S/390: Make "b" constraint match literal pool references

Improves the code generation by getting rid of redundant LAs, as seen
in the following example:

	-	la	%r1,0(%r13)
	-	lg	%r4,0(%r1)
	+	lg	%r4,0(%r13)

Also allows to proceed with the merge of movdi_64 and movdi_larl.
Currently LRA decides to spill literal pool references back to the
literal pool, because it preliminarily chooses alternatives with
CT_MEMORY constraints without calling
satisfies_memory_constraint_p (). Later on it notices that the
constraint is wrong and fixes it by spilling.  The constraint in this
case is "b", and the operand is a literal pool reference.  There is
no reason to reject them.  The current behavior was introduced,
apparently unintentionally, by
https://gcc.gnu.org/ml/gcc-patches/2010-09/msg00812.html

The patch affects a little bit more than mentioned in the subject,
because it changes s390_loadrelative_operand_p (), which is called not
only for checking the "b" constraint.  However, the only caller for
which it should really not accept literal pool references is
s390_check_qrst_address (), so it was changed to explicitly do so.

gcc/ChangeLog:

2018-10-22  Ilya Leoshkevich  <iii@linux.ibm.com>

	* config/s390/s390.c (s390_loadrelative_operand_p): Accept
	literal pool references.
	(s390_check_qrst_address): Adapt to the new behavior of
	s390_loadrelative_operand_p ().

gcc/testsuite/ChangeLog:

2018-10-22  Ilya Leoshkevich  <iii@linux.ibm.com>

	* gcc.target/s390/litpool-int.c: New test.

From-SVN: r265371

gcc/ChangeLog

+2018-10-22  Ilya Leoshkevich  <iii@linux.ibm.com>
+
+	* config/s390/s390.c (s390_loadrelative_operand_p): Accept
+	literal pool references.
+	(s390_check_qrst_address): Adapt to the new behavior of
+	s390_loadrelative_operand_p ().
+
 2018-10-22  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/72782

gcc/config/s390/s390.c

@@ -3110,8 +3110,7 @@ s390_legitimate_address_without_index_p (rtx op)
    Valid addresses are single references or a sum of a reference and a
    constant integer. Return these parts in SYMREF and ADDEND.  You can
    pass NULL in REF and/or ADDEND if you are not interested in these
-   values.  Literal pool references are *not* considered symbol
-   references.  */
+   values.  */
 
 static bool
 s390_loadrelative_operand_p (rtx addr, rtx *symref, HOST_WIDE_INT *addend)
@@ -3130,7 +3129,7 @@ s390_loadrelative_operand_p (rtx addr, rtx *symref, HOST_WIDE_INT *addend)
       addr = XEXP (addr, 0);
     }
 
-  if ((GET_CODE (addr) == SYMBOL_REF && !CONSTANT_POOL_ADDRESS_P (addr))
+  if (GET_CODE (addr) == SYMBOL_REF
       || (GET_CODE (addr) == UNSPEC
 	  && (XINT (addr, 1) == UNSPEC_GOTENT
 	      || XINT (addr, 1) == UNSPEC_PLT)))
@@ -3153,6 +3152,7 @@ s390_loadrelative_operand_p (rtx addr, rtx *symref, HOST_WIDE_INT *addend)
 static int
 s390_check_qrst_address (char c, rtx op, bool lit_pool_ok)
 {
+  rtx symref;
   struct s390_address addr;
   bool decomposed = false;
 
@@ -3161,7 +3161,8 @@ s390_check_qrst_address (char c, rtx op, bool lit_pool_ok)
 
   /* This check makes sure that no symbolic address (except literal
      pool references) are accepted by the R or T constraints.  */
-  if (s390_loadrelative_operand_p (op, NULL, NULL))
+  if (s390_loadrelative_operand_p (op, &symref, NULL)
+      && (!lit_pool_ok || !CONSTANT_POOL_ADDRESS_P (symref)))
     return 0;
 
   /* Ensure literal pool references are only accepted if LIT_POOL_OK.  */

gcc/testsuite/ChangeLog

+2018-10-22  Ilya Leoshkevich  <iii@linux.ibm.com>
+
+	* gcc.target/s390/litpool-int.c: New test.
+
 2018-10-22  H.J. Lu  <hongjiu.lu@intel.com>
 
 	PR target/72782