There could be some mis-alignments when copying origins not aligned.
I believe inaligned memcpy is rare so the cases do not matter too much
in practice.
1) About the change at line 50
Let dst be (void*)5,
then d=5, beg=4
so we need to write 3 (4+4-5) bytes from 5 to 7.
2) About the change around line 77.
Let dst be (void*)5,
because of lines 50-55, the bytes from 5-7 were already writen.
So the aligned copy is from 8.
Reviewed-by: eugenis
Differential Revision: https://reviews.llvm.org/D94552
82655c1514