x64Emitter: Avoid 8-bit displacement when possible #8556
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Test the behavior of OpArg::WriteRest by using MOV with the various addressing modes (MatR, MRegSum, etc.) in the source operand. Both the instruction and the instruction length are validated.
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]
Shorter, displacement is now handled in one location.
TODO was already taken care of in PR dolphin-emu#941.
No users, and one them seems to do the same as stddef.h's offsetof() already used elsewhere.
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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.
This PR adds some tests, fixes the issue, refactors the relevant function, and cleans up some unrelated minor things in the neighborhood.