Ping!
Kindly review. The vmod instruction in powerpc are much more expensive
that using sequence of shifts/multiply/add.
Thanks and regards,
Avinash Jayakar
On Mon, 2025-09-15 at 17:09 +0530, Avinash Jayakar wrote:
> Hi,
>
> Below is a patch for fixing PR121700 proposed for master. Kindly
> review.
> Regtesting on powerpc64le is still running. Will update the status
> soon in this
> thread.
>
> Thank you,
> Avinash Jayakar
>
> rs6000: Update scalar cost of {TRUNC,FLOOR}_MOD_EXPR[PR121700]
>
> The default cost model with O2 flag is the VERY_CHEAP model which
> produces sub-optimal code for loops with TRUNC/FLOOR modulo
> expressions.
> Currently the vectorized variant of modulo operator is almost 4 times
> faster than scalar variant for 32 bit integeres on power10.
>
> In order to fairly compare scalar and vectorized variants of the loop
> in function vect_analyze_loop_costing, update the scalar cost for
> TRUNC_MOD_EXPR and FLOOR_MOD_EXPR. The value 6 is currently the
> number
> of instructions generated for these expressions with O2 flag.
>
> 2025-09-15 Avinash Jayakar <[email protected]>
>
> gcc/ChangeLog:
> PR target/121700
> * config/rs6000/rs6000.cc (rs6000_adjust_vect_cost_per_stmt):
> Add cost
> for {FLOOR,TRUNC}_MOD_EXPR.
> ---
> gcc/config/rs6000/rs6000.cc | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/gcc/config/rs6000/rs6000.cc
> b/gcc/config/rs6000/rs6000.cc
> index 8dd23f8619c..183e454c5bc 100644
> --- a/gcc/config/rs6000/rs6000.cc
> +++ b/gcc/config/rs6000/rs6000.cc
> @@ -5311,6 +5311,12 @@ rs6000_adjust_vect_cost_per_stmt (enum
> vect_cost_for_stmt kind,
> tree_code subcode = gimple_assign_rhs_code (stmt_info->stmt);
> if (subcode == COND_EXPR)
> return 2;
> +/* For {FLOOR,TRUNC}_MOD_EXPR, cost them a bit higher in order to
> fairly
> + compare the scalar and vector costs, since there is no direct
> instruction
> + that can evaluation these expressions with just 1 instruction.
> Currently
> + using the number of instructions generated for these
> expressions.*/
> + if (subcode == FLOOR_MOD_EXPR || subcode == TRUNC_MOD_EXPR)
> + return 6;
> }
>
> return 0;
