Re: Add utility functions for rtx broadcast/duplicate constants

[Jeff Law <law@redhat.com>]

On 08/20/2015 04:34 AM, Richard Sandiford wrote:
> Several pieces of code want to know whether all elements of a CONST_VECTOR
> are equal, and I'm about to add some more to simplify-rtx.c.  This patch
> adds some utility functions for that.
>
> I don't think we're really helping ourselves by having the shift
> amount in "v16qi << 3" be:
>
>      (const_vector:V16QI [
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>          (const_int 3)
>      ])
>
> so I wanted to leave open the possibility of using:
>
>      (const:V16QI (vec_duplicate:V16QI (const_int 3)))
>
> in future.  The interface therefore passes back the duplicated element
> rather than leaving callers to use CONST_VECTOR_ELT (c, 0)
> (== XVECEXP (c, 0, 0)).
>
> unwrap_const_vec_duplicate is mostly for code that handles vector
> operations equivalently to scalar ops.  The follow-on simplify-rtx.c
> code makes more use of this.  It also came in useful for the tilegx/
> tilepro predicates.
>
> Tested on x86_64-linux-gnu, arm-linux-gnueabi and aarch64-linux-gnu.
> I also built cross-compilers for s390x-linux-gnu, spu-elf, tilepro-elf
> and tilegx-elf and checked by hand that the affected code still worked.
> (Well, except for the SPU case.  That's handling vector constants in
> which the elements are symbolic addresses, such as
> { &foo, &foo, &foo, &foo }.  Such vectors don't seem to be treated as
> constants at the gimple level and the initial rtl code that we generate
> is too complex for later optimisations to convert back to a constant,
> so I wasn't sure how best to trigger it.)
>
> OK to install?
>
> Thanks,
> Richard
>
> gcc/
> 	* rtl.h (rtvec_all_equal_p): Declare.
> 	(const_vec_duplicate_p, unwrap_const_vec_duplicate): New functions.
> 	* rtl.c (rtvec_all_equal_p): New function.
> 	* expmed.c (expand_mult): Use unwrap_const_vec_duplicate.
> 	* config/aarch64/aarch64.c (aarch64_vect_float_const_representable_p)
> 	(aarch64_simd_dup_constant): Use const_vec_duplicate_p.
> 	* config/arm/arm.c (neon_vdup_constant): Likewise.
> 	* config/s390/s390.c (s390_contiguous_bitmask_vector_p): Likewise.
> 	* config/tilegx/constraints.md (W, Y): Likewise.
> 	* config/tilepro/constraints.md (W, Y): Likewise.
> 	* config/spu/spu.c (spu_legitimate_constant_p): Likewise.
> 	(classify_immediate): Use unwrap_const_vec_duplicate.
> 	* config/tilepro/predicates.md (reg_or_v4s8bit_operand): Likewise.
> 	(reg_or_v2s8bit_operand): Likewise.
> 	* config/tilegx/predicates.md (reg_or_v8s8bit_operand): Likewise.
> 	(reg_or_v4s8bit_operand): Likewise.
OK.
Jeff