[OpenMP] Implement printing TDGs to dot files

[Munesanz]

Summary

This patch implements the "__kmp_print_tdg_dot" function, that prints a task dependency graph into a dot file containing the tasks and their dependencies.

It is activated through a new environment variable "KMP_TDG_DOT"

[josemonsalve2]

openmp/runtime/src/kmp_tasking.cpp

5482–5483

Just a suggestion.

[tlwilmar]

I think OMP_ prefix is reserved for environment variables defined by the spec, no? Or is this being added to the spec?

[josemonsalve2]

In D150962#4356578, @tlwilmar wrote:

I think OMP_ prefix is reserved for environment variables defined by the spec, no? Or is this being added to the spec?

This is a good point. This was introduced in a previous patch. We can consider renaming. What do you think @jdoerfert @tianshilei1992? OMPX_ or LIBOMP_?

[Munesanz]

Rename "OMP_TDG_DOT" to "KMP_TDG_DOT" and refactor printing.

[tianshilei1992]

Yeah, KMP is good.

[josemonsalve2]

Ping.

[tianshilei1992]

LG but you might want to get a test case.

[josemonsalve2]

@Munesanz once you add that test case, I will land it.

[Munesanz]

Added test

[tianshilei1992]

openmp/runtime/test/tasking/omp_record_replay_print_dot.cpp

74

it might be better to use FileCheck here.

[Munesanz]

Rebase