[3/n] PR85694: Fix dummy assignment handling in vectorizable_call

[3/n] PR85694: Fix dummy assignment handling in vectorizable_call

vectorizable_call stubs out the original scalar statement with
a dummy assignment to the same lhs, so that we don't leave any bogus
scalar calls around.  If the call is actually a pattern statement,
the code rightly took the lhs of the original bb statement:

  if (is_pattern_stmt_p (stmt_info))
    lhs = gimple_call_lhs (STMT_VINFO_RELATED_STMT (stmt_info));
  else
    lhs = gimple_call_lhs (stmt);

But it then associated the new statement with the stmt_vec_info of the
pattern statement rather than the bb statement, which meant we had two
stmt_vec_infos assigning to the same lhs.  This seems to be latent at
the moment but caused problems further into the series.

2018-06-20  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vect-stmts.c (vectorizable_call): Make sure that we
	use the stmt_vec_info of the original bb statement for the
	new zero assignment, even if the call is part of a pattern.

From-SVN: r261786