[AArch64] Make aarch64_classify_vector_mode use a switch statement

[James Greenhalgh]

On Wed, Aug 07, 2019 at 07:24:18PM +0100, Richard Sandiford wrote:
> aarch64_classify_vector_mode used properties of a mode to test whether
> the mode was a single Advanced SIMD vector, a single SVE vector, or a
> tuple of SVE vectors.  That works well for current trunk and is simpler
> than checking for modes by name.
> 
> However, for the ACLE and for planned autovec improvements, we also
> need partial SVE vector modes that hold:
> 
> - half of the available 32-bit elements
> - a half or quarter of the available 16-bit elements
> - a half, quarter, or eighth of the available 8-bit elements
> 
> These should be packed in memory and unpacked in registers.  E.g.
> VNx2SI has half the number of elements of VNx4SI, and so is half the
> size in memory.  When stored in registers, each VNx2SI element occupies
> the low 32 bits of a VNx2DI element, with the upper bits being undefined.
> 
> The upshot is that:
> 
>   GET_MODE_SIZE (VNx4SImode) == 2 * GET_MODE_SIZE (VNx2SImode)
> 
> since GET_MODE_SIZE must always be the memory size.  This in turn means
> that for fixed-length SVE, some partial modes can have the same size as
> Advanced SIMD modes.  We then need to be specific about which mode we're
> dealing with.
> 
> This patch prepares for that by switching based on the mode instead
> of querying properties.
> 
> A later patch makes sure that Advanced SIMD modes always win over
> partial SVE vector modes in normal queries.
> 
> Tested on aarch64-linux-gnu (with and without SVE) and aarch64_be-elf.
> OK to install?

OK.

Thanks,
James

> 
> Richard
> 
> 
> 2019-08-07  Richard Sandiford  <richard.sandiford@arm.com>
> 
> gcc/
> 	* config/aarch64/aarch64.c (aarch64_classify_vector_mode): Switch
> 	based on the mode instead of testing properties of it.