Certain tile sizes trigger an assertion

[sebastiankreutzer]

When using user-directed tiling, for certain tile sizes, the following assertion is triggered:

/home/sebastian/git/llvm-project-sollve/polly/lib/External/isl/isl_aff.c:8169: cannot extract range space from empty input

This seems to occur when both

• The trip count is a compile time constant
• For every loop, the trip count is a multiple of the chosen tile size

Consider the following code:

#define N 64
#define M 32

void foo(float* __restrict__ a, float* __restrict__  b, float* __restrict__ c) {
#pragma clang loop(i, j) tile sizes(32, 16) floor_ids(i1, j1) tile_ids(i2, j1) peel(rectangular)
#pragma clang loop id(i)
  for (int i = 0; i < N; i++) {
#pragma clang loop id(j)
    for (int j = 0; j < M; j++) {
        c[i] += a[i*N+j] * b[j];
    }
  }
}

For the given tile sizes (32, 16), compilation will fail.
On the other hand, tile sizes such as (5, 16), (32, 5), where the trip count is not divisible by each size, work fine.

Here's the full stack trace.

[sebastiankreutzer]

I should add that this only occurs when rectangular peeling is specified.