Re: Be stricter about CONST_VECTOR operands

[James Greenhalgh <james dot greenhalgh at arm dot com>]

On Mon, Nov 06, 2017 at 09:10:23AM +0000, Richard Sandiford wrote:
> The recent gen_vec_duplicate patches used CONST_VECTOR for all
> constants, but the documentation says:
> 
>   @findex const_vector
>   @item (const_vector:@var{m} [@var{x0} @var{x1} @dots{}])
>   Represents a vector constant.  The square brackets stand for the vector
>   containing the constant elements.  @var{x0}, @var{x1} and so on are
>   the @code{const_int}, @code{const_double} or @code{const_fixed} elements.
> 
> Both the AArch32 and AArch64 ports relied on the elements having
> this form and would ICE if the element was something like a CONST
> instead.  This showed up as a failure in vect-102.c for both arm-eabi
> and aarch64-elf (but not aarch64-linux-gnu, which is what the series
> was tested on).
> 
> The two obvious options were to redefine CONST_VECTOR to accept all
> constants or make gen_vec_duplicate honour the existing documentation.
> It looks like other code also assumes that integer CONST_VECTORs contain
> CONST_INTs, so the patch does the latter.
> 
> I deliberately didn't add an assert to gen_const_vec_duplicate
> because it looks like the SPU port *does* expect to be able to create
> CONST_VECTORs of symbolic constants.
> 
> Also, I think the list above should include const_wide_int for vectors
> of TImode and wider.
> 
> The new routine takes a mode for consistency with the generators,
> and because I think it does make sense to accept all constants for
> variable-length:
> 
>     (const (vec_duplicate ...))
> 
> rather than have some rtxes for which we instead use:
> 
>     (vec_duplicate (const ...))
> 
> Tested on aarch64-elf, aarch64-linux-gnu, x86_64-linux-gnu and
> powerpc64-linux-gnu.  OK to install?

For what it is worth, I can see why this would fix the bug in the AArch64
port, and the patch looks good to me (though I can't approve it).

> (but not aarch64-linux-gnu, which is what the series was tested on).

Presumably it would fail there for -mcmodel=tiny too, we just don't run
that variant by default.

Thanks,
James

> 2017-11-06  Richard Sandiford  <richard.sandiford@linaro.org>
> 
> gcc/
> 	* doc/rtl.texi (const_vector): Say that elements can be
> 	const_wide_ints too.
> 	* emit-rtl.h (valid_for_const_vec_duplicate_p): Declare.
> 	* emit-rtl.c (valid_for_const_vec_duplicate_p): New function.
> 	(gen_vec_duplicate): Use it instead of CONSTANT_P.
> 	* optabs.c (expand_vector_broadcast): Likewise.