[PATCH, S390] Avoid LA with base and index on z13

[Robin Dapp <rdapp at linux dot ibm dot com>]

> But on zEC12 LA works pretty much the same as on z13/z14, it is
> indeed not cracked, but still a 2-cycle instruction when using
> an index register.  So I guess the change really should apply
> to zEC12 as well, and this could be as simple as changing the
> above line to:
> 
>   if (addr.indx && s390_tune >= PROCESSOR_2817_Z196)
> 
> (Note that "addr.base && addr.indx" is the same as just checking
> for addr.indx, since s390_decompose_address will never fill in
> *just* an index.)

Good point, I adapted the patch and changed the comment.

Regards
 Robin

--

gcc/ChangeLog:

2018-07-16  Robin Dapp  <rdapp@linux.ibm.com>

	* config/s390/s390.c (preferred_la_operand_p): Do not use
	LA with index register on z196 or later.

diff --git a/gcc/config/s390/s390.c b/gcc/config/s390/s390.c
index 23c3f3db621..d8b47c6fe67 100644
--- a/gcc/config/s390/s390.c
+++ b/gcc/config/s390/s390.c
@@ -4623,11 +4623,11 @@ preferred_la_operand_p (rtx op1, rtx op2)
   if (addr.indx && !REGNO_OK_FOR_INDEX_P (REGNO (addr.indx)))
     return false;
 
-  /* Avoid LA instructions with index register on z196; it is
-     preferable to use regular add instructions when possible.
-     Starting with zEC12 the la with index register is "uncracked"
-     again.  */
-  if (addr.indx && s390_tune == PROCESSOR_2817_Z196)
+  /* Avoid LA instructions with index (and base) register on z196 or
+     later; it is preferable to use regular add instructions when
+     possible.  Starting with zEC12 the la with index register is
+     "uncracked" again but still slower than a regular add.  */
+  if (addr.indx && s390_tune >= PROCESSOR_2817_Z196)
     return false;
 
   if (!TARGET_64BIT && !addr.pointer)