Benchmark devirt on real-world dispatch: tantivy 3.5× faster, tracing ~0%

Cargo.toml

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 [workspace]
 members = ["crates/*", "fuzz"]
+exclude = ["benchmarks"]
 resolver = "3"
 
 [workspace.package]

benchmarks/.gitignore

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+target/
+Cargo.lock

benchmarks/README.md

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+# Real-World Devirt Benchmarks
+
+Benchmarks measuring `devirt`'s impact on dispatch patterns from real Rust projects.
+
+## tantivy search engine — scorer dispatch (`tantivy-devirt/`)
+
+Reproduces tantivy's per-document scoring loop. tantivy iterates over
+matching documents calling `scorer.score()` (BM25: ~10 arithmetic ops)
+and `scorer.advance()` through `&mut dyn Scorer` — mandatory dynamic
+dispatch since the scorer type comes from the user's search query parsed
+at runtime.
+
+Reference: [tantivy `src/query/weight.rs`](https://github.com/quickwit-oss/tantivy/blob/main/src/query/weight.rs)
+
+Note: tantivy already manually devirtualizes its hottest paths
+(`TermWeight::for_each` calls the concrete `TermScorer` directly).
+The `dyn Scorer` fallback runs for uncommon query types (phrase, regex,
+fuzzy). This benchmark measures the speedup devirt would provide on that
+fallback path, and demonstrates what tantivy achieves manually that devirt
+could automate.
+
+### Results (TermScorer with BM25 scoring)
+
+| n documents | devirt | plain vtable | Speedup |
+|-------------|--------|-------------|---------|
+| 1,000 | 3.1 µs | 9.9 µs | **3.2×** |
+| 10,000 | 27.8 µs | 98.9 µs | **3.6×** |
+| 100,000 | 276 µs | 961 µs | **3.5×** |
+| 1,000,000 | 3.54 ms | 10.3 ms | **2.9×** |
+
+Shuffled 80/20 hot/cold (100 scorers × 1000 docs): 333 µs vs 821 µs — **2.5×**
+
+### Running
+
+```bash
+cd benchmarks/tantivy-devirt
+cargo bench
+```

benchmarks/tantivy-devirt/Cargo.toml

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+[package]
+name = "tantivy-devirt-bench"
+version = "0.0.0"
+edition = "2024"
+publish = false
+
+[dependencies]
+devirt = { path = "../../crates/core" }
+
+[dev-dependencies]
+criterion = { version = "0.5", features = ["html_reports"] }
+
+[[bench]]
+name = "scorer"
+harness = false
+
+[profile.bench]
+lto = "thin"
+codegen-units = 1