Relaxed Memory Model Zoo

Ordering relationships

Strictly weaker than

• Total Store Order (TSO) — ARMv8 allows more reorderings than TSO though it is multi-copy-atomic. The TSO ⊆ ARMv8 containment is a model-level monotonicity argument over different instruction sets, not a cited theorem, so the edge is recorded as litmus-grade (provisional): the one-sided witness does not by itself exclude incomparability.

Strictly stronger than

• ARM Memory Model — ARMv7 is non-MCA and weaker than ARMv8.

Compilation target of

• Intermediate Memory Model (IMM) — IMM compiles correctly to ARMv8.
• Linux Kernel Memory Model (LKMM) — Linux kernel primitives compile correctly to ARMv8/AArch64.

Incomparable with

• RISC-V Weak Memory Ordering (RVWMO) — Both are multi-copy atomic and coincide on every standard litmus family over the common instruction set (verified against herd7's aarch64.cat and riscv.cat). The incomparability is instruction-level: RISC-V's fence.tso (which allows SB) and the RCsc/RCpc atomics differ from ARMv8's. See litmus/incomparable/ARMv8-vs-RVWMO.