Does NTL.P1 change the result of the next load/store?
No. It does not alter the architecturally visible effects of the target instruction.
NTL.P1
RISC-V NTL.P1 Instruction Details
Instruction ManualI-typeZihintntl private L1 non-temporal locality hint for the immediately following explicit memory-access target instruction.
Instruction Syntax
ntl.p1
Operand Breakdown
Destination rd: general-purpose register receiving the result.
Source rs1: register holding the first operand.
Immediate imm: 12-bit signed value, sign-extended before operation with rs1.
ZihintntlMicroarch HintsCache & Sync
Instruction Behavior
NTL.P1 is a Zihintntl non-temporal locality HINT encoded as ADD x0, x0, x2. It indicates that the explicit memory accesses of the immediately following target instruction the target instruction is not expected to have temporal locality within the innermost private cache. The hint changes no architectural state and does not alter the architecturally visible effects of the target instruction; implementations may freely ignore it. NTL affects explicit memory-access instructions except Zicbom cache-management instructions, and it can also affect Zicbop prefetch hints.
Quick Understanding & Search Notes
NTL.P1 is a non-temporal locality prefix HINT that describes expected reuse of the next explicit memory access, without changing that access's architectural semantics.
The four NTL variants differ only in cache-level scope: P1, PALL, S1, and ALL.
If the target instruction traps, the official recommendation is not to apply the NTL to the first instruction in the trap handler.
Common Usage Scenarios
Cache & Hints
Understand this scenario with real code like «ntl.p1».
Concurrency & Multi-core
Understand this scenario with real code like «ntl.p1».
Performance
Understand this scenario with real code like «ntl.p1».
Pre-Use Checklist
Syntax Check
- Confirm the current instruction format is I-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
It applies only to the immediately following target instruction; later memory accesses are not governed by this NTL prefix.
This is a HINT and may be ignored; it must not be used as a correctness, synchronization, or consistency mechanism.
The official text discourages following NTL with an instruction that does not explicitly access memory; doing so has no architecturally visible effect but may reduce performance.
NTL does not affect Zicbom CBO.CLEAN/CBO.FLUSH/CBO.INVAL, but can affect other explicit memory accesses and prefetch hints.
FAQ
Can NTL.P1 be ignored by an implementation?
Yes. It is a HINT, so software cannot rely on it for performance or correctness guarantees.