Due to the way the ModRM encoding works on x86, memory addressing
combinations involving RBP or R13 need an additional byte for an 8-bit
displacement of zero.
However, this was also applied in cases where it is unnecessary,
effectively wasting a byte.
- MatR with RSP or R12
8B 44 24 00 mov eax,dword ptr [rsp]
8B 04 24 mov eax,dword ptr [rsp]
- MRegSum with base != RBP or R13
46 8D 7C 37 00 lea r15d,[rdi+r14]
46 8D 3C 37 lea r15d,[rdi+r14]
- MComplex without offset
8B 4C CA 00 mov ecx,dword ptr [rdx+rcx*8]
8B 0C CA mov ecx,dword ptr [rdx+rcx*8]
cde3a3b448