[OpenMP] Don't emit redundant zero-sized mapping nodes for overlapped structs (#148947)

The handling of overlapped structure mapping in CGOpenMPRuntime.cpp can
lead to redundant zero-sized mapping nodes at runtime. This patch fixes
it using a combination of approaches: trivially adjacent struct members
won't have a mapping node created between them, and for more complicated
cases (inheritance) the physical layout of the struct/class is used to
make sure that elements aren't missed.

I've introduced a new class to track the state whilst iterating over the
struct. This reduces a bit of redundancy in the code (accumulating
CombinedInfo both during and after the loop), which I think is a bit
neater.

Before:

omptarget --> Entry  0: Base=0x00007fff8d483830, Begin=0x00007fff8d483830, Size=48, Type=0x20, Name=unknown
omptarget --> Entry  1: Base=0x00007fff8d483830, Begin=0x00007fff8d483830, Size=0, Type=0x1000000000003, Name=unknown
omptarget --> Entry  2: Base=0x00007fff8d483830, Begin=0x00007fff8d483834, Size=0, Type=0x1000000000003, Name=unknown
omptarget --> Entry  3: Base=0x00007fff8d483830, Begin=0x00007fff8d483838, Size=0, Type=0x1000000000003, Name=unknown
omptarget --> Entry  4: Base=0x00007fff8d483830, Begin=0x00007fff8d48383c, Size=20, Type=0x1000000000003, Name=unknown
omptarget --> Entry  5: Base=0x00007fff8d483830, Begin=0x00007fff8d483854, Size=0, Type=0x1000000000003, Name=unknown
omptarget --> Entry  6: Base=0x00007fff8d483830, Begin=0x00007fff8d483858, Size=0, Type=0x1000000000003, Name=unknown
omptarget --> Entry  7: Base=0x00007fff8d483830, Begin=0x00007fff8d48385c, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry  8: Base=0x00007fff8d483830, Begin=0x00007fff8d483830, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry  9: Base=0x00007fff8d483830, Begin=0x00007fff8d483834, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry 10: Base=0x00007fff8d483830, Begin=0x00007fff8d483838, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry 11: Base=0x00007fff8d483840, Begin=0x00005e7665275130, Size=32, Type=0x1000000000013, Name=unknown
omptarget --> Entry 12: Base=0x00007fff8d483830, Begin=0x00007fff8d483850, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry 13: Base=0x00007fff8d483830, Begin=0x00007fff8d483854, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry 14: Base=0x00007fff8d483830, Begin=0x00007fff8d483858, Size=4, Type=0x1000000000003, Name=unknown

After:

omptarget --> Entry  0: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f562e0, Size=48, Type=0x20, Name=unknown
omptarget --> Entry  1: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f562ec, Size=20, Type=0x1000000000003, Name=unknown
omptarget --> Entry  2: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f5630c, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry  3: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f562e0, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry  4: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f562e4, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry  5: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f562e8, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry  6: Base=0x00007fffd0f562f0, Begin=0x000058b6013fb130, Size=32, Type=0x1000000000013, Name=unknown
omptarget --> Entry  7: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f56300, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry  8: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f56304, Size=4, Type=0x1000000000003, Name=unknown
omptarget --> Entry  9: Base=0x00007fffd0f562e0, Begin=0x00007fffd0f56308, Size=4, Type=0x1000000000003, Name=unknown

For code:

  #include <cstdlib>
  #include <cstdio>

  struct S {
    int x;
    int y;
    int z;
    int *p1;
    int *p2;
  };

  struct T : public S {
    int a;
    int b;
    int c;
  };

  int main() {
    T v;
    v.p1 = (int*) calloc(8, sizeof(int));
    v.p2 = (int*) calloc(8, sizeof(int));

  #pragma omp target map(tofrom: v, v.x, v.y, v.z, v.p1[:8], v.a, v.b, v.c)
    {
      v.x++;
      v.y += 2;
      v.z += 3;
      v.p1[0] += 4;
      v.a += 7;
      v.b += 5;
      v.c += 6;
    }

    return 0;
  }

0 files changed, 0 insertions, 0 deletions