i#1569 AArch64: Implement move (immediate) to zero register. #2423
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Moving a value to the zero register is a no-op but we have seen
ADR XZR,... used by Node.js (libv8). Having these API functions,
instrlist_insert_mov_{immed_ptrsz,instr_addr}, create no instructions
potentially adds a case for the caller to handle but most uses of
those functions set the last two arguments to NULL in any case. If it
were a problem we could create a NOP instruction instead. Creating
actual moves to XZR seems less good and would be awkward if in
generating a constant value we ever used instructions that cannot
target XZR.
Change-Id: I2791410d5b463906ddbc1f62e4d0f9023eb84633
derekbruening
approved these changes
May 9, 2017
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Moving a value to the zero register is a no-op but we have seen
ADR XZR,... used by Node.js (libv8). Having these API functions,
instrlist_insert_mov_{immed_ptrsz,instr_addr}, create no instructions
potentially adds a case for the caller to handle but most uses of
those functions set the last two arguments to NULL in any case. If it
were a problem we could create a NOP instruction instead. Creating
actual moves to XZR seems less good and would be awkward if in
generating a constant value we ever used instructions that cannot
target XZR.