x64: Drop the REX prefix in a few more cases #11022
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This commit fixes a few cases where a REX prefix is emitted for an instruction but was not actually required. The REX prefix is unconditionally emitted in situations where 8-bit registers are referenced and one of the registers referenced has an encoding between 4-7. This logic was mistakenly applied to addressing modes as well, however, where 8-bit registers are not referenced and instead 64-bit registers are used. This commit adds a few comments, refactors a few things, and makes it such that "special registers" are not tested for operands to addressing modes (e.g. the base register).
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This commit fixes a few cases where a REX prefix is emitted for an instruction but was not actually required. The REX prefix is unconditionally emitted in situations where 8-bit registers are referenced and one of the registers referenced has an encoding between 4-7. This logic was mistakenly applied to addressing modes as well, however, where 8-bit registers are not referenced and instead 64-bit registers are used.
This commit adds a few comments, refactors a few things, and makes it such that "special registers" are not tested for operands to addressing modes (e.g. the base register).