>OMP_SECTIONS</code>.
 </p>
 </dd>
 <dt><code>OMP_SINGLE</code></dt>
 <dd>
 <p>Represents <code>#pragma omp single</code>.
 </p>
 <p>Operand <code>OMP_SINGLE_BODY</code> contains the body of code to be
 executed by a single thread.
 </p>
 <p>Operand <code>OMP_SINGLE_CLAUSES</code> is the list of clauses
 associated with the directive.
 </p>
 </dd>
 <dt><code>OMP_MASTER</code></dt>
 <dd>
 <p>Represents <code>#pragma omp master</code>.
 </p>
 <p>Operand <code>OMP_MASTER_BODY</code> contains the body of code to be
 executed by the master thread.
 </p>
 </dd>
 <dt><code>OMP_ORDERED</code></dt>
 <dd>
 <p>Represents <code>#pragma omp ordered</code>.
 </p>
 <p>Operand <code>OMP_ORDERED_BODY</code> contains the body of code to be
 executed in the sequential order dictated by the loop index
 variable.
 </p>
 </dd>
 <dt><code>OMP_CRITICAL</code></dt>
 <dd>
 <p>Represents <code>#pragma omp critical [name]</code>.
 </p>
 <p>Operand <code>OMP_CRITICAL_BODY</code> is the critical section.
 </p>
 <p>Operand <code>OMP_CRITICAL_NAME</code> is an optional identifier to
 label the critical section.
 </p>
 </dd>
 <dt><code>OMP_RETURN</code></dt>
 <dd>
 <p>This does not represent any OpenMP directive, it is an artificial
 marker to indicate the end of the body of an OpenMP. It is used
 by the flow graph (<code>tree-cfg.c</code>) and OpenMP region
 building code (<code>omp-low.c</code>).
 </p>
 </dd>
 <dt><code>OMP_CONTINUE</code></dt>
 <dd>
 <p>Similarly, this instruction does not represent an OpenMP
 directive, it is used by <code>OMP_FOR</code> and
 <code>OMP_SECTIONS</code> to mark the place where the code needs to
 loop to the next iteration (in the case of <code>OMP_FOR</code>) or
 the next section (in the case of <code>OMP_SECTIONS</code>).
 </p>
 <p>In some cases, <code>OMP_CONTINUE</code> is placed right before
 <code>OMP_RETURN</code>.  But if there are cleanups that need to
 occur right after the looping body, it will be emitted between
 <code>OMP_CONTINUE</code> and <code>OMP_RETURN</code>.
 </p>
 </dd>
 <dt><code>OMP_ATOMIC</code></dt>
 <dd>
 <p>Represents <code>#pragma omp atomic</code>.
 </p>
 <p>Operand 0 is the address at which the atomic operation is to be
 performed.
 </p>
 <p>Operand 1 is the expression to evaluate.  The gimplifier tries
 three alternative code generation strategies.  Whenever possible,
 an atomic update built-in is used.  If that fails, a
 compare-and-swap loop is attempted.  If that also fails, a
 regular critical section around the expression is used.
 </p>
 </dd>
 <dt><code>OMP_CLAUSE</code></dt>
 <dd>
 <p>Represents clauses associated with one of the <code>OMP_</code> directives.
 Clauses are represented by separate subcodes defined in
 <samp>tree.h</samp>.  Clauses codes can be one of:
 <code>OMP_CLAUSE_PRIVATE</code>, <code>OMP_CLAUSE_SHARED</code>,
 <code>OMP_CLAUSE_FIRSTPRIVATE</code>,
 <code>OMP_CLAUSE_LASTPRIVATE</code>, <code>OMP_CLAUSE_COPYIN</code>,
 <code>OMP_CLAUSE_COPYPRIVATE</code>, <code>OMP_CLAUSE_IF</code>,
 <code>OMP_CLAUSE_NUM_THREADS</code>, <code>OMP_CLAUSE_SCHEDULE</code>,
 <code>OMP_CLAUSE_NOWAIT</code>, <code>OMP_CLAUSE_ORDERED</code>,
 <code>OMP_CLAUSE_DEFAULT</code>, <code>OMP_CLAUSE_REDUCTION</code>,
 <code>OMP_CLAUSE_COLLAPSE</code>, <code>OMP_CLAUSE_UNTIED</code>,
 <code>OMP_CLAUSE_FINAL</code>, and <code>OMP_CLAUSE_MERGEABLE</code>.  Each code
 represents the corresponding OpenMP clause.
 </p>
 <p>Clauses associated with the same directive are chained together
 via <code>OMP_CLAUSE_CHAIN</code>. Those clauses that accept a list
 of variables are restricted to exactly one, accessed with
 <code>OMP_CLAUSE_VAR</code>.  Therefore, multiple variables under the
 same clause <code>C</code> need to be represented as multiple <code>C</code> clauses
 chained together.  This facilitates adding new clauses during
 compilation.
 </p>
 </dd>
 </dl>


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	<a name="OpenMP"></a>
	<div class="header">
	<p>
	Previous: <a href="Cleanups.html#Cleanups" accesskey="p" rel="prev">Cleanups</a>, Up: <a href="Statements.html#Statements" accesskey="u" rel="up">Statements</a>   [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
	</div>
	<hr>
	<a name="OpenMP-1"></a>
	<h4 class="subsection">10.7.7 OpenMP</h4>
	<a name="index-OMP_005fPARALLEL"></a>
	<a name="index-OMP_005fFOR"></a>
	<a name="index-OMP_005fSECTIONS"></a>
	<a name="index-OMP_005fSINGLE"></a>
	<a name="index-OMP_005fSECTION"></a>
	<a name="index-OMP_005fMASTER"></a>
	<a name="index-OMP_005fORDERED"></a>
	<a name="index-OMP_005fCRITICAL"></a>
	<a name="index-OMP_005fRETURN"></a>
	<a name="index-OMP_005fCONTINUE"></a>
	<a name="index-OMP_005fATOMIC"></a>
	<a name="index-OMP_005fCLAUSE"></a>

	<p>All the statements starting with <code>OMP_</code> represent directives and
	clauses used by the OpenMP API <a href="http://www.openmp.org/">http://www.openmp.org/</a><!-- /@w -->.
	</p>
	<dl compact="compact">
	<dt><code>OMP_PARALLEL</code></dt>
	<dd>
	<p>Represents <code>#pragma omp parallel [clause1 … clauseN]</code>. It
	has four operands:
	</p>
	<p>Operand <code>OMP_PARALLEL_BODY</code> is valid while in GENERIC and
	High GIMPLE forms. It contains the body of code to be executed
	by all the threads. During GIMPLE lowering, this operand becomes
	<code>NULL</code> and the body is emitted linearly after
	<code>OMP_PARALLEL</code>.
	</p>
	<p>Operand <code>OMP_PARALLEL_CLAUSES</code> is the list of clauses
	associated with the directive.
	</p>
	<p>Operand <code>OMP_PARALLEL_FN</code> is created by
	<code>pass_lower_omp</code>, it contains the <code>FUNCTION_DECL</code>
	for the function that will contain the body of the parallel
	region.
	</p>
	<p>Operand <code>OMP_PARALLEL_DATA_ARG</code> is also created by
	<code>pass_lower_omp</code>. If there are shared variables to be
	communicated to the children threads, this operand will contain
	the <code>VAR_DECL</code> that contains all the shared values and
	variables.
	</p>
	</dd>
	<dt><code>OMP_FOR</code></dt>
	<dd>
	<p>Represents <code>#pragma omp for [clause1 … clauseN]</code>. It
	has 5 operands:
	</p>
	<p>Operand <code>OMP_FOR_BODY</code> contains the loop body.
	</p>
	<p>Operand <code>OMP_FOR_CLAUSES</code> is the list of clauses
	associated with the directive.
	</p>
	<p>Operand <code>OMP_FOR_INIT</code> is the loop initialization code of
	the form <code>VAR = N1</code>.
	</p>
	<p>Operand <code>OMP_FOR_COND</code> is the loop conditional expression
	of the form <code>VAR {<,>,<=,>=} N2</code>.
	</p>
	<p>Operand <code>OMP_FOR_INCR</code> is the loop index increment of the
	form <code>VAR {+=,-=} INCR</code>.
	</p>
	<p>Operand <code>OMP_FOR_PRE_BODY</code> contains side-effect code from
	operands <code>OMP_FOR_INIT</code>, <code>OMP_FOR_COND</code> and
	<code>OMP_FOR_INC</code>. These side-effects are part of the
	<code>OMP_FOR</code> block but must be evaluated before the start of
	loop body.
	</p>
	<p>The loop index variable <code>VAR</code> must be a signed integer variable,
	which is implicitly private to each thread. Bounds
	<code>N1</code> and <code>N2</code> and the increment expression
	<code>INCR</code> are required to be loop invariant integer
	expressions that are evaluated without any synchronization. The
	evaluation order, frequency of evaluation and side-effects are
	unspecified by the standard.
	</p>
	</dd>
	<dt><code>OMP_SECTIONS</code></dt>
	<dd>
	<p>Represents <code>#pragma omp sections [clause1 … clauseN]</code>.
	</p>
	<p>Operand <code>OMP_SECTIONS_BODY</code> contains the sections body,
	which in turn contains a set of <code>OMP_SECTION</code> nodes for
	each of the concurrent sections delimited by <code>#pragma omp
	section</code>.
	</p>
	<p>Operand <code>OMP_SECTIONS_CLAUSES</code> is the list of clauses
	associated with the directive.
	</p>
	</dd>
	<dt><code>OMP_SECTION</code></dt>
	<dd>
	<p>Section delimiter for <code>OMP_SECTIONS</code>.
	</p>
	</dd>
	<dt><code>OMP_SINGLE</code></dt>
	<dd>
	<p>Represents <code>#pragma omp single</code>.
	</p>
	<p>Operand <code>OMP_SINGLE_BODY</code> contains the body of code to be
	executed by a single thread.
	</p>
	<p>Operand <code>OMP_SINGLE_CLAUSES</code> is the list of clauses
	associated with the directive.
	</p>
	</dd>
	<dt><code>OMP_MASTER</code></dt>
	<dd>
	<p>Represents <code>#pragma omp master</code>.
	</p>
	<p>Operand <code>OMP_MASTER_BODY</code> contains the body of code to be
	executed by the master thread.
	</p>
	</dd>
	<dt><code>OMP_ORDERED</code></dt>
	<dd>
	<p>Represents <code>#pragma omp ordered</code>.
	</p>
	<p>Operand <code>OMP_ORDERED_BODY</code> contains the body of code to be
	executed in the sequential order dictated by the loop index
	variable.
	</p>
	</dd>
	<dt><code>OMP_CRITICAL</code></dt>
	<dd>
	<p>Represents <code>#pragma omp critical [name]</code>.
	</p>
	<p>Operand <code>OMP_CRITICAL_BODY</code> is the critical section.
	</p>
	<p>Operand <code>OMP_CRITICAL_NAME</code> is an optional identifier to
	label the critical section.
	</p>
	</dd>
	<dt><code>OMP_RETURN</code></dt>
	<dd>
	<p>This does not represent any OpenMP directive, it is an artificial
	marker to indicate the end of the body of an OpenMP. It is used
	by the flow graph (<code>tree-cfg.c</code>) and OpenMP region
	building code (<code>omp-low.c</code>).
	</p>
	</dd>
	<dt><code>OMP_CONTINUE</code></dt>
	<dd>
	<p>Similarly, this instruction does not represent an OpenMP
	directive, it is used by <code>OMP_FOR</code> and
	<code>OMP_SECTIONS</code> to mark the place where the code needs to
	loop to the next iteration (in the case of <code>OMP_FOR</code>) or
	the next section (in the case of <code>OMP_SECTIONS</code>).
	</p>
	<p>In some cases, <code>OMP_CONTINUE</code> is placed right before
	<code>OMP_RETURN</code>. But if there are cleanups that need to
	occur right after the looping body, it will be emitted between
	<code>OMP_CONTINUE</code> and <code>OMP_RETURN</code>.
	</p>
	</dd>
	<dt><code>OMP_ATOMIC</code></dt>
	<dd>
	<p>Represents <code>#pragma omp atomic</code>.
	</p>
	<p>Operand 0 is the address at which the atomic operation is to be
	performed.
	</p>
	<p>Operand 1 is the expression to evaluate. The gimplifier tries
	three alternative code generation strategies. Whenever possible,
	an atomic update built-in is used. If that fails, a
	compare-and-swap loop is attempted. If that also fails, a
	regular critical section around the expression is used.
	</p>
	</dd>
	<dt><code>OMP_CLAUSE</code></dt>
	<dd>
	<p>Represents clauses associated with one of the <code>OMP_</code> directives.
	Clauses are represented by separate subcodes defined in
	<samp>tree.h</samp>. Clauses codes can be one of:
	<code>OMP_CLAUSE_PRIVATE</code>, <code>OMP_CLAUSE_SHARED</code>,
	<code>OMP_CLAUSE_FIRSTPRIVATE</code>,
	<code>OMP_CLAUSE_LASTPRIVATE</code>, <code>OMP_CLAUSE_COPYIN</code>,
	<code>OMP_CLAUSE_COPYPRIVATE</code>, <code>OMP_CLAUSE_IF</code>,
	<code>OMP_CLAUSE_NUM_THREADS</code>, <code>OMP_CLAUSE_SCHEDULE</code>,
	<code>OMP_CLAUSE_NOWAIT</code>, <code>OMP_CLAUSE_ORDERED</code>,
	<code>OMP_CLAUSE_DEFAULT</code>, <code>OMP_CLAUSE_REDUCTION</code>,
	<code>OMP_CLAUSE_COLLAPSE</code>, <code>OMP_CLAUSE_UNTIED</code>,
	<code>OMP_CLAUSE_FINAL</code>, and <code>OMP_CLAUSE_MERGEABLE</code>. Each code
	represents the corresponding OpenMP clause.
	</p>
	<p>Clauses associated with the same directive are chained together
	via <code>OMP_CLAUSE_CHAIN</code>. Those clauses that accept a list
	of variables are restricted to exactly one, accessed with
	<code>OMP_CLAUSE_VAR</code>. Therefore, multiple variables under the
	same clause <code>C</code> need to be represented as multiple <code>C</code> clauses
	chained together. This facilitates adding new clauses during
	compilation.
	</p>
	</dd>
	</dl>


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