Add DR_BASE_ALIGNMENT and DR_BASE_MISALIGNMENT

Add DR_BASE_ALIGNMENT and DR_BASE_MISALIGNMENT

This patch records the base alignment and misalignment in
innermost_loop_behavior, to avoid the second-guessing that was
previously done in vect_compute_data_ref_alignment.  It also makes
vect_analyze_data_refs use dr_analyze_innermost, instead of having an
almost-copy of the same code.

I wasn't sure whether the alignments should be measured in bits
(for consistency with most other interfaces) or in bytes (for consistency
with DR_ALIGNED_TO, now DR_OFFSET_ALIGNMENT, and with *_ptr_info_alignment).
I went for bytes because:

- I think in practice most consumers are going to want bytes.
  E.g. using bytes avoids having to mix TYPE_ALIGN and TYPE_ALIGN_UNIT
  in vect_compute_data_ref_alignment.

- It means that any bit-level paranoia is dealt with when building
  the innermost_loop_behavior and doesn't get pushed down to consumers.

2017-07-03  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree-data-ref.h (innermost_loop_behavior): Add base_alignment
	and base_misalignment fields.
	(DR_BASE_ALIGNMENT, DR_BASE_MISALIGNMENT): New macros.
	* tree-data-ref.c: Include builtins.h.
	(dr_analyze_innermost): Set up the new innmost_loop_behavior fields.
	* tree-vectorizer.h (STMT_VINFO_DR_BASE_ALIGNMENT): New macro.
	(STMT_VINFO_DR_BASE_MISALIGNMENT): Likewise.
	* tree-vect-data-refs.c: Include tree-cfg.h.
	(vect_compute_data_ref_alignment): Use the new innermost_loop_behavior
	fields instead of calculating an alignment here.
	(vect_analyze_data_refs): Use dr_analyze_innermost.  Dump the new
	innermost_loop_behavior fields.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@249916 138bc75d-0d04-0410-961f-82ee72b054a4