Base Integer ISA (RV32I and RV64I) Execution Model: Interview Drills

PROMPT
You observe Instruction count mix, branch density, and CPI breakdown by ALU, load/store, branch, and control-transfer classes. on Base Integer ISA (RV32I and RV64I) Execution Model. Walk through root cause and release decision.

STRONG ANSWER
1. Defines workload and earliest failing mechanism.
2. Explains mechanism: The base integer ISA defines a clean load/store architecture: arithmetic and logical operations act only on registers, while memory is accessed through explicit load and store instructions. RV32I and RV64I share the same core design philosophy, with RV64I widening register and address operations and adding word-specific variants for 32-bit subword behavior. The ISA keeps the architectural state intentionally small and regular (32 integer registers plus program counter), making decode and hazard handling straightforward in simple pipelines while still scaling to out-of-order designs. Control flow is formed by conditional branches and jumps with well-defined PC-relative semantics, and the system model separates user-visible instructions from privileged behavior so implementations can reuse the base frontend across microcontrollers, Linux-capable cores, and accelerator-adjacent control processors.
3. Requests proving artifact: Base ISA execution map covering instruction classes, dataflow constraints, and implementation implications from single-cycle to superscalar pipelines.
4. Proposes bounded fix + owner + rollback-safe validation.

WEAK ANSWER
Suggests generic optimization ideas without mechanism proof or owner accountability.

RISC-V EVIDENCE MATRIX - Base Integer ISA (RV32I and RV64I) Execution Model

+--------------------------+--------------------------------+--------------------------------+---------------------------+
| Evidence                 | Tells you                      | Does not prove                 | Next action               |
+--------------------------+--------------------------------+--------------------------------+---------------------------+
| perf counter timeline    | where regression appears       | exact mechanism causality      | correlate with trace      |
| decode/control dump      | control intent per instruction | pipeline side-effect ordering  | inspect retire semantics  |
| trap + CSR logs          | privilege/fault behavior       | performance bottleneck alone   | pair with CPI buckets     |
| MMU/TLB walk trace       | translation behavior           | full system QoS impact         | test mixed workloads      |
| post-fix trend graph     | movement after fix             | long-term stability            | run stress matrix         |
+--------------------------+--------------------------------+--------------------------------+---------------------------+