[gcc r13-3474] vect: Fix wrong shift_n after widening on BE [PR107338]

[gcc r13-3474] vect: Fix wrong shift_n after widening on BE [PR107338]

[Kewen Lin]

https://gcc.gnu.org/g:958014f369c8817184af110f8eb2c433a712fd0a

commit r13-3474-g958014f369c8817184af110f8eb2c433a712fd0a
Author: Kewen Lin <linkw@linux.ibm.com>
Date:   Tue Oct 25 00:18:08 2022 -0500

    vect: Fix wrong shift_n after widening on BE [PR107338]
    
    As PR107338 shows, with the use of widening loads, the
    container_type can become a wider type, it causes us to
    get wrong shift_n since the BIT_FIELD_REF offset actually
    becomes bigger on BE.  Taking the case in PR107338 as
    example, at the beginning the container type is short and
    BIT_FIELD_REF offset is 8 and size is 4, with unpacking to
    wider type int, the high 16 bits are zero, by viewing it
    as type int, its offset actually becomes to 24.  So the
    shift_n should be 4 (32 - 24 - 4) instead of 20 (32 - 8
    - 4).
    
    I noticed that if we move shift_n calculation early
    before the adjustments for widening loads (container type
    change), it's based on all the stuffs of the original
    container, the shfit_n calculated there is exactly what
    we want, it can be independent of widening.  Besides, I
    add prec adjustment together with the current adjustments
    for widening loads, although prec's subsequent uses don't
    require this change for now, since the container type gets
    changed, we should keep the corresponding prec consistent.
    
            PR tree-optimization/107338
    
    gcc/ChangeLog:
    
            * tree-vect-patterns.cc (vect_recog_bitfield_ref_pattern): Move
            shfit_n calculation before the adjustments for widening loads.

Diff:
---
 gcc/tree-vect-patterns.cc | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
index 777ba2f5903..4e2612e5b95 100644
--- a/gcc/tree-vect-patterns.cc
+++ b/gcc/tree-vect-patterns.cc
@@ -1925,6 +1925,16 @@ vect_recog_bitfield_ref_pattern (vec_info *vinfo, stmt_vec_info stmt_info,
   tree container_type = TREE_TYPE (container);
   tree vectype = get_vectype_for_scalar_type (vinfo, container_type);
 
+  /* Calculate shift_n before the adjustments for widening loads, otherwise
+     the container may change and we have to consider offset change for
+     widening loads on big endianness.  The shift_n calculated here can be
+     independent of widening.  */
+  unsigned HOST_WIDE_INT shift_n = bit_field_offset (bf_ref).to_constant ();
+  unsigned HOST_WIDE_INT mask_width = bit_field_size (bf_ref).to_constant ();
+  unsigned HOST_WIDE_INT prec = tree_to_uhwi (TYPE_SIZE (container_type));
+  if (BYTES_BIG_ENDIAN)
+    shift_n = prec - shift_n - mask_width;
+
   /* We move the conversion earlier if the loaded type is smaller than the
      return type to enable the use of widening loads.  */
   if (TYPE_PRECISION (TREE_TYPE (container)) < TYPE_PRECISION (ret_type)
@@ -1935,6 +1945,7 @@ vect_recog_bitfield_ref_pattern (vec_info *vinfo, stmt_vec_info stmt_info,
 			       NOP_EXPR, container);
       container = gimple_get_lhs (pattern_stmt);
       container_type = TREE_TYPE (container);
+      prec = tree_to_uhwi (TYPE_SIZE (container_type));
       vectype = get_vectype_for_scalar_type (vinfo, container_type);
       append_pattern_def_seq (vinfo, stmt_info, pattern_stmt, vectype);
     }
@@ -1953,12 +1964,6 @@ vect_recog_bitfield_ref_pattern (vec_info *vinfo, stmt_vec_info stmt_info,
 	shift_first = false;
     }
 
-  unsigned HOST_WIDE_INT shift_n = bit_field_offset (bf_ref).to_constant ();
-  unsigned HOST_WIDE_INT mask_width = bit_field_size (bf_ref).to_constant ();
-  unsigned HOST_WIDE_INT prec = tree_to_uhwi (TYPE_SIZE (container_type));
-  if (BYTES_BIG_ENDIAN)
-    shift_n = prec - shift_n - mask_width;
-
   /* If we don't have to shift we only generate the mask, so just fix the
      code-path to shift_first.  */
   if (shift_n == 0)