[PATCH] D137361: IR: Add atomicrmw uinc_wrap and udec_wrap

[Ruiling, Song via Phabricator via llvm-commits]

ruiling added inline comments.


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Comment at: llvm/docs/LangRef.rst:10471
+-  udec_wrap: ``*ptr = ((*ptr == 0) || (*ptr u> val)) ? val : (*ptr - 1)``
 
 Example:
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JonChesterfield wrote:
> The expressions here look suspicious - I thought these operated as inc/dec then modulo value. Does inc(p,10) really go to zero if p has the initial value 15? If so clamp might be a better name.
> 
> Likewise the ==0 in dec, though I think unsigned compare makes that expression work. Is it *ptr = ((*ptr -1) % val) ?
> 
> 
The two operations work like maintaining the pointer to a circular/ring buffer (with `val+1` elements). The uinc_wrap would move the pointer forward while the udec_wrap would move the pointer backward. IMO, this is more of a wrap-around than clamp.


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  https://reviews.llvm.org/D137361/new/

https://reviews.llvm.org/D137361