Profiling

Perf profiling:

Tools that can be used to generate/ visualise perf results:

Example using perf on micro_bench_ops and visualising using flamescope:

  1. # build `examples/micro_bench_ops`
  2. cargo build --release --example micro_bench_ops
  4. # run `examples/micro_bench_ops` using perf
  5. sudo perf record -F 49 -a -g -- ./target/release/examples/micro_bench_ops
  6. sudo perf script --header > micro_bench_ops_perf
  8. # now open the file using flamescope

Example running deno_tcp.ts in combination with flamegraph (script.sh):

  1. sudo flamegraph -o flamegraph.svg target/debug/deno run --allow-net cli/bench/deno_tcp.ts &
  2. sleep 1
  3. ./third_party/prebuilt/linux64/wrk http://localhost:4500/
  4. sleep 1
  5. kill `pgrep perf`

v8 profiling:

Example using v8 profiling on micro_bench_ops:

  1. # build `examples/micro_bench_ops`
  2. cargo build --release --example micro_bench_ops
  4. # run `examples/micro_bench_ops`
  5. ./target/release/examples/micro_bench_ops --prof

Example using v8 profiling on deno_tcp.ts:

  1. # build `deno`
  2. cargo build --release
  4. # run `deno_tcp.ts`
  5. ./target/release/deno --v8-flags=--prof --allow-net cli/bench/deno_tcp.ts &
  6. sleep 1
  7. ./third_party/prebuilt/linux64/wrk http://localhost:4500/
  8. sleep 1
  9. kill `pgrep deno`

V8 will write a file in the current directory that looks like this: isolate-0x7fad98242400-v8.log. To examine this file:

  1. node --prof-process isolate-0x7fad98242400-v8.log > prof.log

prof.log will contain information about tick distribution of different calls.

To view the log with Web UI, generate JSON file of the log:

Open rusty_v8/v8/tools/profview/index.html in your browser, and select prof.json to view the distribution graphically.

Useful V8 flags during profiling:

  • —prof
  • —log-internal-timer-events
  • —log-timer-events
  • —track-gc
  • —log-source-code
  • —track-gc-object-stats

To learn more about profiling, check out the following links:

Debugging with LLDB

To debug the deno binary, we can use rust-lldb. It should come with rustc and is a wrapper around LLDB.

  1. $ rust-lldb -- ./target/debug/deno run --allow-net tests/http_bench.ts
  2. # On macOS, you might get warnings like
  3. # `ImportError: cannot import name _remove_dead_weakref`
  4. # In that case, use system python by setting PATH, e.g.
  5. # PATH=/System/Library/Frameworks/Python.framework/Versions/2.7/bin:$PATH
  6. (lldb) command script import "/Users/kevinqian/.rustup/toolchains/1.36.0-x86_64-apple-darwin/lib/rustlib/etc/lldb_rust_formatters.py"
  7. (lldb) type summary add --no-value --python-function lldb_rust_formatters.print_val -x ".*" --category Rust
  8. (lldb) type category enable Rust
  9. (lldb) target create "../deno/target/debug/deno"
  10. Current executable set to '../deno/target/debug/deno' (x86_64).
  11. (lldb) settings set -- target.run-args  "tests/http_bench.ts" "--allow-net"
  12. (lldb) b op_start
  13. (lldb) r

V8 flags

V8 has many many internal command-line flags:

  1. $ deno run --v8-flags=--help _
  2. SSE3=1 SSSE3=1 SSE4_1=1 SSE4_2=1 SAHF=1 AVX=1 FMA3=1 BMI1=1 BMI2=1 LZCNT=1 POPCNT=1 ATOM=0
  3. Synopsis:
  4.   shell [options] [--shell] [<file>...]
  5.   d8 [options] [-e <string>] [--shell] [[--module] <file>...]
  7.   -e        execute a string in V8
  8.   --shell   run an interactive JavaScript shell
  9.   --module  execute a file as a JavaScript module
  11. Note: the --module option is implicitly enabled for *.mjs files.
  13. The following syntax for options is accepted (both '-' and '--' are ok):
  14.   --flag        (bool flags only)
  15.   --no-flag     (bool flags only)
  16.   --flag=value  (non-bool flags only, no spaces around '=')
  17.   --flag value  (non-bool flags only)
  18.   --            (captures all remaining args in JavaScript)
  20. Options:
  21.   --use-strict (enforce strict mode)
  22.         type: bool  default: false
  23.   --es-staging (enable test-worthy harmony features (for internal use only))
  24.         type: bool  default: false
  25.   --harmony (enable all completed harmony features)
  26.         type: bool  default: false
  27.   --harmony-shipping (enable all shipped harmony features)
  28.         type: bool  default: true
  29.   --harmony-regexp-sequence (enable "RegExp Unicode sequence properties" (in progress))
  30.         type: bool  default: false
  31.   --harmony-weak-refs-with-cleanup-some (enable "harmony weak references with FinalizationRegistry.prototype.cleanupSome" (in progress))
  32.         type: bool  default: false
  33.   --harmony-regexp-match-indices (enable "harmony regexp match indices" (in progress))
  34.         type: bool  default: false
  35.   --harmony-top-level-await (enable "harmony top level await")
  36.         type: bool  default: false
  37.   --harmony-namespace-exports (enable "harmony namespace exports (export * as foo from 'bar')")
  38.         type: bool  default: true
  39.   --harmony-sharedarraybuffer (enable "harmony sharedarraybuffer")
  40.         type: bool  default: true
  41.   --harmony-import-meta (enable "harmony import.meta property")
  42.         type: bool  default: true
  43.   --harmony-dynamic-import (enable "harmony dynamic import")
  44.         type: bool  default: true
  45.   --harmony-promise-all-settled (enable "harmony Promise.allSettled")
  46.         type: bool  default: true
  47.   --harmony-promise-any (enable "harmony Promise.any")
  48.         type: bool  default: true
  49.   --harmony-private-methods (enable "harmony private methods in class literals")
  50.         type: bool  default: true
  51.   --harmony-weak-refs (enable "harmony weak references")
  52.         type: bool  default: true
  53.   --harmony-string-replaceall (enable "harmony String.prototype.replaceAll")
  54.         type: bool  default: true
  55.   --harmony-logical-assignment (enable "harmony logical assignment")
  56.         type: bool  default: true
  57.   --lite-mode (enables trade-off of performance for memory savings)
  58.         type: bool  default: false
  59.   --future (Implies all staged features that we want to ship in the not-too-far future)
  60.         type: bool  default: false
  61.   --assert-types (generate runtime type assertions to test the typer)
  62.         type: bool  default: false
  63.   --allocation-site-pretenuring (pretenure with allocation sites)
  64.         type: bool  default: true
  65.   --page-promotion (promote pages based on utilization)
  66.         type: bool  default: true
  67.   --always-promote-young-mc (always promote young objects during mark-compact)
  68.         type: bool  default: true
  69.   --page-promotion-threshold (min percentage of live bytes on a page to enable fast evacuation)
  70.         type: int  default: 70
  71.   --trace-pretenuring (trace pretenuring decisions of HAllocate instructions)
  72.         type: bool  default: false
  73.   --trace-pretenuring-statistics (trace allocation site pretenuring statistics)
  74.         type: bool  default: false
  75.   --track-fields (track fields with only smi values)
  76.         type: bool  default: true
  77.   --track-double-fields (track fields with double values)
  78.         type: bool  default: true
  79.   --track-heap-object-fields (track fields with heap values)
  80.         type: bool  default: true
  81.   --track-computed-fields (track computed boilerplate fields)
  82.         type: bool  default: true
  83.   --track-field-types (track field types)
  84.         type: bool  default: true
  85.   --trace-block-coverage (trace collected block coverage information)
  86.         type: bool  default: false
  87.   --trace-protector-invalidation (trace protector cell invalidations)
  88.         type: bool  default: false
  89.   --feedback-normalization (feed back normalization to constructors)
  90.         type: bool  default: false
  91.   --enable-one-shot-optimization (Enable size optimizations for the code that will only be executed once)
  92.         type: bool  default: false
  93.   --unbox-double-arrays (automatically unbox arrays of doubles)
  94.         type: bool  default: true
  95.   --interrupt-budget (interrupt budget which should be used for the profiler counter)
  96.         type: int  default: 147456
  97.   --jitless (Disable runtime allocation of executable memory.)
  98.         type: bool  default: false
  99.   --use-ic (use inline caching)
  100.         type: bool  default: true
  101.   --budget-for-feedback-vector-allocation (The budget in amount of bytecode executed by a function before we decide to allocate feedback vectors)
  102.         type: int  default: 1024
  103.   --lazy-feedback-allocation (Allocate feedback vectors lazily)
  104.         type: bool  default: true
  105.   --ignition-elide-noneffectful-bytecodes (elide bytecodes which won't have any external effect)
  106.         type: bool  default: true
  107.   --ignition-reo (use ignition register equivalence optimizer)
  108.         type: bool  default: true
  109.   --ignition-filter-expression-positions (filter expression positions before the bytecode pipeline)
  110.         type: bool  default: true
  111.   --ignition-share-named-property-feedback (share feedback slots when loading the same named property from the same object)
  112.         type: bool  default: true
  113.   --print-bytecode (print bytecode generated by ignition interpreter)
  114.         type: bool  default: false
  115.   --enable-lazy-source-positions (skip generating source positions during initial compile but regenerate when actually required)
  116.         type: bool  default: true
  117.   --stress-lazy-source-positions (collect lazy source positions immediately after lazy compile)
  118.         type: bool  default: false
  119.   --print-bytecode-filter (filter for selecting which functions to print bytecode)
  120.         type: string  default: *
  121.   --trace-ignition-codegen (trace the codegen of ignition interpreter bytecode handlers)
  122.         type: bool  default: false
  123.   --trace-ignition-dispatches (traces the dispatches to bytecode handlers by the ignition interpreter)
  124.         type: bool  default: false
  125.   --trace-ignition-dispatches-output-file (the file to which the bytecode handler dispatch table is written (by default, the table is not written to a file))
  126.         type: string  default: nullptr
  127.   --fast-math (faster (but maybe less accurate) math functions)
  128.         type: bool  default: true
  129.   --trace-track-allocation-sites (trace the tracking of allocation sites)
  130.         type: bool  default: false
  131.   --trace-migration (trace object migration)
  132.         type: bool  default: false
  133.   --trace-generalization (trace map generalization)
  134.         type: bool  default: false
  135.   --turboprop (enable experimental turboprop mid-tier compiler.)
  136.         type: bool  default: false
  137.   --concurrent-recompilation (optimizing hot functions asynchronously on a separate thread)
  138.         type: bool  default: true
  139.   --trace-concurrent-recompilation (track concurrent recompilation)
  140.         type: bool  default: false
  141.   --concurrent-recompilation-queue-length (the length of the concurrent compilation queue)
  142.         type: int  default: 8
  143.   --concurrent-recompilation-delay (artificial compilation delay in ms)
  144.         type: int  default: 0
  145.   --block-concurrent-recompilation (block queued jobs until released)
  146.         type: bool  default: false
  147.   --concurrent-inlining (run optimizing compiler's inlining phase on a separate thread)
  148.         type: bool  default: false
  149.   --max-serializer-nesting (maximum levels for nesting child serializers)
  150.         type: int  default: 25
  151.   --trace-heap-broker-verbose (trace the heap broker verbosely (all reports))
  152.         type: bool  default: false
  153.   --trace-heap-broker-memory (trace the heap broker memory (refs analysis and zone numbers))
  154.         type: bool  default: false
  155.   --trace-heap-broker (trace the heap broker (reports on missing data only))
  156.         type: bool  default: false
  157.   --stress-runs (number of stress runs)
  158.         type: int  default: 0
  159.   --deopt-every-n-times (deoptimize every n times a deopt point is passed)
  160.         type: int  default: 0
  161.   --print-deopt-stress (print number of possible deopt points)
  162.         type: bool  default: false
  163.   --opt (use adaptive optimizations)
  164.         type: bool  default: true
  165.   --turbo-sp-frame-access (use stack pointer-relative access to frame wherever possible)
  166.         type: bool  default: false
  167.   --turbo-control-flow-aware-allocation (consider control flow while allocating registers)
  168.         type: bool  default: true
  169.   --turbo-filter (optimization filter for TurboFan compiler)
  170.         type: string  default: *
  171.   --trace-turbo (trace generated TurboFan IR)
  172.         type: bool  default: false
  173.   --trace-turbo-path (directory to dump generated TurboFan IR to)
  174.         type: string  default: nullptr
  175.   --trace-turbo-filter (filter for tracing turbofan compilation)
  176.         type: string  default: *
  177.   --trace-turbo-graph (trace generated TurboFan graphs)
  178.         type: bool  default: false
  179.   --trace-turbo-scheduled (trace TurboFan IR with schedule)
  180.         type: bool  default: false
  181.   --trace-turbo-cfg-file (trace turbo cfg graph (for C1 visualizer) to a given file name)
  182.         type: string  default: nullptr
  183.   --trace-turbo-types (trace TurboFan's types)
  184.         type: bool  default: true
  185.   --trace-turbo-scheduler (trace TurboFan's scheduler)
  186.         type: bool  default: false
  187.   --trace-turbo-reduction (trace TurboFan's various reducers)
  188.         type: bool  default: false
  189.   --trace-turbo-trimming (trace TurboFan's graph trimmer)
  190.         type: bool  default: false
  191.   --trace-turbo-jt (trace TurboFan's jump threading)
  192.         type: bool  default: false
  193.   --trace-turbo-ceq (trace TurboFan's control equivalence)
  194.         type: bool  default: false
  195.   --trace-turbo-loop (trace TurboFan's loop optimizations)
  196.         type: bool  default: false
  197.   --trace-turbo-alloc (trace TurboFan's register allocator)
  198.         type: bool  default: false
  199.   --trace-all-uses (trace all use positions)
  200.         type: bool  default: false
  201.   --trace-representation (trace representation types)
  202.         type: bool  default: false
  203.   --turbo-verify (verify TurboFan graphs at each phase)
  204.         type: bool  default: false
  205.   --turbo-verify-machine-graph (verify TurboFan machine graph before instruction selection)
  206.         type: string  default: nullptr
  207.   --trace-verify-csa (trace code stubs verification)
  208.         type: bool  default: false
  209.   --csa-trap-on-node (trigger break point when a node with given id is created in given stub. The format is: StubName,NodeId)
  210.         type: string  default: nullptr
  211.   --turbo-stats (print TurboFan statistics)
  212.         type: bool  default: false
  213.   --turbo-stats-nvp (print TurboFan statistics in machine-readable format)
  214.         type: bool  default: false
  215.   --turbo-stats-wasm (print TurboFan statistics of wasm compilations)
  216.         type: bool  default: false
  217.   --turbo-splitting (split nodes during scheduling in TurboFan)
  218.         type: bool  default: true
  219.   --function-context-specialization (enable function context specialization in TurboFan)
  220.         type: bool  default: false
  221.   --turbo-inlining (enable inlining in TurboFan)
  222.         type: bool  default: true
  223.   --max-inlined-bytecode-size (maximum size of bytecode for a single inlining)
  224.         type: int  default: 500
  225.   --max-inlined-bytecode-size-cumulative (maximum cumulative size of bytecode considered for inlining)
  226.         type: int  default: 1000
  227.   --max-inlined-bytecode-size-absolute (maximum cumulative size of bytecode considered for inlining)
  228.         type: int  default: 5000
  229.   --reserve-inline-budget-scale-factor (maximum cumulative size of bytecode considered for inlining)
  230.         type: float  default: 1.2
  231.   --max-inlined-bytecode-size-small (maximum size of bytecode considered for small function inlining)
  232.         type: int  default: 30
  233.   --max-optimized-bytecode-size (maximum bytecode size to be considered for optimization; too high values may cause the compiler to hit (release) assertions)
  234.         type: int  default: 61440
  235.   --min-inlining-frequency (minimum frequency for inlining)
  236.         type: float  default: 0.15
  237.   --polymorphic-inlining (polymorphic inlining)
  238.         type: bool  default: true
  239.   --stress-inline (set high thresholds for inlining to inline as much as possible)
  240.         type: bool  default: false
  241.   --trace-turbo-inlining (trace TurboFan inlining)
  242.         type: bool  default: false
  243.   --turbo-inline-array-builtins (inline array builtins in TurboFan code)
  244.         type: bool  default: true
  245.   --use-osr (use on-stack replacement)
  246.         type: bool  default: true
  247.   --trace-osr (trace on-stack replacement)
  248.         type: bool  default: false
  249.   --analyze-environment-liveness (analyze liveness of environment slots and zap dead values)
  250.         type: bool  default: true
  251.   --trace-environment-liveness (trace liveness of local variable slots)
  252.         type: bool  default: false
  253.   --turbo-load-elimination (enable load elimination in TurboFan)
  254.         type: bool  default: true
  255.   --trace-turbo-load-elimination (trace TurboFan load elimination)
  256.         type: bool  default: false
  257.   --turbo-profiling (enable basic block profiling in TurboFan)
  258.         type: bool  default: false
  259.   --turbo-profiling-verbose (enable basic block profiling in TurboFan, and include each function's schedule and disassembly in the output)
  260.         type: bool  default: false
  261.   --turbo-verify-allocation (verify register allocation in TurboFan)
  262.         type: bool  default: false
  263.   --turbo-move-optimization (optimize gap moves in TurboFan)
  264.         type: bool  default: true
  265.   --turbo-jt (enable jump threading in TurboFan)
  266.         type: bool  default: true
  267.   --turbo-loop-peeling (Turbofan loop peeling)
  268.         type: bool  default: true
  269.   --turbo-loop-variable (Turbofan loop variable optimization)
  270.         type: bool  default: true
  271.   --turbo-loop-rotation (Turbofan loop rotation)
  272.         type: bool  default: true
  273.   --turbo-cf-optimization (optimize control flow in TurboFan)
  274.         type: bool  default: true
  275.   --turbo-escape (enable escape analysis)
  276.         type: bool  default: true
  277.   --turbo-allocation-folding (Turbofan allocation folding)
  278.         type: bool  default: true
  279.   --turbo-instruction-scheduling (enable instruction scheduling in TurboFan)
  280.         type: bool  default: false
  281.   --turbo-stress-instruction-scheduling (randomly schedule instructions to stress dependency tracking)
  282.         type: bool  default: false
  283.   --turbo-store-elimination (enable store-store elimination in TurboFan)
  284.         type: bool  default: true
  285.   --trace-store-elimination (trace store elimination)
  286.         type: bool  default: false
  287.   --turbo-rewrite-far-jumps (rewrite far to near jumps (ia32,x64))
  288.         type: bool  default: true
  289.   --stress-gc-during-compilation (simulate GC/compiler thread race related to https://crbug.com/v8/8520)
  290.         type: bool  default: false
  291.   --turbo-fast-api-calls (enable fast API calls from TurboFan)
  292.         type: bool  default: false
  293.   --reuse-opt-code-count (don't discard optimized code for the specified number of deopts.)
  294.         type: int  default: 0
  295.   --turbo-nci (enable experimental native context independent code.)
  296.         type: bool  default: false
  297.   --turbo-nci-as-highest-tier (replace default TF with NCI code as the highest tier for testing purposes.)
  298.         type: bool  default: false
  299.   --print-nci-code (print native context independent code.)
  300.         type: bool  default: false
  301.   --trace-turbo-nci (trace native context independent code.)
  302.         type: bool  default: false
  303.   --turbo-collect-feedback-in-generic-lowering (enable experimental feedback collection in generic lowering.)
  304.         type: bool  default: false
  305.   --optimize-for-size (Enables optimizations which favor memory size over execution speed)
  306.         type: bool  default: false
  307.   --untrusted-code-mitigations (Enable mitigations for executing untrusted code)
  308.         type: bool  default: false
  309.   --expose-wasm (expose wasm interface to JavaScript)
  310.         type: bool  default: true
  311.   --assume-asmjs-origin (force wasm decoder to assume input is internal asm-wasm format)
  312.         type: bool  default: false
  313.   --wasm-num-compilation-tasks (maximum number of parallel compilation tasks for wasm)
  314.         type: int  default: 128
  315.   --wasm-write-protect-code-memory (write protect code memory on the wasm native heap)
  316.         type: bool  default: false
  317.   --wasm-async-compilation (enable actual asynchronous compilation for WebAssembly.compile)
  318.         type: bool  default: true
  319.   --wasm-test-streaming (use streaming compilation instead of async compilation for tests)
  320.         type: bool  default: false
  321.   --wasm-max-mem-pages (maximum initial number of 64KiB memory pages of a wasm instance)
  322.         type: uint  default: 32767
  323.   --wasm-max-mem-pages-growth (maximum number of 64KiB pages a Wasm memory can grow to)
  324.         type: uint  default: 65536
  325.   --wasm-max-table-size (maximum table size of a wasm instance)
  326.         type: uint  default: 10000000
  327.   --wasm-max-code-space (maximum committed code space for wasm (in MB))
  328.         type: uint  default: 1024
  329.   --wasm-tier-up (enable tier up to the optimizing compiler (requires --liftoff to have an effect))
  330.         type: bool  default: true
  331.   --trace-wasm-ast-start (start function for wasm AST trace (inclusive))
  332.         type: int  default: 0
  333.   --trace-wasm-ast-end (end function for wasm AST trace (exclusive))
  334.         type: int  default: 0
  335.   --liftoff (enable Liftoff, the baseline compiler for WebAssembly)
  336.         type: bool  default: true
  337.   --trace-wasm-memory (print all memory updates performed in wasm code)
  338.         type: bool  default: false
  339.   --wasm-tier-mask-for-testing (bitmask of functions to compile with TurboFan instead of Liftoff)
  340.         type: int  default: 0
  341.   --wasm-expose-debug-eval (Expose wasm evaluator support on the CDP)
  342.         type: bool  default: false
  343.   --validate-asm (validate asm.js modules before compiling)
  344.         type: bool  default: true
  345.   --suppress-asm-messages (don't emit asm.js related messages (for golden file testing))
  346.         type: bool  default: false
  347.   --trace-asm-time (log asm.js timing info to the console)
  348.         type: bool  default: false
  349.   --trace-asm-scanner (log tokens encountered by asm.js scanner)
  350.         type: bool  default: false
  351.   --trace-asm-parser (verbose logging of asm.js parse failures)
  352.         type: bool  default: false
  353.   --stress-validate-asm (try to validate everything as asm.js)
  354.         type: bool  default: false
  355.   --dump-wasm-module-path (directory to dump wasm modules to)
  356.         type: string  default: nullptr
  357.   --experimental-wasm-eh (enable prototype exception handling opcodes for wasm)
  358.         type: bool  default: false
  359.   --experimental-wasm-simd (enable prototype SIMD opcodes for wasm)
  360.         type: bool  default: false
  361.   --experimental-wasm-return-call (enable prototype return call opcodes for wasm)
  362.         type: bool  default: false
  363.   --experimental-wasm-compilation-hints (enable prototype compilation hints section for wasm)
  364.         type: bool  default: false
  365.   --experimental-wasm-gc (enable prototype garbage collection for wasm)
  366.         type: bool  default: false
  367.   --experimental-wasm-typed-funcref (enable prototype typed function references for wasm)
  368.         type: bool  default: false
  369.   --experimental-wasm-reftypes (enable prototype reference type opcodes for wasm)
  370.         type: bool  default: false
  371.   --experimental-wasm-threads (enable prototype thread opcodes for wasm)
  372.         type: bool  default: false
  373.   --experimental-wasm-type-reflection (enable prototype wasm type reflection in JS for wasm)
  374.         type: bool  default: false
  375.   --experimental-wasm-bigint (enable prototype JS BigInt support for wasm)
  376.         type: bool  default: true
  377.   --experimental-wasm-bulk-memory (enable prototype bulk memory opcodes for wasm)
  378.         type: bool  default: true
  379.   --experimental-wasm-mv (enable prototype multi-value support for wasm)
  380.         type: bool  default: true
  381.   --wasm-staging (enable staged wasm features)
  382.         type: bool  default: false
  383.   --wasm-opt (enable wasm optimization)
  384.         type: bool  default: false
  385.   --wasm-bounds-checks (enable bounds checks (disable for performance testing only))
  386.         type: bool  default: true
  387.   --wasm-stack-checks (enable stack checks (disable for performance testing only))
  388.         type: bool  default: true
  389.   --wasm-math-intrinsics (intrinsify some Math imports into wasm)
  390.         type: bool  default: true
  391.   --wasm-trap-handler (use signal handlers to catch out of bounds memory access in wasm (currently Linux x86_64 only))
  392.         type: bool  default: true
  393.   --wasm-fuzzer-gen-test (generate a test case when running a wasm fuzzer)
  394.         type: bool  default: false
  395.   --print-wasm-code (Print WebAssembly code)
  396.         type: bool  default: false
  397.   --print-wasm-stub-code (Print WebAssembly stub code)
  398.         type: bool  default: false
  399.   --asm-wasm-lazy-compilation (enable lazy compilation for asm-wasm modules)
  400.         type: bool  default: false
  401.   --wasm-lazy-compilation (enable lazy compilation for all wasm modules)
  402.         type: bool  default: false
  403.   --wasm-lazy-validation (enable lazy validation for lazily compiled wasm functions)
  404.         type: bool  default: false
  405.   --wasm-atomics-on-non-shared-memory (allow atomic operations on non-shared WebAssembly memory)
  406.         type: bool  default: true
  407.   --wasm-grow-shared-memory (allow growing shared WebAssembly memory objects)
  408.         type: bool  default: true
  409.   --wasm-simd-post-mvp (allow experimental SIMD operations for prototyping that are not included in the current proposal)
  410.         type: bool  default: false
  411.   --wasm-code-gc (enable garbage collection of wasm code)
  412.         type: bool  default: true
  413.   --trace-wasm-code-gc (trace garbage collection of wasm code)
  414.         type: bool  default: false
  415.   --stress-wasm-code-gc (stress test garbage collection of wasm code)
  416.         type: bool  default: false
  417.   --wasm-max-initial-code-space-reservation (maximum size of the initial wasm code space reservation (in MB))
  418.         type: int  default: 0
  419.   --frame-count (number of stack frames inspected by the profiler)
  420.         type: int  default: 1
  421.   --stress-sampling-allocation-profiler (Enables sampling allocation profiler with X as a sample interval)
  422.         type: int  default: 0
  423.   --lazy-new-space-shrinking (Enables the lazy new space shrinking strategy)
  424.         type: bool  default: false
  425.   --min-semi-space-size (min size of a semi-space (in MBytes), the new space consists of two semi-spaces)
  426.         type: size_t  default: 0
  427.   --max-semi-space-size (max size of a semi-space (in MBytes), the new space consists of two semi-spaces)
  428.         type: size_t  default: 0
  429.   --semi-space-growth-factor (factor by which to grow the new space)
  430.         type: int  default: 2
  431.   --max-old-space-size (max size of the old space (in Mbytes))
  432.         type: size_t  default: 0
  433.   --max-heap-size (max size of the heap (in Mbytes) both max_semi_space_size and max_old_space_size take precedence. All three flags cannot be specified at the same time.)
  434.         type: size_t  default: 0
  435.   --initial-heap-size (initial size of the heap (in Mbytes))
  436.         type: size_t  default: 0
  437.   --huge-max-old-generation-size (Increase max size of the old space to 4 GB for x64 systems withthe physical memory bigger than 16 GB)
  438.         type: bool  default: true
  439.   --initial-old-space-size (initial old space size (in Mbytes))
  440.         type: size_t  default: 0
  441.   --global-gc-scheduling (enable GC scheduling based on global memory)
  442.         type: bool  default: true
  443.   --gc-global (always perform global GCs)
  444.         type: bool  default: false
  445.   --random-gc-interval (Collect garbage after random(0, X) allocations. It overrides gc_interval.)
  446.         type: int  default: 0
  447.   --gc-interval (garbage collect after <n> allocations)
  448.         type: int  default: -1
  449.   --retain-maps-for-n-gc (keeps maps alive for <n> old space garbage collections)
  450.         type: int  default: 2
  451.   --trace-gc (print one trace line following each garbage collection)
  452.         type: bool  default: false
  453.   --trace-gc-nvp (print one detailed trace line in name=value format after each garbage collection)
  454.         type: bool  default: false
  455.   --trace-gc-ignore-scavenger (do not print trace line after scavenger collection)
  456.         type: bool  default: false
  457.   --trace-idle-notification (print one trace line following each idle notification)
  458.         type: bool  default: false
  459.   --trace-idle-notification-verbose (prints the heap state used by the idle notification)
  460.         type: bool  default: false
  461.   --trace-gc-verbose (print more details following each garbage collection)
  462.         type: bool  default: false
  463.   --trace-gc-freelists (prints details of each freelist before and after each major garbage collection)
  464.         type: bool  default: false
  465.   --trace-gc-freelists-verbose (prints details of freelists of each page before and after each major garbage collection)
  466.         type: bool  default: false
  467.   --trace-evacuation-candidates (Show statistics about the pages evacuation by the compaction)
  468.         type: bool  default: false
  469.   --trace-allocations-origins (Show statistics about the origins of allocations. Combine with --no-inline-new to track allocations from generated code)
  470.         type: bool  default: false
  471.   --trace-allocation-stack-interval (print stack trace after <n> free-list allocations)
  472.         type: int  default: -1
  473.   --trace-duplicate-threshold-kb (print duplicate objects in the heap if their size is more than given threshold)
  474.         type: int  default: 0
  475.   --trace-fragmentation (report fragmentation for old space)
  476.         type: bool  default: false
  477.   --trace-fragmentation-verbose (report fragmentation for old space (detailed))
  478.         type: bool  default: false
  479.   --minor-mc-trace-fragmentation (trace fragmentation after marking)
  480.         type: bool  default: false
  481.   --trace-evacuation (report evacuation statistics)
  482.         type: bool  default: false
  483.   --trace-mutator-utilization (print mutator utilization, allocation speed, gc speed)
  484.         type: bool  default: false
  485.   --incremental-marking (use incremental marking)
  486.         type: bool  default: true
  487.   --incremental-marking-wrappers (use incremental marking for marking wrappers)
  488.         type: bool  default: true
  489.   --incremental-marking-task (use tasks for incremental marking)
  490.         type: bool  default: true
  491.   --incremental-marking-soft-trigger (threshold for starting incremental marking via a task in percent of available space: limit - size)
  492.         type: int  default: 0
  493.   --incremental-marking-hard-trigger (threshold for starting incremental marking immediately in percent of available space: limit - size)
  494.         type: int  default: 0
  495.   --trace-unmapper (Trace the unmapping)
  496.         type: bool  default: false
  497.   --parallel-scavenge (parallel scavenge)
  498.         type: bool  default: true
  499.   --scavenge-task (schedule scavenge tasks)
  500.         type: bool  default: true
  501.   --scavenge-task-trigger (scavenge task trigger in percent of the current heap limit)
  502.         type: int  default: 80
  503.   --scavenge-separate-stack-scanning (use a separate phase for stack scanning in scavenge)
  504.         type: bool  default: false
  505.   --trace-parallel-scavenge (trace parallel scavenge)
  506.         type: bool  default: false
  507.   --write-protect-code-memory (write protect code memory)
  508.         type: bool  default: true
  509.   --concurrent-marking (use concurrent marking)
  510.         type: bool  default: true
  511.   --concurrent-array-buffer-sweeping (concurrently sweep array buffers)
  512.         type: bool  default: true
  513.   --concurrent-allocation (concurrently allocate in old space)
  514.         type: bool  default: false
  515.   --local-heaps (allow heap access from background tasks)
  516.         type: bool  default: false
  517.   --stress-concurrent-allocation (start background threads that allocate memory)
  518.         type: bool  default: false
  519.   --parallel-marking (use parallel marking in atomic pause)
  520.         type: bool  default: true
  521.   --ephemeron-fixpoint-iterations (number of fixpoint iterations it takes to switch to linear ephemeron algorithm)
  522.         type: int  default: 10
  523.   --trace-concurrent-marking (trace concurrent marking)
  524.         type: bool  default: false
  525.   --concurrent-store-buffer (use concurrent store buffer processing)
  526.         type: bool  default: true
  527.   --concurrent-sweeping (use concurrent sweeping)
  528.         type: bool  default: true
  529.   --parallel-compaction (use parallel compaction)
  530.         type: bool  default: true
  531.   --parallel-pointer-update (use parallel pointer update during compaction)
  532.         type: bool  default: true
  533.   --detect-ineffective-gcs-near-heap-limit (trigger out-of-memory failure to avoid GC storm near heap limit)
  534.         type: bool  default: true
  535.   --trace-incremental-marking (trace progress of the incremental marking)
  536.         type: bool  default: false
  537.   --trace-stress-marking (trace stress marking progress)
  538.         type: bool  default: false
  539.   --trace-stress-scavenge (trace stress scavenge progress)
  540.         type: bool  default: false
  541.   --track-gc-object-stats (track object counts and memory usage)
  542.         type: bool  default: false
  543.   --trace-gc-object-stats (trace object counts and memory usage)
  544.         type: bool  default: false
  545.   --trace-zone-stats (trace zone memory usage)
  546.         type: bool  default: false
  547.   --zone-stats-tolerance (report a tick only when allocated zone memory changes by this amount)
  548.         type: size_t  default: 1048576
  549.   --track-retaining-path (enable support for tracking retaining path)
  550.         type: bool  default: false
  551.   --concurrent-array-buffer-freeing (free array buffer allocations on a background thread)
  552.         type: bool  default: true
  553.   --gc-stats (Used by tracing internally to enable gc statistics)
  554.         type: int  default: 0
  555.   --track-detached-contexts (track native contexts that are expected to be garbage collected)
  556.         type: bool  default: true
  557.   --trace-detached-contexts (trace native contexts that are expected to be garbage collected)
  558.         type: bool  default: false
  559.   --move-object-start (enable moving of object starts)
  560.         type: bool  default: true
  561.   --memory-reducer (use memory reducer)
  562.         type: bool  default: true
  563.   --memory-reducer-for-small-heaps (use memory reducer for small heaps)
  564.         type: bool  default: true
  565.   --heap-growing-percent (specifies heap growing factor as (1 + heap_growing_percent/100))
  566.         type: int  default: 0
  567.   --v8-os-page-size (override OS page size (in KBytes))
  568.         type: int  default: 0
  569.   --always-compact (Perform compaction on every full GC)
  570.         type: bool  default: false
  571.   --never-compact (Never perform compaction on full GC - testing only)
  572.         type: bool  default: false
  573.   --compact-code-space (Compact code space on full collections)
  574.         type: bool  default: true
  575.   --flush-bytecode (flush of bytecode when it has not been executed recently)
  576.         type: bool  default: true
  577.   --stress-flush-bytecode (stress bytecode flushing)
  578.         type: bool  default: false
  579.   --use-marking-progress-bar (Use a progress bar to scan large objects in increments when incremental marking is active.)
  580.         type: bool  default: true
  581.   --stress-per-context-marking-worklist (Use per-context worklist for marking)
  582.         type: bool  default: false
  583.   --force-marking-deque-overflows (force overflows of marking deque by reducing it's size to 64 words)
  584.         type: bool  default: false
  585.   --stress-compaction (stress the GC compactor to flush out bugs (implies --force_marking_deque_overflows))
  586.         type: bool  default: false
  587.   --stress-compaction-random (Stress GC compaction by selecting random percent of pages as evacuation candidates. It overrides stress_compaction.)
  588.         type: bool  default: false
  589.   --stress-incremental-marking (force incremental marking for small heaps and run it more often)
  590.         type: bool  default: false
  591.   --fuzzer-gc-analysis (prints number of allocations and enables analysis mode for gc fuzz testing, e.g. --stress-marking, --stress-scavenge)
  592.         type: bool  default: false
  593.   --stress-marking (force marking at random points between 0 and X (inclusive) percent of the regular marking start limit)
  594.         type: int  default: 0
  595.   --stress-scavenge (force scavenge at random points between 0 and X (inclusive) percent of the new space capacity)
  596.         type: int  default: 0
  597.   --gc-experiment-background-schedule (new background GC schedule heuristics)
  598.         type: bool  default: false
  599.   --gc-experiment-less-compaction (less compaction in non-memory reducing mode)
  600.         type: bool  default: false
  601.   --disable-abortjs (disables AbortJS runtime function)
  602.         type: bool  default: false
  603.   --randomize-all-allocations (randomize virtual memory reservations by ignoring any hints passed when allocating pages)
  604.         type: bool  default: false
  605.   --manual-evacuation-candidates-selection (Test mode only flag. It allows an unit test to select evacuation candidates pages (requires --stress_compaction).)
  606.         type: bool  default: false
  607.   --fast-promotion-new-space (fast promote new space on high survival rates)
  608.         type: bool  default: false
  609.   --clear-free-memory (initialize free memory with 0)
  610.         type: bool  default: false
  611.   --young-generation-large-objects (allocates large objects by default in the young generation large object space)
  612.         type: bool  default: true
  613.   --debug-code (generate extra code (assertions) for debugging)
  614.         type: bool  default: false
  615.   --code-comments (emit comments in code disassembly; for more readable source positions you should add --no-concurrent_recompilation)
  616.         type: bool  default: false
  617.   --enable-sse3 (enable use of SSE3 instructions if available)
  618.         type: bool  default: true
  619.   --enable-ssse3 (enable use of SSSE3 instructions if available)
  620.         type: bool  default: true
  621.   --enable-sse4-1 (enable use of SSE4.1 instructions if available)
  622.         type: bool  default: true
  623.   --enable-sse4-2 (enable use of SSE4.2 instructions if available)
  624.         type: bool  default: true
  625.   --enable-sahf (enable use of SAHF instruction if available (X64 only))
  626.         type: bool  default: true
  627.   --enable-avx (enable use of AVX instructions if available)
  628.         type: bool  default: true
  629.   --enable-fma3 (enable use of FMA3 instructions if available)
  630.         type: bool  default: true
  631.   --enable-bmi1 (enable use of BMI1 instructions if available)
  632.         type: bool  default: true
  633.   --enable-bmi2 (enable use of BMI2 instructions if available)
  634.         type: bool  default: true
  635.   --enable-lzcnt (enable use of LZCNT instruction if available)
  636.         type: bool  default: true
  637.   --enable-popcnt (enable use of POPCNT instruction if available)
  638.         type: bool  default: true
  639.   --arm-arch (generate instructions for the selected ARM architecture if available: armv6, armv7, armv7+sudiv or armv8)
  640.         type: string  default: armv8
  641.   --force-long-branches (force all emitted branches to be in long mode (MIPS/PPC only))
  642.         type: bool  default: false
  643.   --mcpu (enable optimization for specific cpu)
  644.         type: string  default: auto
  645.   --partial-constant-pool (enable use of partial constant pools (X64 only))
  646.         type: bool  default: true
  647.   --sim-arm64-optional-features (enable optional features on the simulator for testing: none or all)
  648.         type: string  default: none
  649.   --enable-source-at-csa-bind (Include source information in the binary at CSA bind locations.)
  650.         type: bool  default: false
  651.   --enable-armv7 (deprecated (use --arm_arch instead))
  652.         type: maybe_bool  default: unset
  653.   --enable-vfp3 (deprecated (use --arm_arch instead))
  654.         type: maybe_bool  default: unset
  655.   --enable-32dregs (deprecated (use --arm_arch instead))
  656.         type: maybe_bool  default: unset
  657.   --enable-neon (deprecated (use --arm_arch instead))
  658.         type: maybe_bool  default: unset
  659.   --enable-sudiv (deprecated (use --arm_arch instead))
  660.         type: maybe_bool  default: unset
  661.   --enable-armv8 (deprecated (use --arm_arch instead))
  662.         type: maybe_bool  default: unset
  663.   --enable-regexp-unaligned-accesses (enable unaligned accesses for the regexp engine)
  664.         type: bool  default: true
  665.   --script-streaming (enable parsing on background)
  666.         type: bool  default: true
  667.   --stress-background-compile (stress test parsing on background)
  668.         type: bool  default: false
  669.   --finalize-streaming-on-background (perform the script streaming finalization on the background thread)
  670.         type: bool  default: false
  671.   --disable-old-api-accessors (Disable old-style API accessors whose setters trigger through the prototype chain)
  672.         type: bool  default: false
  673.   --expose-gc (expose gc extension)
  674.         type: bool  default: false
  675.   --expose-gc-as (expose gc extension under the specified name)
  676.         type: string  default: nullptr
  677.   --expose-externalize-string (expose externalize string extension)
  678.         type: bool  default: false
  679.   --expose-trigger-failure (expose trigger-failure extension)
  680.         type: bool  default: false
  681.   --stack-trace-limit (number of stack frames to capture)
  682.         type: int  default: 10
  683.   --builtins-in-stack-traces (show built-in functions in stack traces)
  684.         type: bool  default: false
  685.   --experimental-stack-trace-frames (enable experimental frames (API/Builtins) and stack trace layout)
  686.         type: bool  default: false
  687.   --disallow-code-generation-from-strings (disallow eval and friends)
  688.         type: bool  default: false
  689.   --expose-async-hooks (expose async_hooks object)
  690.         type: bool  default: false
  691.   --expose-cputracemark-as (expose cputracemark extension under the specified name)
  692.         type: string  default: nullptr
  693.   --allow-unsafe-function-constructor (allow invoking the function constructor without security checks)
  694.         type: bool  default: false
  695.   --force-slow-path (always take the slow path for builtins)
  696.         type: bool  default: false
  697.   --test-small-max-function-context-stub-size (enable testing the function context size overflow path by making the maximum size smaller)
  698.         type: bool  default: false
  699.   --inline-new (use fast inline allocation)
  700.         type: bool  default: true
  701.   --trace (trace javascript function calls)
  702.         type: bool  default: false
  703.   --trace-wasm (trace wasm function calls)
  704.         type: bool  default: false
  705.   --lazy (use lazy compilation)
  706.         type: bool  default: true
  707.   --max-lazy (ignore eager compilation hints)
  708.         type: bool  default: false
  709.   --trace-opt (trace lazy optimization)
  710.         type: bool  default: false
  711.   --trace-opt-verbose (extra verbose compilation tracing)
  712.         type: bool  default: false
  713.   --trace-opt-stats (trace lazy optimization statistics)
  714.         type: bool  default: false
  715.   --trace-deopt (trace optimize function deoptimization)
  716.         type: bool  default: false
  717.   --trace-file-names (include file names in trace-opt/trace-deopt output)
  718.         type: bool  default: false
  719.   --always-opt (always try to optimize functions)
  720.         type: bool  default: false
  721.   --always-osr (always try to OSR functions)
  722.         type: bool  default: false
  723.   --prepare-always-opt (prepare for turning on always opt)
  724.         type: bool  default: false
  725.   --trace-serializer (print code serializer trace)
  726.         type: bool  default: false
  727.   --compilation-cache (enable compilation cache)
  728.         type: bool  default: true
  729.   --cache-prototype-transitions (cache prototype transitions)
  730.         type: bool  default: true
  731.   --parallel-compile-tasks (enable parallel compile tasks)
  732.         type: bool  default: false
  733.   --compiler-dispatcher (enable compiler dispatcher)
  734.         type: bool  default: false
  735.   --trace-compiler-dispatcher (trace compiler dispatcher activity)
  736.         type: bool  default: false
  737.   --cpu-profiler-sampling-interval (CPU profiler sampling interval in microseconds)
  738.         type: int  default: 1000
  739.   --trace-side-effect-free-debug-evaluate (print debug messages for side-effect-free debug-evaluate for testing)
  740.         type: bool  default: false
  741.   --hard-abort (abort by crashing)
  742.         type: bool  default: true
  743.   --expose-inspector-scripts (expose injected-script-source.js for debugging)
  744.         type: bool  default: false
  745.   --stack-size (default size of stack region v8 is allowed to use (in kBytes))
  746.         type: int  default: 984
  747.   --max-stack-trace-source-length (maximum length of function source code printed in a stack trace.)
  748.         type: int  default: 300
  749.   --clear-exceptions-on-js-entry (clear pending exceptions when entering JavaScript)
  750.         type: bool  default: false
  751.   --histogram-interval (time interval in ms for aggregating memory histograms)
  752.         type: int  default: 600000
  753.   --heap-profiler-trace-objects (Dump heap object allocations/movements/size_updates)
  754.         type: bool  default: false
  755.   --heap-profiler-use-embedder-graph (Use the new EmbedderGraph API to get embedder nodes)
  756.         type: bool  default: true
  757.   --heap-snapshot-string-limit (truncate strings to this length in the heap snapshot)
  758.         type: int  default: 1024
  759.   --sampling-heap-profiler-suppress-randomness (Use constant sample intervals to eliminate test flakiness)
  760.         type: bool  default: false
  761.   --use-idle-notification (Use idle notification to reduce memory footprint.)
  762.         type: bool  default: true
  763.   --trace-ic (trace inline cache state transitions for tools/ic-processor)
  764.         type: bool  default: false
  765.   --modify-field-representation-inplace (enable in-place field representation updates)
  766.         type: bool  default: true
  767.   --max-polymorphic-map-count (maximum number of maps to track in POLYMORPHIC state)
  768.         type: int  default: 4
  769.   --native-code-counters (generate extra code for manipulating stats counters)
  770.         type: bool  default: false
  771.   --thin-strings (Enable ThinString support)
  772.         type: bool  default: true
  773.   --trace-prototype-users (Trace updates to prototype user tracking)
  774.         type: bool  default: false
  775.   --trace-for-in-enumerate (Trace for-in enumerate slow-paths)
  776.         type: bool  default: false
  777.   --trace-maps (trace map creation)
  778.         type: bool  default: false
  779.   --trace-maps-details (also log map details)
  780.         type: bool  default: true
  781.   --allow-natives-syntax (allow natives syntax)
  782.         type: bool  default: false
  783.   --allow-natives-for-differential-fuzzing (allow only natives explicitly allowlisted for differential fuzzers)
  784.         type: bool  default: false
  785.   --parse-only (only parse the sources)
  786.         type: bool  default: false
  787.   --trace-sim (Trace simulator execution)
  788.         type: bool  default: false
  789.   --debug-sim (Enable debugging the simulator)
  790.         type: bool  default: false
  791.   --check-icache (Check icache flushes in ARM and MIPS simulator)
  792.         type: bool  default: false
  793.   --stop-sim-at (Simulator stop after x number of instructions)
  794.         type: int  default: 0
  795.   --sim-stack-alignment (Stack alingment in bytes in simulator (4 or 8, 8 is default))
  796.         type: int  default: 8
  797.   --sim-stack-size (Stack size of the ARM64, MIPS64 and PPC64 simulator in kBytes (default is 2 MB))
  798.         type: int  default: 2048
  799.   --log-colour (When logging, try to use coloured output.)
  800.         type: bool  default: true
  801.   --trace-sim-messages (Trace simulator debug messages. Implied by --trace-sim.)
  802.         type: bool  default: false
  803.   --async-stack-traces (include async stack traces in Error.stack)
  804.         type: bool  default: true
  805.   --stack-trace-on-illegal (print stack trace when an illegal exception is thrown)
  806.         type: bool  default: false
  807.   --abort-on-uncaught-exception (abort program (dump core) when an uncaught exception is thrown)
  808.         type: bool  default: false
  809.   --correctness-fuzzer-suppressions (Suppress certain unspecified behaviors to ease correctness fuzzing: Abort program when the stack overflows or a string exceeds maximum length (as opposed to throwing RangeError). Use a fixed suppression string for error messages.)
  810.         type: bool  default: false
  811.   --randomize-hashes (randomize hashes to avoid predictable hash collisions (with snapshots this option cannot override the baked-in seed))
  812.         type: bool  default: true
  813.   --rehash-snapshot (rehash strings from the snapshot to override the baked-in seed)
  814.         type: bool  default: true
  815.   --hash-seed (Fixed seed to use to hash property keys (0 means random)(with snapshots this option cannot override the baked-in seed))
  816.         type: uint64  default: 0
  817.   --random-seed (Default seed for initializing random generator (0, the default, means to use system random).)
  818.         type: int  default: 0
  819.   --fuzzer-random-seed (Default seed for initializing fuzzer random generator (0, the default, means to use v8's random number generator seed).)
  820.         type: int  default: 0
  821.   --trace-rail (trace RAIL mode)
  822.         type: bool  default: false
  823.   --print-all-exceptions (print exception object and stack trace on each thrown exception)
  824.         type: bool  default: false
  825.   --detailed-error-stack-trace (includes arguments for each function call in the error stack frames array)
  826.         type: bool  default: false
  827.   --adjust-os-scheduling-parameters (adjust OS specific scheduling params for the isolate)
  828.         type: bool  default: true
  829.   --runtime-call-stats (report runtime call counts and times)
  830.         type: bool  default: false
  831.   --rcs (report runtime call counts and times)
  832.         type: bool  default: false
  833.   --rcs-cpu-time (report runtime times in cpu time (the default is wall time))
  834.         type: bool  default: false
  835.   --profile-deserialization (Print the time it takes to deserialize the snapshot.)
  836.         type: bool  default: false
  837.   --serialization-statistics (Collect statistics on serialized objects.)
  838.         type: bool  default: false
  839.   --serialization-chunk-size (Custom size for serialization chunks)
  840.         type: uint  default: 4096
  841.   --regexp-optimization (generate optimized regexp code)
  842.         type: bool  default: true
  843.   --regexp-mode-modifiers (enable inline flags in regexp.)
  844.         type: bool  default: false
  845.   --regexp-interpret-all (interpret all regexp code)
  846.         type: bool  default: false
  847.   --regexp-tier-up (enable regexp interpreter and tier up to the compiler after the number of executions set by the tier up ticks flag)
  848.         type: bool  default: true
  849.   --regexp-tier-up-ticks (set the number of executions for the regexp interpreter before tiering-up to the compiler)
  850.         type: int  default: 1
  851.   --regexp-peephole-optimization (enable peephole optimization for regexp bytecode)
  852.         type: bool  default: true
  853.   --trace-regexp-peephole-optimization (trace regexp bytecode peephole optimization)
  854.         type: bool  default: false
  855.   --trace-regexp-bytecodes (trace regexp bytecode execution)
  856.         type: bool  default: false
  857.   --trace-regexp-assembler (trace regexp macro assembler calls.)
  858.         type: bool  default: false
  859.   --trace-regexp-parser (trace regexp parsing)
  860.         type: bool  default: false
  861.   --trace-regexp-tier-up (trace regexp tiering up execution)
  862.         type: bool  default: false
  863.   --testing-bool-flag (testing_bool_flag)
  864.         type: bool  default: true
  865.   --testing-maybe-bool-flag (testing_maybe_bool_flag)
  866.         type: maybe_bool  default: unset
  867.   --testing-int-flag (testing_int_flag)
  868.         type: int  default: 13
  869.   --testing-float-flag (float-flag)
  870.         type: float  default: 2.5
  871.   --testing-string-flag (string-flag)
  872.         type: string  default: Hello, world!
  873.   --testing-prng-seed (Seed used for threading test randomness)
  874.         type: int  default: 42
  875.   --testing-d8-test-runner (test runner turns on this flag to enable a check that the function was prepared for optimization before marking it for optimization)
  876.         type: bool  default: false
  877.   --fuzzing (Fuzzers use this flag to signal that they are ... fuzzing. This causes intrinsics to fail silently (e.g. return undefined) on invalid usage.)
  878.         type: bool  default: false
  879.   --embedded-src (Path for the generated embedded data file. (mksnapshot only))
  880.         type: string  default: nullptr
  881.   --embedded-variant (Label to disambiguate symbols in embedded data file. (mksnapshot only))
  882.         type: string  default: nullptr
  883.   --startup-src (Write V8 startup as C++ src. (mksnapshot only))
  884.         type: string  default: nullptr
  885.   --startup-blob (Write V8 startup blob file. (mksnapshot only))
  886.         type: string  default: nullptr
  887.   --target-arch (The mksnapshot target arch. (mksnapshot only))
  888.         type: string  default: nullptr
  889.   --target-os (The mksnapshot target os. (mksnapshot only))
  890.         type: string  default: nullptr
  891.   --target-is-simulator (Instruct mksnapshot that the target is meant to run in the simulator and it can generate simulator-specific instructions. (mksnapshot only))
  892.         type: bool  default: false
  893.   --minor-mc-parallel-marking (use parallel marking for the young generation)
  894.         type: bool  default: true
  895.   --trace-minor-mc-parallel-marking (trace parallel marking for the young generation)
  896.         type: bool  default: false
  897.   --minor-mc (perform young generation mark compact GCs)
  898.         type: bool  default: false
  899.   --help (Print usage message, including flags, on console)
  900.         type: bool  default: true
  901.   --dump-counters (Dump counters on exit)
  902.         type: bool  default: false
  903.   --dump-counters-nvp (Dump counters as name-value pairs on exit)
  904.         type: bool  default: false
  905.   --use-external-strings (Use external strings for source code)
  906.         type: bool  default: false
  907.   --map-counters (Map counters to a file)
  908.         type: string  default:
  909.   --mock-arraybuffer-allocator (Use a mock ArrayBuffer allocator for testing.)
  910.         type: bool  default: false
  911.   --mock-arraybuffer-allocator-limit (Memory limit for mock ArrayBuffer allocator used to simulate OOM for testing.)
  912.         type: size_t  default: 0
  913.   --gdbjit (enable GDBJIT interface)
  914.         type: bool  default: false
  915.   --gdbjit-full (enable GDBJIT interface for all code objects)
  916.         type: bool  default: false
  917.   --gdbjit-dump (dump elf objects with debug info to disk)
  918.         type: bool  default: false
  919.   --gdbjit-dump-filter (dump only objects containing this substring)
  920.         type: string  default:
  921.   --log (Minimal logging (no API, code, GC, suspect, or handles samples).)
  922.         type: bool  default: false
  923.   --log-all (Log all events to the log file.)
  924.         type: bool  default: false
  925.   --log-api (Log API events to the log file.)
  926.         type: bool  default: false
  927.   --log-code (Log code events to the log file without profiling.)
  928.         type: bool  default: false
  929.   --log-handles (Log global handle events.)
  930.         type: bool  default: false
  931.   --log-suspect (Log suspect operations.)
  932.         type: bool  default: false
  933.   --log-source-code (Log source code.)
  934.         type: bool  default: false
  935.   --log-function-events (Log function events (parse, compile, execute) separately.)
  936.         type: bool  default: false
  937.   --prof (Log statistical profiling information (implies --log-code).)
  938.         type: bool  default: false
  939.   --detailed-line-info (Always generate detailed line information for CPU profiling.)
  940.         type: bool  default: false
  941.   --prof-sampling-interval (Interval for --prof samples (in microseconds).)
  942.         type: int  default: 1000
  943.   --prof-cpp (Like --prof, but ignore generated code.)
  944.         type: bool  default: false
  945.   --prof-browser-mode (Used with --prof, turns on browser-compatible mode for profiling.)
  946.         type: bool  default: true
  947.   --logfile (Specify the name of the log file.)
  948.         type: string  default: v8.log
  949.   --logfile-per-isolate (Separate log files for each isolate.)
  950.         type: bool  default: true
  951.   --ll-prof (Enable low-level linux profiler.)
  952.         type: bool  default: false
  953.   --gc-fake-mmap (Specify the name of the file for fake gc mmap used in ll_prof)
  954.         type: string  default: /tmp/__v8_gc__
  955.   --log-internal-timer-events (Time internal events.)
  956.         type: bool  default: false
  957.   --redirect-code-traces (output deopt information and disassembly into file code-<pid>-<isolate id>.asm)
  958.         type: bool  default: false
  959.   --redirect-code-traces-to (output deopt information and disassembly into the given file)
  960.         type: string  default: nullptr
  961.   --print-opt-source (print source code of optimized and inlined functions)
  962.         type: bool  default: false
  963.   --vtune-prof-annotate-wasm (Used when v8_enable_vtunejit is enabled, load wasm source map and provide annotate support (experimental).)
  964.         type: bool  default: false
  965.   --win64-unwinding-info (Enable unwinding info for Windows/x64)
  966.         type: bool  default: true
  967.   --interpreted-frames-native-stack (Show interpreted frames on the native stack (useful for external profilers).)
  968.         type: bool  default: false
  969.   --predictable (enable predictable mode)
  970.         type: bool  default: false
  971.   --predictable-gc-schedule (Predictable garbage collection schedule. Fixes heap growing, idle, and memory reducing behavior.)
  972.         type: bool  default: false
  973.   --single-threaded (disable the use of background tasks)
  974.         type: bool  default: false
  975.   --single-threaded-gc (disable the use of background gc tasks)
  976.         type: bool  default: false

Particularly useful ones:

  1. --async-stack-trace