[clang] [llvm] [openmp] [CLANG][OpenMP] Restore loop variable values after transformation directives (PR #214717)

[Zahira Ammarguellat via cfe-commits]

zahiraam wrote:

> Check these tests:
> 
> ```
> #include <stdio.h>
> #include <stdlib.h>
> int main() {
>   int i, j, k;
>   int count = 0;
> #pragma omp fuse looprange(1, 2)
>   {
>     for (i = 0; i < 10; i++)
>       ;
>     for (j = 0; j < 15; j++)
>       ;
>     // Reads i: must observe the loop-exit value 10, not the value left by
>     // the last fused iteration (9).
>     for (k = 0; k < i; k++)
>       count++;
>   }
>   printf("count=%d i=%d j=%d k=%d\n", count, i, j, k);
>   return EXIT_SUCCESS;
> }
> ```
> 
> ```
> #include <stdio.h>
> #include <stdlib.h>
> int main() {
>   int i, j, l;
> #pragma omp fuse
>   {
> #pragma omp fuse
>     {
>       for (i = 0; i < 10; i++)
>         ;
>       for (j = 0; j < 20; j++)
>         ;
>     }
>     for (l = 0; l < 5; l++)
>       ;
>   }
>   printf("i=%d j=%d l=%d\n", i, j, l);
>   return EXIT_SUCCESS;
> }
> ```
> 
> ```
> 
> #include <stdio.h>
> #include <stdlib.h>
> int main() {
>   int i, j, k, l;
> #pragma omp fuse looprange(2, 2)
>   {
> #pragma omp fuse looprange(2, 2)
>     {
>       for (i = 0; i < 8; i++)
>         ;
>       for (j = 0; j < 16; j++)
>         ;
>       for (k = 0; k < 32; k++)
>         ;
>     }
>     for (l = 0; l < 4; l++)
>       ;
>   }
>   printf("i=%d j=%d k=%d l=%d\n", i, j, k, l);
>   return EXIT_SUCCESS;
> }
> ```

With the new commit, these tests are generating the correct values.

https://github.com/llvm/llvm-project/pull/214717