[PATCH] D39136: [OpenMP] Avoid VLAs for some reductions on array sections

[Jonas Hahnfeld via Phabricator via cfe-commits]

Hahnfeld created this revision.

In some cases the compiler can deduce the length of an array section
as constants. With this information, VLAs can be avoided in place of
a constant sized array or even a scalar value if the length is 1.
Example:

  int a[4], b[2];
  pragma omp parallel reduction(+: a[1:2], b[1:1])
  { }

For chained array sections, this optimization is restricted to cases
where all array sections except the last have a constant length 1.
This trivially guarantees that there are no holes in the memory region
that needs to be privatized.
Example:

  int c[3][4];
  pragma omp parallel reduction(+: c[1:1][1:2])
  { }


https://reviews.llvm.org/D39136

Files:
  lib/CodeGen/CGOpenMPRuntime.cpp
  lib/CodeGen/CGStmtOpenMP.cpp
  lib/Sema/SemaOpenMP.cpp
  test/OpenMP/for_reduction_codegen.cpp
  test/OpenMP/for_reduction_codegen_UDR.cpp

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