Replace optional<unique_ptr> with unique_ptr for heuristics

[wujingyue]

Summary: std::optional<std::unique_ptr<T>> is redundant since unique_ptr can represent "no value" via nullptr.

Changes:

• getMaybeHeuristicsFor / getMaybeHeuristicParams now return std::unique_ptr<T> (nullptr when unavailable).
• Call sites: .has_value() → != nullptr, removed valueOrError for heuristics path.
• FusionKernelRuntime constructor uses NVF_ERROR(heuristics_ != nullptr) after getMaybeHeuristicsFor.

Files: fusion_kernel_runtime.{h,cpp}, fusion_segmenter.{h,cpp}, fusion_executor_cache.cpp, benchmarks (heuristic_*.cpp, shape_inference.cpp).

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[greptile-apps]

Greptile Summary

This PR refactors the heuristics API by removing the redundant std::optional<std::unique_ptr<T>> pattern and replacing it with std::unique_ptr<T>, using nullptr to represent "no value". The changes are:

• getMaybeHeuristicsFor now returns std::unique_ptr<HeuristicParamsList> (instead of std::optional<std::unique_ptr<...>>)
• getMaybeHeuristicParams now returns std::unique_ptr<HeuristicParams> (instead of std::optional<std::unique_ptr<...>>)
• Call sites updated: .has_value() → != nullptr, .value() removed
• FusionKernelRuntime constructor uses NVF_ERROR(heuristics_ != nullptr) instead of valueOrError
• Benchmark files updated to use nullptr checks

The refactoring is straightforward and improves code clarity by eliminating the double-indirection pattern.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The refactoring is mechanical and straightforward - replacing std::optional<std::unique_ptr<T>> with std::unique_ptr<T> is a well-understood C++ pattern improvement. All call sites have been consistently updated, and the semantics remain identical (nullptr represents "no value" in both cases)
• No files require special attention

Important Files Changed

Filename	Overview
csrc/runtime/fusion_kernel_runtime.h	Updated getMaybeHeuristicsFor signature to return std::unique_ptr<HeuristicParamsList> instead of std::optional<std::unique_ptr<...>>, with updated documentation
csrc/runtime/fusion_kernel_runtime.cpp	Refactored to return nullptr instead of std::nullopt, replaced valueOrError with direct nullptr check at constructor callsite
csrc/fusion_segmenter.h	Updated getMaybeHeuristicParams signature to return std::unique_ptr<HeuristicParams> with updated documentation
csrc/fusion_segmenter.cpp	Changed return type and replaced std::nullopt with nullptr
csrc/runtime/fusion_executor_cache.cpp	Simplified lambda to directly assign return value and check for nullptr instead of checking .has_value() and extracting with .value()
benchmarks/cpp/heuristic_cache.cpp	Updated assertions to use != nullptr instead of .has_value()
benchmarks/cpp/heuristic_lookup.cpp	Updated assertions to use != nullptr instead of .has_value()
benchmarks/cpp/shape_inference.cpp	Updated assertions to use != nullptr instead of .has_value()

_{Last reviewed commit: 2558dc5}

[greptile-apps]

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[github-actions]

Description

• Replace std::optional<std::unique_ptr<T>> with std::unique_ptr<T> for heuristics

• Update function signatures: getMaybeHeuristicsFor and getMaybeHeuristicParams now return unique_ptr directly

• Modify call sites: .has_value() checks changed to != nullptr, removed .valueOrError() calls

• Add null pointer validation with NVF_ERROR(heuristics_ != nullptr) in FusionKernelRuntime constructor

Changes walkthrough

Relevant files

Enhancement

heuristic_cache.cpp Update heuristic cache benchmark null checks                          benchmarks/cpp/heuristic_cache.cpp Changed .has_value() to != nullptr checks in benchmark functions Updated NVF_ERROR assertions to use null pointer comparison +2/-2      heuristic_lookup.cpp Update heuristic lookup benchmark null checks                        benchmarks/cpp/heuristic_lookup.cpp Changed .has_value() to != nullptr checks in benchmark functions Updated NVF_ERROR assertions to use null pointer comparison +2/-2      shape_inference.cpp Update shape inference benchmark null checks                          benchmarks/cpp/shape_inference.cpp Changed .has_value() to != nullptr checks in shape inference functions Updated NVF_ERROR assertions to use null pointer comparison +2/-2      fusion_segmenter.cpp Update getMaybeHeuristicParams return type and null handling csrc/fusion_segmenter.cpp Changed return type from std::optional> to std::unique_ptr Changed return std::nullopt; to return nullptr; when scheduling unavailable +3/-3      fusion_executor_cache.cpp Simplify kernel runtime reuse logic                                            csrc/runtime/fusion_executor_cache.cpp Simplified kernel runtime reuse logic to use direct null pointer check Removed unnecessary optional wrapping and unwrapping of heuristics +2/-6      fusion_kernel_runtime.cpp Update getMaybeHeuristicParams return type and constructor validation csrc/runtime/fusion_kernel_runtime.cpp Changed return type from std::optional> to std::unique_ptr Updated constructor to use direct null pointer check instead of valueOrError Added NVF_ERROR(heuristics_ != nullptr) validation Changed return std::nullopt; to return nullptr; when heuristics unavailable +11/-13  fusion_segmenter.h Update SegmentedGroup getMaybeHeuristicParams signature    csrc/fusion_segmenter.h Updated function signature from std::optional> to std::unique_ptr Updated documentation to reflect nullptr instead of nullopt return +2/-2      fusion_kernel_runtime.h Update FusionKernelRuntime getMaybeHeuristicsFor signature csrc/runtime/fusion_kernel_runtime.h Updated function signature from std::optional> to std::unique_ptr Updated documentation to reflect nullptr instead of nullopt return +3/-3

PR Reviewer Guide

Here are some key observations to aid the review process:

🧪 No relevant tests

🔒 No security concerns identified

⚡ Recommended focus areas for review

Logic Error in Kernel Reuse In the kernel runtime reuse logic, the lambda captures new_heuristics by reference but then assigns to it inside the lambda. However, the assignment new_heuristics = kernel_runtime->getMaybeHeuristicsFor(...) happens after the return statement, making it unreachable. This breaks the kernel reuse functionality as new_heuristics will never be populated with the found runtime's heuristics. if (!isOptionDisabled(DisableOption::KernelReuse)) { FUSER_PERF_SCOPE("FusionExecutorCache::getKernelRuntimeFor::reuseKRT"); auto runtime_it = std::find_if( kernel_runtimes.begin(), kernel_runtimes.end(), [&args, &new_heuristics, &forced_index_type](auto& kernel_runtime) { new_heuristics = kernel_runtime->getMaybeHeuristicsFor(args, forced_index_type); return new_heuristics != nullptr; });