Does MOP.RR.2 write rd by default?
Yes. The official Zimop rule says it writes zero to rd by default.
MOP.RR.2
RISC-V MOP.RR.2 Instruction Details
Instruction ManualR-typeZimop MOP.RR.2; by default writes zero to rd and may be redefined to read rs1/rs2 and write rd.
Instruction Syntax
mop.rr.2 rd, rs1, rs2
Operand Breakdown
Destination rd: register receiving the operation result.
Source rs1: register holding the first operand.
Source rs2: register holding the second operand.
ZimopSystem & Privileged
Instruction Behavior
MOP.RR.2 is a Zimop may-be-operation with recommended syntax mop.rr.2 rd, rs1, rs2. If no other extension redefines the encoding, the official default behavior writes 0 to x[rd]. The encoding space allows future extensions to define it as reading x[rs1] and x[rs2] and writing x[rd]. Standard software should not execute a MOP unless deliberately targeting an extension that redefines it.
Quick Understanding & Search Notes
MOP.RR.2 is a three-register Zimop MOP encoding; when not redefined, it writes zero to rd.
The official extension defines 8 MOP.RR.n instructions numbered 0 through 7.
MOP.RR.n allows a future extension to read rs1/rs2 and write rd, but by default it reads no source registers and creates no source-to-destination syntactic dependency.
Common Usage Scenarios
System & Privileged
Understand this scenario with real code like «mop.rr.2 t0, t1, t2».
Extension Compatibility
Understand this scenario with real code like «mop.rr.2 t0, t1, t2».
Pre-Use Checklist
Syntax Check
- Confirm the current instruction format is R-type.
- Confirm the operand order matches the example.
Semantic Check
- Ensure the destination register usage is compatible with the calling convention.
- Confirm this is not the lower-level form of a pseudo-instruction expansion.
Pitfalls / Common Confusions
The default is not a true no-register-write NOP; MOP.RR.n writes zero to rd by default.
Default Zimop MOPs carry no syntactic dependency from rs1/rs2 to rd; a redefining extension may specify otherwise.
Zimop defines only MOP.RR.0 through MOP.RR.7.
FAQ
How is MOP.RR.2 different from MOP.R.2?
MOP.RR is reserved for future extensions that may read two source registers; MOP.R is reserved for future extensions that may read one source register.