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.

From-SVN: r249916

1 files changed, 38 insertions, 0 deletions

diff --git a/gcc/tree-data-ref.h b/gcc/tree-data-ref.h
index 3a5068d..72c68d0 100644
--- a/gcc/tree-data-ref.h
+++ b/gcc/tree-data-ref.h
@@ -52,6 +52,42 @@ struct innermost_loop_behavior
   tree init;
   tree step;
 
+  /* BASE_ADDRESS is known to be misaligned by BASE_MISALIGNMENT bytes
+     from an alignment boundary of BASE_ALIGNMENT bytes.  For example,
+     if we had:
+
+       struct S __attribute__((aligned(16))) { ... };
+
+       char *ptr;
+       ... *(struct S *) (ptr - 4) ...;
+
+     the information would be:
+
+       base_address:      ptr
+       base_aligment:      16
+       base_misalignment:   4
+       init:               -4
+
+     where init cancels the base misalignment.  If instead we had a
+     reference to a particular field:
+
+       struct S __attribute__((aligned(16))) { ... int f; ... };
+
+       char *ptr;
+       ... ((struct S *) (ptr - 4))->f ...;
+
+     the information would be:
+
+       base_address:      ptr
+       base_aligment:      16
+       base_misalignment:   4
+       init:               -4 + offsetof (S, f)
+
+     where base_address + init might also be misaligned, and by a different
+     amount from base_address.  */
+  unsigned int base_alignment;
+  unsigned int base_misalignment;
+
   /* The largest power of two that divides OFFSET, capped to a suitably
      high value if the offset is zero.  This is a byte rather than a bit
      quantity.  */
@@ -147,6 +183,8 @@ struct data_reference
 #define DR_INIT(DR)                (DR)->innermost.init
 #define DR_STEP(DR)                (DR)->innermost.step
 #define DR_PTR_INFO(DR)            (DR)->alias.ptr_info
+#define DR_BASE_ALIGNMENT(DR)      (DR)->innermost.base_alignment
+#define DR_BASE_MISALIGNMENT(DR)   (DR)->innermost.base_misalignment
 #define DR_OFFSET_ALIGNMENT(DR)    (DR)->innermost.offset_alignment
 #define DR_STEP_ALIGNMENT(DR)      (DR)->innermost.step_alignment
 #define DR_INNERMOST(DR)           (DR)->innermost