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


Robin Dapp wrote:

>         * config/s390/s390.c (preferred_la_operand_p): Do not use
> 	LA with base and index on z13 or later.

The code just before your change reads:

  /* 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)
    return false;

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.)

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU/Linux compilers and toolchain
  Ulrich.Weigand@de.ibm.com


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