On Mon, Aug 1, 2016 at 11:24 AM, Alan Hayward <alan.hayw...@arm.com> wrote:
> In the given test case, the loop is split into vectorised and non
> vectorised
> versions due to peeling. At the end of the loop the IVs are incremented to
> their latest value. This is achieved by taking the base of the loop (g_21)
> and
> adding the iterations (240) multiplied by the step (_6):
>
> <bb 15>:
> # _106 = PHI <_6(12)>
> _84 = _106 * 240;
> _85 = (char) _84;
> tmp.19_83 = g_21(D) + _85;
>
> However, the step (_6) varies within the loop and therefore the
> calculation is
> incorrect.
>
> This patch fixes the error by disallowing vectorization if the step of the
> IV
> is not an invariant within the loop.
>
> Also added debug comment for when the optimisation fails due to chrec.
>
> Tested on x86.
>
> Ok to commit?
Ok.
To fix this we'd have to vectorize the induction variable itself, correct?
Richard.
> Alan.
>
>
> gcc/
> PR tree-optimization/71818
> * tree-vect-loop-manip.c (vect_can_advance_ivs_p): Don't advance IVs
> with non invariant evolutions
>
> testsuite/
> PR tree-optimization/71818
> * gcc.dg/vect/pr71818.c: New
>
>
>
>
>
> diff --git a/gcc/testsuite/gcc.dg/vect/pr71818.c
> b/gcc/testsuite/gcc.dg/vect/pr71818.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..2946551f8bb8c552565c2e79b16359ca3
> 9d13ed6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/pr71818.c
> @@ -0,0 +1,16 @@
> +/* { dg-do compile } */
> +
> +char a;
> +short b;
> +int c, d;
> +void fn1() {
> + char e = 75, g;
> + unsigned char *f = &e;
> + a = 21;
> + for (; a <= 48; a++) {
> + for (; e <= 6;)
> + ;
> + g -= e -= b || g <= c;
> + }
> + d = *f;
> +}
> diff --git a/gcc/tree-vect-loop-manip.c b/gcc/tree-vect-loop-manip.c
> index
> 819abcda81a25c4ed25749c29b357110fca647d2..4d68f7143e1117085aae8d2168ed1425e
> 7e6aa08 100644
> --- a/gcc/tree-vect-loop-manip.c
> +++ b/gcc/tree-vect-loop-manip.c
> @@ -40,6 +40,7 @@ along with GCC; see the file COPYING3. If not see
> #include "cfgloop.h"
> #include "tree-scalar-evolution.h"
> #include "tree-vectorizer.h"
> +#include "tree-ssa-loop-ivopts.h"
>
> /*************************************************************************
> Simple Loop Peeling Utilities
> @@ -1592,10 +1593,26 @@ vect_can_advance_ivs_p (loop_vec_info loop_vinfo)
> }
>
> /* FORNOW: We do not transform initial conditions of IVs
> + which evolution functions are not invariants in the loop. */
> +
> + if (!expr_invariant_in_loop_p (loop, evolution_part))
> + {
> + if (dump_enabled_p ())
> + dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> + "evolution not invariant in loop.\n");
> + return false;
> + }
> +
> + /* FORNOW: We do not transform initial conditions of IVs
> which evolution functions are a polynomial of degree >= 2. */
>
> if (tree_is_chrec (evolution_part))
> - return false;
> + {
> + if (dump_enabled_p ())
> + dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> + "evolution is chrec.\n");
> + return false;
> + }
> }
>
> return true;
>
>
>
>
>
