Created attachment 54497 [details]
Assembly code generated by test case

Looking a bit more at the code generated for the test code of PR108839.

For the test
$ cat u2.c
void foo(double *const restrict dx, double *dy, double da, long int n)
{
      long int m = n % 4;
      for (unsigned long i = 0; i < m; i++ )
        dy[i] = dy[i] + da * dx[i];
}

a recently-ish trunk gives, with

$ gcc -S -O3  -funroll-all-loops -fno-tree-vectorize u2.c

far too much unrolling for a loop which can only be executed, at
most, four times (see attachment).

The range information about m does not appear to be propagated to
the unroll passes.