Fix IFN_MASK_STORE handling of IFN_GOMP_SIMD_LANE

The IFN_GOMP_SIMD_LANE handling in vectorizable_store tries to use MEM_REF
offsets to maintain pointer disambiguation info.  This patch makes sure
that we don't try to do the same optimisation for IFN_MASK_STOREs, which
have no similar offset argument.

The patch fixes libgomp.c-c++-common/pr66199-*.c for SVE.  Previously
we had an ncopies==2 store and stored both halves to the same address.

2019-01-07  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-stmts.c (vectorizable_store): Don't use the dataref_offset
	optimization for masked stores.

From-SVN: r267654

gcc/ChangeLog

 2019-01-07  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* tree-vect-stmts.c (vectorizable_store): Don't use the dataref_offset
+	optimization for masked stores.
+
+2019-01-07  Richard Sandiford  <richard.sandiford@arm.com>
+
 	PR middle-end/88567
 	* tree-vect-loop.c (get_initial_defs_for_reduction): Pass the
 	output vector directly to duplicate_and_interleave instead of

gcc/tree-vect-stmts.c

@@ -7059,6 +7059,7 @@ vectorizable_store (stmt_vec_info stmt_info, gimple_stmt_iterator *gsi,
 	  bool simd_lane_access_p
 	    = STMT_VINFO_SIMD_LANE_ACCESS_P (stmt_info);
 	  if (simd_lane_access_p
+	      && !loop_masks
 	      && TREE_CODE (DR_BASE_ADDRESS (first_dr_info->dr)) == ADDR_EXPR
 	      && VAR_P (TREE_OPERAND (DR_BASE_ADDRESS (first_dr_info->dr), 0))
 	      && integer_zerop (DR_OFFSET (first_dr_info->dr))