Re: [PATCH 4/7] RISC-V: Recognize sign-extract + and cases for XVentanaCondOps

[Jeff Law <jeffreyalaw@gmail.com>]

On 11/12/22 14:29, Philipp Tomsich wrote:
> Users might use explicit arithmetic operations to create a mask and
> then and it, in a sequence like
>      cond = (bits >> SHIFT) & 1;
>      mask = ~(cond - 1);
>      val &= mask;
> which will present as a single-bit sign-extract.
>
> Dependening on what combination of XVentanaCondOps and Zbs are
> available, this will map to the following sequences:
>   - bexti + vt.maskc, if both Zbs and XVentanaCondOps are present
>   - andi + vt.maskc, if only XVentanaCondOps is available and the
>                      sign-extract is operating on bits 10:0 (bit
> 		    11 can't be reached, as the immediate is
> 		    sign-extended)
>   - slli + srli + and, otherwise.
>
> gcc/ChangeLog:
>
> 	* config/riscv/xventanacondops.md: Recognize SIGN_EXTRACT
> 	  of a single-bit followed by AND for XVentanaCondOps.
>
> Signed-off-by: Philipp Tomsich <philipp.tomsich@vrull.eu>
> ---
>
>   gcc/config/riscv/xventanacondops.md | 46 +++++++++++++++++++++++++++++
>   1 file changed, 46 insertions(+)
>
> diff --git a/gcc/config/riscv/xventanacondops.md b/gcc/config/riscv/xventanacondops.md
> index 7930ef1d837..3e9d5833a4b 100644
> --- a/gcc/config/riscv/xventanacondops.md
> +++ b/gcc/config/riscv/xventanacondops.md
> @@ -73,3 +73,49 @@
>     "TARGET_XVENTANACONDOPS"
>     [(set (match_dup 5) (match_dup 1))
>      (set (match_dup 0) (and:X (neg:X (ne:X (match_dup 5) (const_int 0)))
> +
> +;; Users might use explicit arithmetic operations to create a mask and
> +;; then and it, in a sequence like

Nit.  Seems like a word is missing.  "make and then and it"??


Do we really care about TARGET_XVENTANACONDOPS && ! TARGET_ZBS?


If there's a good reason to care about the !TARGET_ZBS case, then OK 
with the nit fixed.   If we agree that the !TARGET_ZBS case isn't all 
that important, then obviously OK with that pattern removed too.

I'm about out of oomph today.  I may take a look at 7/7 tonight though.  
Given it hits target independent code we probably want to get resolution 
on that patch sooner rather than later.

jeff