S/390: Skip LT(G) peephole when literal pool is involved

S/390: Skip LT(G) peephole when literal pool is involved

By the time peephole optimizations run, we've already made up our mind
whether to use base-register or relative addressing for literal pool
entries.  LT(G) supports only base-register addressing, and so it is
too late to convert L(G)RL + compare to LT(G).  This change should not
make the code worse unless building with e.g. -fno-dce, since comparing
literal pool entries to zero should be optimized away during earlier
passes.

gcc/ChangeLog:

2018-11-20  Ilya Leoshkevich  <iii@linux.ibm.com>

	PR target/88083
	* config/s390/s390.md: Skip LT(G) peephole when literal pool is
	involved.
	* rtl.h (contains_constant_pool_address_p): New function.
	* rtlanal.c (contains_constant_pool_address_p): Likewise.

gcc/testsuite/ChangeLog:

2018-11-20  Ilya Leoshkevich  <iii@linux.ibm.com>

	PR target/88083
	* gcc.target/s390/pr88083.c: New test.

From-SVN: r266306