poly_int: get_object_alignment_2

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.

2017-12-20  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

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

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r255893

gcc/ChangeLog

@@ -2,6 +2,13 @@
 	    Alan Hayward  <alan.hayward@arm.com>
 	    David Sherwood  <david.sherwood@arm.com>
 
+	* builtins.c (get_object_alignment_2): Track polynomial offsets
+	and sizes.  Update the alignment handling.
+
+2017-12-20  Richard Sandiford  <richard.sandiford@linaro.org>
+	    Alan Hayward  <alan.hayward@arm.com>
+	    David Sherwood  <david.sherwood@arm.com>
+
 	* tree.h (get_inner_reference): Add a version that returns the
 	offset and size as poly_int64_pods rather than HOST_WIDE_INTs.
 	* cfgexpand.c (expand_debug_expr): Track polynomial offsets.  Simply

gcc/builtins.c

@@ -248,7 +248,7 @@ static bool
 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;
@@ -373,8 +373,17 @@ get_object_alignment_2 (tree exp, unsigned int *alignp,
 	}
     }
 
+  /* 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;
 }