Re: [PATCH V4] VECT: Support LEN_MASK_{LOAD,STORE} ifn && optabs

[Robin Dapp <rdapp.gcc@gmail.com>]

Hi Juzhe,

> +@cindex @code{len_maskload@var{m}@var{n}} instruction pattern
> +@item @samp{len_maskload@var{m}@var{n}}
> +Perform a masked load (operand 2 - operand 4) elements from vector memory
> +operand 1 into vector register operand 0, setting the other elements of
> +operand 0 to undefined values.  This is a combination of len_load and maskload. 
> +Operands 0 and 1 have mode @var{m}, which must be a vector mode.  Operand 2
> +has whichever integer mode the target prefers.  A secondary mask is specified in
> +operand 3 which must be of type @var{n}.  Operand 4 conceptually has mode @code{QI}.
> +
> +Operand 2 can be a variable or a constant amount.  Operand 4 specifies a
> +constant bias: it is either a constant 0 or a constant -1.  The predicate on
> +operand 4 must only accept the bias values that the target actually supports.
> +GCC handles a bias of 0 more efficiently than a bias of -1.
> +
> +If (operand 2 - operand 4) exceeds the number of elements in mode
> +@var{m}, the behavior is undefined.
> +
> +If the target prefers the length to be measured in bytes
> +rather than elements, it should only implement this pattern for vectors
> +of @code{QI} elements.
> +
> +This pattern is not allowed to @code{FAIL}.

Please still change
"Perform a masked load (operand 2 - operand 4) elements"
to
"Perform a masked load of (operand 2 + operand 4) elements".

"vector memory operand" -> "memory operand"

As Richi has mentioned we are adding the negative bias not subtracting a positive
one.  You could also change the len_load and len_store comments while at it so
as to not introduce more confusion.

The "secondary" can also be omitted now because we don't have a primary mask
somewhere.  Maybe, for clarification, even if it's implicit:
"A mask is specified in operand 3 which must... The mask has lower precedence
than the length and is itself subject to length masking, i.e. only mask indices
<= (operand 2 + operand 4) are used."

> +
> +@cindex @code{len_maskstore@var{m}@var{n}} instruction pattern
> +@item @samp{len_maskstore@var{m}@var{n}}
> +Perform a masked store (operand 2 - operand 4) vector elements from vector register
> +operand 1 into memory operand 0, leaving the other elements of operand 0 unchanged.
> +This is a combination of len_store and maskstore.
> +Operands 0 and 1 have mode @var{m}, which must be a vector mode.  Operand 2 has whichever
> +integer mode the target prefers.  A secondary mask is specified in operand 3 which must be
> +of type @var{n}.  Operand 4 conceptually has mode @code{QI}.

Same thing applies here "store of (operand 2 + operand 4) vector elements as
well as the secondary.

Thanks.  No V5 necessary IMHO for those but let's see what Richard says.

Regards
 Robin