[PATCH] D97667: [loop-idiom] Hoist loop memcpys to loop preheader

[Theodore Popp via Phabricator via llvm-commits]

tpopp added a comment.

Describing what the code is intended to do (https://github.com/tensorflow/tensorflow/blob/master/tensorflow/compiler/xla/tests/reverse_test.cc#L146).

A 4d array is taking in reversing elements across the 0th and 1st dimensions, so for every value previously indexed at [A,B,C,D] in an array of size [W,X,Y,Z], the new index of the value is [W-A-1, X-B-1, C, D].

The original code indexes into proper locations for the first 2 dimensions, and then copies the subdata, while this change results in a single copy after indexing only in dimension 0, which cannot be done as the data in dimension 1 cannot be copied due to the reversal.


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  https://reviews.llvm.org/D97667/new/

https://reviews.llvm.org/D97667