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[OMPT] Add support for ompt_event_task_dependences and…

Description

[OMPT] Add support for ompt_event_task_dependences and ompt_event_task_dependence_pair

The attached patch adds support for ompt_event_task_dependences and
ompt_event_task_dependence_pair events from the OMPT specification [1]. These
events only apply to OpenMP 4.0 and 4.1 (aka 4.5) because task dependencies
were introduced in 4.0.

With respect to the changes:

ompt_event_task_dependences
According to the specification, this event is raised after the task has been
created, thefore this event needs to be raised after ompt_event_task_begin
(in kmp_task_start). However, the dependencies are known at
kmpc_omp_task_with_deps which occurs before kmp_task_start. My modifications
extend the ompt_task_info_t struct in order to store the dependencies of the
task when _kmpc_omp_task_with_deps occurs and then they are emitted in
kmp_task_start just after raising the ompt_event_task_begin. The deps field
is allocated and valid until the event is raised and it is freed and set
to null afterwards.

ompt_event_task_dependence_pair
The processing of the dependences (i.e. checking whenever a dependence is
already satisfied) is done within kmp_process_deps. That function checks
every dependence and calls the
kmp_track_dependence routine which gives some
support for graphical output. I used that routine to emit the dependence pair
but I also needed to know the sink_task. Despite the fact that the code within
KMP_SUPPORT_GRAPH_OUTPUT refers to task_sink it may be null because
sink->dn.task (there's a comment regarding this) and in fact it does not point
to a proper pointer value because the value is set in node->dn.task = task;
after the kmp_process_deps calls in kmp_check_deps. I have extended the
kmp_process_deps and kmp_track_dependence parameter list to receive the
sink_task.

[1] https://github.com/OpenMPToolsInterface/OMPT-Technical-Report/blob/target/ompt-tr.pdf

Patch by Harald Servat
Differential Revision: http://reviews.llvm.org/D14746