[PATCH] D56248: [SelectionDAG][RFC] Allow the user to specify a memeq function.

[Clement Courbet via Phabricator via llvm-commits]

courbet created this revision.

Right now, when we encounter a string equality check,
e.g. `if (memcmp(a, b, s) == 0)`, we try to expand to a comparison if `s` is a
small compile-time constant, and fall back on calling `memcmp()` else.

This is sub-optimal because memcmp has to compute much more than
equality.

This patch adds a way for the user to specify a `memeq` library
function (e.g. `-memeq-lib-function=user_memeq`) which will be called
instead of `memcmp()` when the result of the memcmp call is only used
for equality comparison.

`memeq` can be made much more efficient than `memcmp` because equality
compare is trivially parallel while lexicographic ordering has a chain
dependency.


Repository:
  rL LLVM

https://reviews.llvm.org/D56248

Files:
  lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
  test/CodeGen/X86/memcmp.ll

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D56248.180005.patch
Type: text/x-patch
Size: 17962 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190103/ef07ac9b/attachment-0001.bin>