Re: [PATCH] Fix result for conditional reductions matching at index 0

[Kilian Verhetsel <kilian.verhetsel@uclouvain.be>]

> This is PR81179 I think, please mention that in the changelog.

Correct, my bad for missing that.

> This unconditionally pessimizes code even if there is no valid index
> zero, right?

Almost, since for a loop such as:

  #define OFFSET 1
  unsigned int find(const unsigned int *a, unsigned int v) {
    unsigned int result = 120;
    for (unsigned int i = OFFSET; i < 32+OFFSET; i++) {
      if (a[i-OFFSET] == v) result = i;
    }
    return result;
  }

the index i will match the contents of the index vector used here ---
but this does indeed pessimize the code generated for, say, OFFSET
= 2. It is probably more sensible to use the existing code path in those
situations.

> The issue with the COND_REDUCITION index vector is overflow IIRC.

Does that mean such overflows can already manifest themselves for
regular COND_REDUCTION? I had assumed sufficient checks were already in
place because of the presence of the is_nonwrapping_integer_induction
test.