On Mon, May 30, 2022 at 3:22 PM Roger Sayle <ro...@nextmovesoftware.com> wrote:
>
>
> This patch is a form of insurance policy in case my patch for PR 7061 runs
> into problems on non-x86 targets; the middle-end can add an extra check
> that the backend is happy placing SCmode and DImode values in the same
> register, before creating a SUBREG. Unfortunately, ix86_modes_tieable_p
> currently claims this is not allowed(?), even though the default target
> hook for modes_tieable_p is to always return true [i.e. false can be
> used to specifically prohibit bad combinations], and the x86_64 ABI
> passes SCmode values in DImode registers!. This makes the backend's
> modes_tiable_p hook a little more forgiving, and additionally enables
> interconversion between SCmode and V2SFmode, and between DCmode and
> VD2Fmode, which opens interesting opportunities in the future.
>
> I believe there should currently be no code generation differences
> with this change. 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?
>
>
> 2022-05-30 Roger Sayle <ro...@nextmovesoftware.com>
>
> gcc/ChangeLog
> * config/i386/i386.cc (ix86_modes_tieable_p): Allow SCmode to be
> tieable with DImode on TARGET_64BIT, and SCmode tieable with
> V2SFmode, and DCmode with V2DFmode.
I *think* this is OK, but hard to say for sure without some testcases.
Please note that x86_64 ABI passes SDmode in two separate XMM
registers.
Uros.
