[V4] Slab stack No.2

[ConorWilliams]

Summary by CodeRabbit

• New Features

  • Introduced slab_stack, a fixed-size, single-slab user-space stack implementation for memory allocation.
  • Extended benchmarks to include slab_stack variants.

• Bug Fixes

  • Fixed const-correctness in geometric_stack method signature.
  • Corrected typo in comment.

• Tests

  • Added comprehensive test coverage for slab_stack across multiple scenarios, including allocation limits and checkpoint/acquire/release cycles.

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Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@src/batteries/slab_stack.cxx`:
- Around line 109-114: The push() routine currently does pointer arithmetic
diff_type free_bytes = node_size * (m_hi - m_sp) which is UB if init_slab failed
in release() leaving m_ctrl/m_lo/m_sp/m_hi == nullptr; modify push() to first
check that m_hi and m_sp are non-null (e.g., if (m_hi == nullptr || m_sp ==
nullptr) throw std::bad_alloc{} or handle as out-of-space) before performing
m_hi - m_sp, and apply the same null-safety check in the analogous location
around lines 158-163; also update the comment in release() to note that pointers
are cleared and that callers must handle null pointer state so subsequent
pointer arithmetic is guarded.

In `@test/src/stack.cpp`:
- Around line 129-137: Wrap tests that depend on exceptions with conditional
compilation and avoid catching std::bad_alloc for stacks that allocate
dynamically: enclose the entire "slab_stack - throws when full" test in `#if`
LF_COMPILER_EXCEPTIONS ... `#endif`, and in the TEMPLATE_TEST_CASEs that iterate
over geometric_stack, adaptor_stack and slab_stack, remove or guard the
try/catch(std::bad_alloc) blocks with `#if` LF_COMPILER_EXCEPTIONS so only
slab_stack is allowed to trigger and catch bad_alloc; alternatively use
type-specific branches (e.g., if constexpr or trait for fixed_capacity_stack) to
only perform exception-based early-exit logic for slab_stack and use standard
allocation failure checks for geometric_stack/adaptor_stack.

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Fix all unresolved CodeRabbit comments on this PR:

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• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

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📥 Commits

Reviewing files that changed from the base of the PR and between 387d763 and d493533.

📒 Files selected for processing (6)

• CMakeLists.txt
• benchmark/src/libfork_benchmark/fib/libfork.cpp
• src/batteries/batteries.cxx
• src/batteries/geometric_stack.cxx
• src/batteries/slab_stack.cxx
• test/src/stack.cpp