This patch uses the workaround Richi suggested in the PR: make
discover_nonconstant_array_refs mark the source of an IFN_LOAD_LANES
call and the destination of an IFN_STORE_LANES call as addressable,
so that they don't end up being REG rtxes during expansion.

I had to move the discover_nonconstant_array_refs call outside the
currently_expanding_to_rtl block since otherwise mark_addressable
just queues the decision for later.

2019-09-05  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR middle-end/91577
	* cfgexpand.c (discover_nonconstant_array_refs): Force the source
	of an IFN_LOAD_LANES call and the destination of an IFN_STORE_LANES
	call to be in memory.
	(pass_expand::execute): Call discover_nonconstant_array_refs before
	setting currently_expanding_to_rtl.

gcc/testsuite/
	PR middle-end/91577
	* gfortran.dg/pr91577.f90: New test, taken from temporary_1.f90.

From-SVN: r275399