Re: [PATCH][ARM/AArch64] PR 68088: Fix RTL checking ICE due to subregs inside accumulator forwarding check

[Marcus Shawcroft <marcus.shawcroft@gmail.com>]

On 28 October 2015 at 10:07, Kyrill Tkachov <kyrylo.tkachov@arm.com> wrote:
> Hi all,
>
> This RTL checking error occurs on aarch64 in aarch_accumulator_forwarding
> when processing an msubsi insn
> with subregs:
> (insn 15 14 16 3 (set (reg/v:SI 78 [ i ])
>         (minus:SI (subreg:SI (reg/v:DI 76 [ aul ]) 0)
>             (mult:SI (subreg:SI (reg:DI 83) 0)
>                 (subreg:SI (reg:DI 75 [ _20 ]) 0)))) schedice.c:10 357
> {*msubsi}
>
> The register_operand predicate for that pattern allows subregs (I think
> correctly).
> The code in aarch_accumulator_forwarding doesn't take that into account and
> ends up
> taking a REGNO of a SUBREG, causing a checking error.
>
> This patch fixes that by stripping the subregs off the accumulator rtx
> before
> checking that the inner expression is a REG and taking its REGNO.
>
> The testcase now works fine with an aarch64-none-elf toolchain configure for
> RTL checking.
>
> The testcase is taken verbatim from the BZ entry for PR 68088.
> Since this function is shared between arm and aarch64 I've bootstrapped and
> tested it on both
> and I'll need ok's for both ports.
>
> Ok for trunk?

rtl.h exposes reg_or_subregno() already doesn't that do what we need here?

The test case is not aarch64 specific therefore I think convention is
that it should go into a generic directory.

Cheers
/Marcus