Large Python bitvector workloads were hitting a sharp performance cliff
during `Solver.add(...)`, consistent with severe hash-table clustering
in expression-heavy assertion paths. The issue was sensitive to input
size/alignment, indicating weak low-bit dispersion in hash combination.
- **Hash mixing update (`src/util/hash.h`)**
- Replaced the old `combine_hash(h1, h2)` arithmetic/xor sequence with
stronger mixing:
- boost-style combine step
- `hash_u(...)` finalization
- Goal: improve low-bit entropy used by chained hash-table bucket
selection under aligned/high-volume AST patterns.
- **Regression guard and A/B comparison (`src/test/chashtable.cpp`)**
- Added `tst_combine_hash_low_bits()` and invoked it from
`tst_chashtable()`.
- The test stresses aligned first components (`i << 12`) combined with a
fixed seed.
- Added an in-test comparison between the **old** and **new** pairwise
hash combiners and validates:
- reduced collision counts for low-bit projections (8-bit and 16-bit
suffixes),
- improved low-bit uniformity for 8-bit and 16-bit suffixes,
- reported prefix/suffix uniformity metrics (high/low 8 and 16 bits) for
visibility in test output.
```cpp
static inline unsigned combine_hash(unsigned h1, unsigned h2) {
h1 ^= h2 + 0x9e3779b9 + (h1 << 6) + (h1 >> 2);
return hash_u(h1);
}
```
---------
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
* Introduce X-macro-based trace tag definition
- Created trace_tags.def to centralize TRACE tag definitions
- Each tag includes a symbolic name and description
- Set up enum class TraceTag for type-safe usage in TRACE macros
* Add script to generate Markdown documentation from trace_tags.def
- Python script parses trace_tags.def and outputs trace_tags.md
* Refactor TRACE_NEW to prepend TraceTag and pass enum to is_trace_enabled
* trace: improve trace tag handling system with hierarchical tagging
- Introduce hierarchical tag-class structure: enabling a tag class activates all child tags
- Unify TRACE, STRACE, SCTRACE, and CTRACE under enum TraceTag
- Implement initial version of trace_tag.def using X(tag, tag_class, description)
(class names and descriptions to be refined in a future update)
* trace: replace all string-based TRACE tags with enum TraceTag
- Migrated all TRACE, STRACE, SCTRACE, and CTRACE macros to use enum TraceTag values instead of raw string literals
* trace : add cstring header
* trace : Add Markdown documentation generation from trace_tags.def via mk_api_doc.py
* trace : rename macro parameter 'class' to 'tag_class' and remove Unicode comment in trace_tags.h.
* trace : Add TODO comment for future implementation of tag_class activation
* trace : Disable code related to tag_class until implementation is ready (#7663).
