[LLVMdev] Memset/memcpy: user control of loop-idiom recognizer

[Robert Lougher]

On 2 December 2014 at 19:57, Joerg Sonnenberger <joerg at britannica.bec.de> wrote:
> On Tue, Dec 02, 2014 at 07:23:01PM +0000, Robert Lougher wrote:
>> In feedback from game studios a common issue is the replacement of
>> loops with calls to memcpy/memset.  These loops are often
>> hand-optimised, and highly-efficient and the developers strongly want
>> a way to control the compiler (i.e. leave my loop alone).
>
> I doubt that. If anything, it means the lowering of the intrinsic is
> bad, not that the transformation should not happen.
>
> Joerg

Yes, that's why I talked about variable and constant trip-counts.  For
constant loops there generally isn't a problem, as they can be lowered
inline (if small).  Variable loops, however, get expanded into a
library call.

Rob.

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