[055/nnn] poly_int: find_bswap_or_nop_load

[Richard Sandiford]

This patch handles polynomial offsets in find_bswap_or_nop_load,
which could be useful for constant-sized data at a variable offset.
It is needed for a later patch to compile.


2017-10-23  Richard Sandiford  <richard.sandif...@linaro.org>
            Alan Hayward  <alan.hayw...@arm.com>
            David Sherwood  <david.sherw...@arm.com>

gcc/
        * tree-ssa-math-opts.c (find_bswap_or_nop_load): Track polynomial
        offsets for MEM_REFs.

Index: gcc/tree-ssa-math-opts.c
===================================================================
--- gcc/tree-ssa-math-opts.c    2017-10-23 17:18:47.667056920 +0100
+++ gcc/tree-ssa-math-opts.c    2017-10-23 17:22:16.929564362 +0100
@@ -2122,35 +2122,31 @@ find_bswap_or_nop_load (gimple *stmt, tr
 
   if (TREE_CODE (base_addr) == MEM_REF)
     {
-      offset_int bit_offset = 0;
+      poly_offset_int bit_offset = 0;
       tree off = TREE_OPERAND (base_addr, 1);
 
       if (!integer_zerop (off))
        {
-         offset_int boff, coff = mem_ref_offset (base_addr);
-         boff = coff << LOG2_BITS_PER_UNIT;
+         poly_offset_int boff = mem_ref_offset (base_addr);
+         boff <<= LOG2_BITS_PER_UNIT;
          bit_offset += boff;
        }
 
       base_addr = TREE_OPERAND (base_addr, 0);
 
       /* Avoid returning a negative bitpos as this may wreak havoc later.  */
-      if (wi::neg_p (bit_offset))
+      if (may_lt (bit_offset, 0))
        {
-         offset_int mask = wi::mask <offset_int> (LOG2_BITS_PER_UNIT, false);
-         offset_int tem = wi::bit_and_not (bit_offset, mask);
-         /* TEM is the bitpos rounded to BITS_PER_UNIT towards -Inf.
-            Subtract it to BIT_OFFSET and add it (scaled) to OFFSET.  */
-         bit_offset -= tem;
-         tem >>= LOG2_BITS_PER_UNIT;
+         tree byte_offset = wide_int_to_tree
+           (sizetype, bits_to_bytes_round_down (bit_offset));
+         bit_offset = num_trailing_bits (bit_offset);
          if (offset)
-           offset = size_binop (PLUS_EXPR, offset,
-                                   wide_int_to_tree (sizetype, tem));
+           offset = size_binop (PLUS_EXPR, offset, byte_offset);
          else
-           offset = wide_int_to_tree (sizetype, tem);
+           offset = byte_offset;
        }
 
-      bitpos += bit_offset.to_shwi ();
+      bitpos += bit_offset.force_shwi ();
     }
 
   if (!multiple_p (bitpos, BITS_PER_UNIT, &bytepos))