feat(allocs): add callsite tracking for allocations

.cargo/config.toml

@@ -6,7 +6,7 @@ codecov = "llvm-cov --workspace --ignore-filename-regex tasks"
 coverage = "run -p oxc_coverage --profile coverage --"
 benchmark = "bench -p oxc_benchmark"
 minsize = "run -p oxc_minsize --profile coverage --"
-allocs = "run -p oxc_track_memory_allocations --profile coverage --"
+allocs = "run -p oxc_track_memory_allocations --profile coverage-with-debug --"
 rule = "run -p rulegen"
 
 # Build oxlint in release mode

Cargo.toml

@@ -284,6 +284,12 @@ lto = "thin" # Faster compile time with thin LTO
 debug-assertions = true # Make sure `debug_assert!`s pass
 overflow-checks = true # Catch arithmetic overflow errors
 
+# Same as `coverage`, but with debug symbols included for backtraces.
+[profile.coverage-with-debug]
+inherits = "coverage"
+strip = false # Keep debug information in binary
+debug = true # Include maximum amount of debug information
+
 # Profile for linting with release mode-like settings.
 # Catches lint errors which only appear in release mode.
 # `cargo lint --profile dev-no-debug-assertions` is about 35% faster than `cargo lint --release`.

tasks/track_memory_allocations/Cargo.toml

@@ -23,6 +23,7 @@ oxc_parser = { workspace = true }
 oxc_semantic = { workspace = true }
 oxc_tasks_common = { workspace = true }
 
+backtrace = "0.3"
 humansize = { workspace = true }
 mimalloc-safe = { workspace = true }
 

tasks/track_memory_allocations/README.md

@@ -1,3 +1,27 @@
 # Oxc allocations stats
 
 This task keeps track of the number of system allocations as well as arena allocations and the total number of bytes allocated. This is used for monitoring possible regressions in allocations and improvements in memory usage.
+
+## Callsite aggregation (optional)
+
+You can also aggregate where allocations occur by source location, similar in spirit to dhat-rs. This is disabled by default because collecting backtraces for every allocation is expensive.
+
+- Enable tracking: set `OXC_ALLOC_SITES=1`
+- Optional sampling to reduce overhead: set `OXC_ALLOC_SAMPLE=N` to record 1 in `N` allocations (default `1000`).
+
+Example:
+
+```
+OXC_ALLOC_SITES=1 OXC_ALLOC_SAMPLE=100 cargo run -p oxc_track_memory_allocations
+```
+
+At the end of the run, you'll see a "Top allocation sites" section like:
+
+```
+Top allocation sites (sampled 1 in 100)
+Location                               | Allocations
+----------------------------------------------------
+crates/oxc_parser/src/lexer.rs:123     |         152
+crates/oxc_semantic/src/builder.rs:45  |         101
+...
+```