[PATCH] D56311: [SelectionDAG][RFC] Allow the user to specify a memeq function (v2).
Clement Courbet via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri Jan 4 02:24:42 PST 2019
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 using a module flag, e.g.:
!llvm.module.flags = !{..., !123}
!123 = !{i32 1, !"memeq_lib_function", !"user_memeq"}
This function 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/D56311
Files:
lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
test/CodeGen/X86/memcmp-memeq.ll
test/CodeGen/X86/memcmp.ll
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D56311.180208.patch
Type: text/x-patch
Size: 12562 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190104/94b1eef9/attachment.bin>
More information about the llvm-commits
mailing list