[036/nnn] poly_int: get_object_alignment_2

[Richard Sandiford]

This patch makes get_object_alignment_2 track polynomial offsets
and sizes.  The real work is done by get_inner_reference, but we
then need to handle the alignment correctly.


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

gcc/
        * builtins.c (get_object_alignment_2): Track polynomial offsets
        and sizes.  Update the alignment handling.

Index: gcc/builtins.c
===================================================================
--- gcc/builtins.c      2017-10-23 17:11:39.984447382 +0100
+++ gcc/builtins.c      2017-10-23 17:18:42.394520412 +0100
@@ -252,7 +252,7 @@ called_as_built_in (tree node)
 get_object_alignment_2 (tree exp, unsigned int *alignp,
                        unsigned HOST_WIDE_INT *bitposp, bool addr_p)
 {
-  HOST_WIDE_INT bitsize, bitpos;
+  poly_int64 bitsize, bitpos;
   tree offset;
   machine_mode mode;
   int unsignedp, reversep, volatilep;
@@ -377,8 +377,17 @@ get_object_alignment_2 (tree exp, unsign
        }
     }
 
+  /* Account for the alignment of runtime coefficients, so that the constant
+     bitpos is guaranteed to be accurate.  */
+  unsigned int alt_align = ::known_alignment (bitpos - bitpos.coeffs[0]);
+  if (alt_align != 0 && alt_align < align)
+    {
+      align = alt_align;
+      known_alignment = false;
+    }
+
   *alignp = align;
-  *bitposp = bitpos & (*alignp - 1);
+  *bitposp = bitpos.coeffs[0] & (align - 1);
   return known_alignment;
 }