Messages in this thread | | | Date | Mon, 4 May 2015 17:10:55 -0500 | From | Segher Boessenkool <> | Subject | Re: [v2,2/2] powerpc32: add support for csum_add() |
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On Fri, May 01, 2015 at 08:00:14PM -0500, Scott Wood wrote: > On Tue, 2015-04-28 at 21:01 +0200, christophe leroy wrote: > > The generated code is most likely different on ppc64. I have no ppc64 > > compiler
For reference: yes you do. Just add -m64.
> Ideal (short of a 64-bit __wsum) would probably be something like (untested): > > add r3,r3,r4 > srdi r5,r3,32 > add r3,r3,r5 > clrldi r3,r3,32 > > Or in C code (which would let the compiler schedule it better): > > static inline __wsum csum_add(__wsum csum, __wsum addend) > { > u64 res = (__force u64)csum; > res += (__force u32)addend; > return (__force __wsum)((u32)res + (res >> 32)); > }
Older GCC make exactly your asm code for that, in 64-bit; newer GCC get two adds (one as 32-bit, one as 64-bit, it does not see those are the same, grrr); and GCC 5 makes the perfect addc 3,4,3 ; addze 3,3 for this in 32-bit mode. You don't want to see what older GCC does with 32-bit though :-/
Segher
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