Mark constant-sized objects as addressable if they have poly-int accesses

If SVE code is written for a specific vector length, it might load from
or store to fixed-sized objects.  This needs to work even without
-msve-vector-bits=N (which should never be needed for correctness).

There's no way of handling a direct poly-int sized reference to a
fixed-size register; it would have to go via memory.  And in that
case it's more efficient to mark the fixed-size object as
addressable from the outset, like we do for array references
with non-constant indices.

2019-12-03  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* cfgexpand.c (discover_nonconstant_array_refs_r): If an access
	with POLY_INT_CST size is made to a fixed-size object, force the
	object to live in memory.

gcc/testsuite/
	* gcc.target/aarch64/sve/acle/general/deref_1.c: New test.

From-SVN: r278941

1 files changed, 15 insertions, 0 deletions

diff --git a/gcc/cfgexpand.c b/gcc/cfgexpand.c
index e8bed2504bf..bb31fef7014 100644
--- a/gcc/cfgexpand.c
+++ b/gcc/cfgexpand.c
@@ -6133,6 +6133,21 @@ discover_nonconstant_array_refs_r (tree * tp, int *walk_subtrees,
 
       *walk_subtrees = 0;
     }
+  /* References of size POLY_INT_CST to a fixed-size object must go
+     through memory.  It's more efficient to force that here than
+     to create temporary slots on the fly.  */
+  else if ((TREE_CODE (t) == MEM_REF || TREE_CODE (t) == TARGET_MEM_REF)
+	   && TYPE_SIZE (TREE_TYPE (t))
+	   && POLY_INT_CST_P (TYPE_SIZE (TREE_TYPE (t))))
+    {
+      tree base = get_base_address (t);
+      if (base
+	  && DECL_P (base)
+	  && DECL_MODE (base) != BLKmode
+	  && GET_MODE_SIZE (DECL_MODE (base)).is_constant ())
+	TREE_ADDRESSABLE (base) = 1;
+      *walk_subtrees = 0;
+    }
 
   return NULL_TREE;
 }