[Bug target/93177] PPC: Missing many useful platform intrinsics

[segher at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93177

--- Comment #7 from Segher Boessenkool <segher at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #5)
> >the cntlz ones are not, for example
> 
> :)  It has been a long time since I touched this but I would not doubt I
> messed up this too.

It's nastiness in the generic builtins.  builtin_clz(0) is undefined, even
if it *is* defined for the machine pattern.  This is so that code using the
builtin can be portable.  Unfortunately there is no good way (or I don't know
it, anyway) to do something like

  int f(int x) { return x ? __builtin_clz(x) : 32; }

so that it compiles to just a cntlzw insn (instead, it currently does a branch
and stuff :-( ).

> __mulh* intrinsics are better implemented these days using either 64bit or
> 128bit multiples.

Yup.

> __l[hwd]brx/__st[hwd]brx intrinsics are better implemented as
> __builtin_bswap* followed by load/stored these days (the bswap builtins did
> not exist back then or optimized)

Yup.

> Many of the other intrinsics should be implemented as non inline-asm too,
> even fma, should be done using __builtin_fma :).

Yup :-)

GCC has come a long way, since Cell :-)  You can reliably write many things
just as high-level C code now, and trust that well-optimised machine code
falls out.