[IRA] some code improvement and s390 support

Ulrich Weigand uweigand@de.ibm.com
Mon Sep 1 16:51:00 GMT 2014


Vladmir Makarov wrote:

> 	* config/s390/s390.h (IRA_COVER_CLASSES,
> 	IRA_HARD_REGNO_ADD_COST_MULTIPLIER(regno)): Define.

In debugging PR 53854 I noticed a strange behavior in IRA costs
that seems to trace back to the very first definition of the
IRA_HARD_REGNO_ADD_COST_MULTIPLIER on s390:

> +/* In some case register allocation order is not enough for IRA to
> +   generate a good code.  The following macro (if defined) increases
> +   cost of REGNO for a pseudo approximately by pseudo usage frequency
> +   multiplied by the macro value.
> +
> +   We avoid usage of BASE_REGNUM by nonzero macro value because the
> +   reload can decide not to use the hard register because some
> +   constant was forced to be in memory.  */
> +#define IRA_HARD_REGNO_ADD_COST_MULTIPLIER(regno)	\
> +  (regno == BASE_REGNUM ? 0.0 : 0.5)

(which is still unchanged in current sources.)

Now, the comment says BASE_REGNUM should be avoided, but the actual
implementation of the macro seems to avoid *all* registers *but*
BASE_REGNUM ...

Am I misreading this, or is there indeed a logic error here?

Bye,
Ulrich

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



More information about the Gcc-patches mailing list