[Bug target/78683] [ppc] __builtin_ctzl code gen can be improved for -mcpu=power8 and earlier

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78683

--- Comment #1 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Author: segher
Date: Fri Dec  9 19:31:06 2016
New Revision: 243499

URL: https://gcc.gnu.org/viewcvs?rev=243499&root=gcc&view=rev
Log:
rs6000: clz/ctz/ffs improvement (PR78683)

On CPUs that implement popcnt[wd] but not cnttz[wd] we can do better for
the ctz sequences than we do today.

CL[TZ]_DEFINED_VALUE_AT_ZERO can return 2, since we always return the
same fixed value (only dependent on TARGET_* options).


        PR target/78683
        * config/rs6000/rs6000.h (CLZ_DEFINED_VALUE_AT_ZERO): Use
        GET_MODE_BITSIZE.  Return 2.
        (CTZ_DEFINED_VALUE_AT_ZERO): Use GET_MODE_BITSIZE.  Return 2.  Handle
        TARGET_POPCNTD the same as TARGET_CTZ.
        * config/rs6000/rs6000.md (ctz<mode>2): Reimplement.
        (ffs<mode>2): Reimplement.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/rs6000/rs6000.h
    trunk/gcc/config/rs6000/rs6000.md