diff --git a/gcc/tree-ssa-sccvn.cc b/gcc/tree-ssa-sccvn.cc
index b9f289b6eca..fa2f65df159 100644
--- a/gcc/tree-ssa-sccvn.cc
+++ b/gcc/tree-ssa-sccvn.cc
@@ -2090,7 +2090,7 @@ vn_walk_cb_data::push_partial_def (pd_data pd,
 	    len = ROUND_UP (pd.size, BITS_PER_UNIT) / BITS_PER_UNIT;
 	  memset (this_buffer, 0, len);
 	}
-      else
+      else if (pd.rhs_off >= 0)
 	{
 	  len = native_encode_expr (pd.rhs, this_buffer, bufsize,
 				    (MAX (0, -pd.offset)
@@ -2105,6 +2105,24 @@ vn_walk_cb_data::push_partial_def (pd_data pd,
 	      return (void *)-1;
 	    }
 	}
+      else /* negative pd.rhs_off indicates we want to chop off first bits */
+	{
+	  if (-pd.rhs_off >= bufsize)
+	    return (void *)-1;
+	  len = native_encode_expr (pd.rhs,
+				    this_buffer + -pd.rhs_off / BITS_PER_UNIT,
+				    bufsize - -pd.rhs_off / BITS_PER_UNIT,
+				    MAX (0, -pd.offset) / BITS_PER_UNIT);
+	  if (len <= 0
+	      || len < (ROUND_UP (pd.size, BITS_PER_UNIT) / BITS_PER_UNIT
+			- MAX (0, -pd.offset) / BITS_PER_UNIT))
+	    {
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		fprintf (dump_file, "Failed to encode %u "
+			 "partial definitions\n", ndefs);
+	      return (void *)-1;
+	    }
+	}
 
       unsigned char *p = buffer;
       HOST_WIDE_INT size = pd.size;
@@ -3349,10 +3367,13 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *data_,
 		}
 	      else if (fn == IFN_LEN_STORE)
 		{
-		  pd.rhs_off = 0;
 		  pd.offset = offset2i;
 		  pd.size = (tree_to_uhwi (len)
 			     + -tree_to_shwi (bias)) * BITS_PER_UNIT;
+		  if (BYTES_BIG_ENDIAN)
+		    pd.rhs_off = pd.size - tree_to_uhwi (TYPE_SIZE (vectype));
+		  else
+		    pd.rhs_off = 0;
 		  if (ranges_known_overlap_p (offset, maxsize,
 					      pd.offset, pd.size))
 		    return data->push_partial_def (pd, set, set,