https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120456
Bug ID: 120456
Summary: __builtin_shuffle produces unnecessary vperm2i128
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: adamant.pwn at gmail dot com
Target Milestone: ---
Consider the following snippet:
auto test1(uint32_t bits) {
auto bytes = u8x32(u32x8() + bits);
u8x32 shuffler = {
0, 0, 0, 0, 0, 0, 0, 0,
1, 1, 1, 1, 1, 1, 1, 1,
2, 2, 2, 2, 2, 2, 2, 2,
3, 3, 3, 3, 3, 3, 3, 3
};
auto shuffle = __builtin_shuffle(bytes, shuffler);
return shuffle;
}
It produces an unnecessary vperm2i128 command in the output. Same if I try to
use __builtin_shufflevector. Also if I try to change one of the bytes to the
second half, e.g. 3 to 31, it produces an unnecessary vpermq instead of
vperm2i128.
See https://godbolt.org/z/eEnd673e6 for details, and comparison with manual
implementation of the same function with intrinsics.
