Guide and override compiler optimizations
Overview
This question evaluates a candidate's competency in low-level performance engineering and compiler optimization techniques—covering pragmas, intrinsics, manual code transformations, profiling and correctness verification—within the System Design and compiler-aware optimization domain.
Anthropic
Sep 6, 2025, 12:00 AM
Software Engineer
Onsite
System Design
0
0
Guiding a Compiler for a VLIW-like Backend
You are optimizing hot loops for a VLIW-like target (e.g., DSP/AI accelerator) where the compiler sometimes mis-schedules or over-optimizes. Describe a pragmatic workflow for:
-
Guiding the compiler using:
- Pragmas/directives (e.g., unroll, vectorize, pipeline, ivdep).
- Intrinsics and builtins (vector ops, prefetch, assumes/alignment hints).
- Type/qualifier hints (restrict, const, alignment attributes).
- Compiler flags and function attributes (optimization levels, math/aliasing flags, inlining, target features).
-
When to escalate to manual transformations:
- Manual loop unrolling.
- Software pipelining (modulo scheduling by hand or directives).
- Inline assembly for specific instructions or scheduling control.
-
How to measure impact safely and repeatably:
- Preventing dead-code elimination, warming up, pinning, perf counters.
- Disassembly and compiler optimization reports.
- Guardrails to ensure correctness while changing flags/annotations.
-
Risks and mitigations:
- Undefined behavior, strict aliasing violations, alignment and math semantics.
- Portability across compilers/architectures.
- Debuggability and long-term maintainability.
State concrete tactics, trade-offs, and validation steps. Illustrate with a simple loop example if helpful.
Solution
Login required
Show