Re: [x86 PATCH] PR target/113231: Improved costs in Scalar-To-Vector (STV) pass.

[Uros Bizjak <ubizjak@gmail.com>]

On Sat, Jan 6, 2024 at 2:30 PM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> This patch improves the cost/gain calculation used during the i386 backend's
> SImode/DImode scalar-to-vector (STV) conversion pass.  The current code
> handles loads and stores, but doesn't consider that converting other
> scalar operations with a memory destination, requires an explicit load
> before and an explicit store after the vector equivalent.
>
> To ease the review, the significant change looks like:
>
>          /* For operations on memory operands, include the overhead
>             of explicit load and store instructions.  */
>          if (MEM_P (dst))
>            igain += !optimize_insn_for_size_p ()
>                     ? (m * (ix86_cost->int_load[2]
>                             + ix86_cost->int_store[2])
>                        - (ix86_cost->sse_load[sse_cost_idx] +
>                           ix86_cost->sse_store[sse_cost_idx]))
>                     : -COSTS_N_BYTES (8);

Please just swap true and false statements to avoid negative test.

> however the patch itself is complicated by a change in indentation
> which leads to a number of lines with only whitespace changes.

'git diff -w' to the rescue ;)

> For architectures where integer load/store costs are the same as
> vector load/store costs, there should be no change without -Os/-Oz.
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}
> with no new failures.  Ok for mainline?
>
>
> 2024-01-06  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         PR target/113231
>         * config/i386/i386-features.cc (compute_convert_gain): Include
>         the overhead of explicit load and store (movd) instructions when
>         converting non-store scalar operations with memory destinations.
>
> gcc/testsuite/ChangeLog
>         PR target/113231
>         * gcc.target/i386/pr113231.c: New test case.

OK with the above proposed change.

Thanks,
Uros.