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Re: Variations of memset()

On Fri, 4 Aug 2017, Matthew Wilcox wrote:

> void *memset16(uint16_t *s, uint16_t v, size_t count);
> void *memset32(uint32_t *s, uint32_t v, size_t count);
> void *memset64(uint64_t *s, uint64_t v, size_t count);

Is your assertion that there are useful optimizations for these that 
result in code too large for it to make sense for the compiler to inline 
it, so an out-of-line function call is appropriate instead?  I'd expect 
the compiler to vectorize memset-like loops where appropriate, inline, 
without needing such functions.  Or is the desire to use IFUNCs for such 
functions so code can be optimized for the processor it is running on, 
without needing to be compiled for each processor with different vector 
instructions that should be used?

(As noted, wmemset already provides memset32 semantics for all glibc 
configurations, subject to any ABI questions of sign/zero extension of the 
second argument for some ABIs if wchar_t is signed and this affects how 
the argument is passed compared to uint32_t.)

Joseph S. Myers

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