Provided by: binaryen_120-4_amd64 
NAME
wasm-opt - Read, write, and optimize files
DESCRIPTION
================================================================================ wasm-opt INFILE
Read, write, and optimize files
================================================================================
wasm-opt options: -----------------
--output,-o
Output file (stdout if not specified)
--emit-text,-S
Emit text instead of binary for the output file
--converge,-c
Run passes to convergence, continuing while binary size decreases
--fuzz-exec-before,-feh
Execute functions before optimization, helping fuzzing find bugs
--fuzz-exec,-fe
Execute functions before and after optimization, helping fuzzing find bugs
--extra-fuzz-command,-efc
An extra command to run on the output before and after optimizing. The output is compared between
the two, and an error occurs if they are not equal
--translate-to-fuzz,-ttf
Translate the input into a valid wasm module *somehow*, useful for fuzzing
--initial-fuzz,-if
Initial wasm content in translate-to-fuzz (-ttf) mode
--fuzz-passes,-fp
Pick a random set of passes to run, useful for fuzzing. this depends on translate-to-fuzz (it
picks the passes from the input)
--no-fuzz-memory
don't emit memory ops when fuzzing
--no-fuzz-oob
don't emit out-of-bounds loads/stores/indirect calls when fuzzing
--emit-spec-wrapper,-esw
Emit a wasm spec interpreter wrapper file that can run the wasm with some test values, useful for
fuzzing
--emit-wasm2c-wrapper,-esw
Emit a C wrapper file that can run the wasm after it is compiled with wasm2c, useful for fuzzing
--input-source-map,-ism
Consume source map from the specified file
--output-source-map,-osm
Emit source map to the specified file
--output-source-map-url,-osu
Emit specified string as source map URL
--experimental-new-eh
Deprecated; same as --emit-exnref
--emit-exnref
After running all requested transformations / optimizations, translate the instruction to use the
new EH instructions at the end. Depending on the optimization level specified, this may do some
more post-translation optimizations.
Optimization passes: --------------------
--abstract-type-refining
refine and merge abstract (never-created) types
--alignment-lowering
lower unaligned loads and stores to smaller aligned ones
--asyncify
async/await style transform, allowing pausing and resuming
--avoid-reinterprets
Tries to avoid reinterpret operations via more loads
--cfp propagate constant struct field values
--cfp-reftest
propagate constant struct field values, using ref.test
--coalesce-locals
reduce # of locals by coalescing
--coalesce-locals-learning
reduce # of locals by coalescing and learning
--code-folding
fold code, merging duplicates
--code-pushing
push code forward, potentially making it not always execute
--const-hoisting
hoist repeated constants to a local
--dae removes arguments to calls in an lto-like manner
--dae-optimizing
removes arguments to calls in an lto-like manner, and optimizes where we removed
--dce removes unreachable code
--dealign
forces all loads and stores to have alignment 1
--denan
instrument the wasm to convert NaNs into 0 at runtime
--dfo optimizes using the DataFlow SSA IR
--directize
turns indirect calls into direct ones
--discard-global-effects
discards global effect info
--duplicate-function-elimination
removes duplicate functions
--duplicate-import-elimination
removes duplicate imports
--dwarfdump
dump DWARF debug info sections from the read binary
--emit-target-features
emit the target features section in the output
--extract-function
leaves just one function (useful for debugging)
--extract-function-index
leaves just one function selected by index
--flatten
flattens out code, removing nesting
--fpcast-emu
emulates function pointer casts, allowing incorrect indirect calls to (sometimes) work
--func-metrics
reports function metrics
--generate-dyncalls
generate dynCall fuctions used by emscripten ABI
--generate-global-effects
generate global effect info (helps later passes)
--generate-i64-dyncalls
generate dynCall functions used by emscripten ABI, but only for functions with i64 in their
signature (which cannot be invoked via the wasm table without JavaScript BigInt support).
--global-refining
refine the types of globals
--gsi globally optimize struct values
--gto globally optimize GC types
--gufa Grand Unified Flow Analysis: optimize the entire program using information about what content can
actually appear in each location
--gufa-cast-all
GUFA plus add casts for all inferences
--gufa-optimizing
GUFA plus local optimizations in functions we modified
--heap-store-optimization
optimize heap (GC) stores
--heap2local
replace GC allocations with locals
--i64-to-i32-lowering
lower all uses of i64s to use i32s instead
--inline-main
inline __original_main into main
--inlining
inline functions (you probably want inlining-optimizing)
--inlining-optimizing
inline functions and optimizes where we inlined
--instrument-locals
instrument the build with code to intercept all loads and stores
--instrument-memory
instrument the build with code to intercept all loads and stores
--intrinsic-lowering
lower away binaryen intrinsics
--jspi wrap imports and exports for JavaScript promise integration
--legalize-and-prune-js-interface
legalizes the import/export boundary and prunes when needed
--legalize-js-interface
legalizes i64 types on the import/export boundary
--licm loop invariant code motion
--limit-segments
attempt to merge segments to fit within web limits
--local-cse
common subexpression elimination inside basic blocks
--local-subtyping
apply more specific subtypes to locals where possible
--log-execution
instrument the build with logging of where execution goes
--memory-packing
packs memory into separate segments, skipping zeros
--memory64-lowering
lower loads and stores to a 64-bit memory to instead use a 32-bit one
--merge-blocks
merges blocks to their parents
--merge-j2cl-itables
Merges itable structures into vtables to make types more compact
--merge-locals
merges locals when beneficial
--merge-similar-functions
merges similar functions when benefical
--metrics
reports metrics (with an optional title, --metrics[=TITLE])
--minify-imports
minifies import names (only those, and not export names), and emits a mapping to the minified ones
--minify-imports-and-exports
minifies both import and export names, and emits a mapping to the minified ones
--minify-imports-and-exports-and-modules
minifies both import and export names, and emits a mapping to the minified ones, and minifies the
modules as well
--minimize-rec-groups
Split types into minimal recursion groups
--mod-asyncify-always-and-only-unwind
apply the assumption that asyncify imports always unwind, and we never rewind
--mod-asyncify-never-unwind
apply the assumption that asyncify never unwinds
--monomorphize
creates specialized versions of functions
--monomorphize-always
creates specialized versions of functions (even if unhelpful)
--multi-memory-lowering
combines multiple memories into a single memory
--multi-memory-lowering-with-bounds-checks
combines multiple memories into a single memory, trapping if the read or write is larger than the
length of the memory's data
--name-types
(re)name all heap types
--nm name list
--no-full-inline
mark functions as no-inline (for full inlining only)
--no-inline
mark functions as no-inline
--no-partial-inline
mark functions as no-inline (for partial inlining only)
--once-reduction
reduces calls to code that only runs once
--optimize-added-constants
optimizes added constants into load/store offsets
--optimize-added-constants-propagate
optimizes added constants into load/store offsets, propagating them across locals too
--optimize-casts
eliminate and reuse casts
--optimize-for-js
early optimize of the instruction combinations for js
--optimize-instructions
optimizes instruction combinations
--optimize-j2cl
optimizes J2CL specific constructs.
--outlining
outline instructions
--pick-load-signs
pick load signs based on their uses
--poppify
Tranform Binaryen IR into Poppy IR
--post-emscripten
miscellaneous optimizations for Emscripten-generated code
--precompute
computes compile-time evaluatable expressions
--precompute-propagate
computes compile-time evaluatable expressions and propagates them through locals
--print
print in s-expression format
--print-call-graph
print call graph
--print-features
print options for enabled features
--print-full
print in full s-expression format
--print-function-map
print a map of function indexes to names
--print-minified
print in minified s-expression format
--propagate-debug-locs
propagate debug location from parents or previous siblings to child nodes
--propagate-globals-globally
propagate global values to other globals (useful for tests)
--remove-imports
removes imports and replaces them with nops
--remove-memory
removes memory segments
--remove-non-js-ops
removes operations incompatible with js
--remove-unused-brs
removes breaks from locations that are not needed
--remove-unused-module-elements
removes unused module elements
--remove-unused-names
removes names from locations that are never branched to
--remove-unused-nonfunction-module-elements
removes unused module elements that are not functions
--remove-unused-types
remove unused private GC types
--reorder-functions
sorts functions by access frequency
--reorder-functions-by-name
sorts functions by name (useful for debugging)
--reorder-globals
sorts globals by access frequency
--reorder-locals
sorts locals by access frequency
--rereloop
re-optimize control flow using the relooper algorithm
--roundtrip
write the module to binary, then read it
--rse remove redundant local.sets
--safe-heap
instrument loads and stores to check for invalid behavior
--separate-data-segments
write data segments to a file and strip them from the module
--set-globals
sets specified globals to specified values
--signature-pruning
remove params from function signature types where possible
--signature-refining
apply more specific subtypes to signature types where possible
--signext-lowering
lower sign-ext operations to wasm mvp and disable the sign extension feature
--simplify-globals
miscellaneous globals-related optimizations
--simplify-globals-optimizing
miscellaneous globals-related optimizations, and optimizes where we replaced global.gets with
constants
--simplify-locals
miscellaneous locals-related optimizations
--simplify-locals-nonesting
miscellaneous locals-related optimizations (no nesting at all; preserves flatness)
--simplify-locals-nostructure
miscellaneous locals-related optimizations (no structure)
--simplify-locals-notee
miscellaneous locals-related optimizations (no tees)
--simplify-locals-notee-nostructure
miscellaneous locals-related optimizations (no tees or structure)
--souperify
emit Souper IR in text form
--souperify-single-use
emit Souper IR in text form (single-use nodes only)
--spill-pointers
spill pointers to the C stack (useful for Boehm-style GC)
--ssa ssa-ify variables so that they have a single assignment
--ssa-nomerge
ssa-ify variables so that they have a single assignment, ignoring merges
--stack-check
enforce limits on llvm's __stack_pointer global
--string-gathering
gathers wasm strings to globals
--string-lowering
lowers wasm strings and operations to imports
--string-lowering-magic-imports
same as string-lowering, but encodes well-formed strings as magic imports
--string-lowering-magic-imports-assert
same as string-lowering-magic-imports, but raise a fatal error if there are invalid strings
--strip
deprecated; same as strip-debug
--strip-debug
strip debug info (including the names section)
--strip-dwarf
strip dwarf debug info
--strip-eh
strip EH instructions
--strip-producers
strip the wasm producers section
--strip-target-features
strip the wasm target features section
--stub-unsupported-js
stub out unsupported JS operations
--symbolmap
(alias for print-function-map)
--table64-lowering
lower 64-bit tables 32-bit ones
--trace-calls
instrument the build with code to intercept specific function calls
--translate-to-exnref
translate old Phase 3 EH instructions to new ones with exnref
--translate-to-new-eh
deprecated; same as translate-to-exnref
--trap-mode-clamp
replace trapping operations with clamping semantics
--trap-mode-js
replace trapping operations with js semantics
--tuple-optimization
optimize trivial tuples away
--type-finalizing
mark all leaf types as final
--type-merging
merge types to their supertypes where possible
--type-refining
apply more specific subtypes to type fields where possible
--type-ssa
create new nominal types to help other optimizations
--type-unfinalizing
mark all types as non-final (open)
--unsubtyping
removes unnecessary subtyping relationships
--untee
removes local.tees, replacing them with sets and gets
--vacuum
removes obviously unneeded code
Optimization options: ---------------------
-O execute default optimization passes (equivalent to -Os)
-O0 execute no optimization passes
-O1 execute -O1 optimization passes (quick&useful opts, useful for iteration builds)
-O2 execute -O2 optimization passes (most opts, generally gets most perf)
-O3 execute -O3 optimization passes (spends potentially a lot of time optimizing)
-O4 execute -O4 optimization passes (also flatten the IR, which can take a lot more time and memory,
but is useful on more nested / complex / less-optimized input)
-Os execute default optimization passes, focusing on code size
-Oz execute default optimization passes, super-focusing on code size
--optimize-level,-ol
How much to focus on optimizing code
--shrink-level,-s
How much to focus on shrinking code size
--debuginfo,-g
Emit names section in wasm binary (or full debuginfo in wast)
--always-inline-max-function-size,-aimfs
Max size of functions that are always inlined (default 2, which is safe for use with -Os builds)
--flexible-inline-max-function-size,-fimfs
Max size of functions that are inlined when lightweight (no loops or function calls) when
optimizing aggressively for speed (-O3). Default: 20
--one-caller-inline-max-function-size,-ocimfs Max size of functions that are
inlined when there is only one caller (default -1, which means all such functions are inlined)
--inline-functions-with-loops,-ifwl
Allow inlining functions with loops
--partial-inlining-ifs,-pii
Number of ifs allowed in partial inlining (zero means partial inlining is disabled) (default: 0)
--ignore-implicit-traps,-iit
Optimize under the helpful assumption that no surprising traps occur (from load, div/mod, etc.)
--traps-never-happen,-tnh
Optimize under the helpful assumption that no trap is reached at runtime (from load, div/mod,
etc.)
--low-memory-unused,-lmu
Optimize under the helpful assumption that the low 1K of memory is not used by the application
--fast-math,-ffm
Optimize floats without handling corner cases of NaNs and rounding
--zero-filled-memory,-uim
Assume that an imported memory will be zero-initialized
--skip-pass,-sp
Skip a pass (do not run it)
Tool options: -------------
--mvp-features,-mvp
Disable all non-MVP features
--all-features,-all
Enable all features
--detect-features
(deprecated - this flag does nothing)
--quiet,-q
Emit less verbose output and hide trivial warnings.
--experimental-poppy
Parse wast files as Poppy IR for testing purposes.
--enable-sign-ext
Enable sign extension operations
--disable-sign-ext
Disable sign extension operations
--enable-threads
Enable atomic operations
--disable-threads
Disable atomic operations
--enable-mutable-globals
Enable mutable globals
--disable-mutable-globals
Disable mutable globals
--enable-nontrapping-float-to-int
Enable nontrapping float-to-int operations
--disable-nontrapping-float-to-int
Disable nontrapping float-to-int operations
--enable-simd
Enable SIMD operations and types
--disable-simd
Disable SIMD operations and types
--enable-bulk-memory
Enable bulk memory operations
--disable-bulk-memory
Disable bulk memory operations
--enable-exception-handling
Enable exception handling operations
--disable-exception-handling
Disable exception handling operations
--enable-tail-call
Enable tail call operations
--disable-tail-call
Disable tail call operations
--enable-reference-types
Enable reference types
--disable-reference-types
Disable reference types
--enable-multivalue
Enable multivalue functions
--disable-multivalue
Disable multivalue functions
--enable-gc
Enable garbage collection
--disable-gc
Disable garbage collection
--enable-memory64
Enable memory64
--disable-memory64
Disable memory64
--enable-relaxed-simd
Enable relaxed SIMD
--disable-relaxed-simd
Disable relaxed SIMD
--enable-extended-const
Enable extended const expressions
--disable-extended-const
Disable extended const expressions
--enable-strings
Enable strings
--disable-strings
Disable strings
--enable-multimemory
Enable multimemory
--disable-multimemory
Disable multimemory
--enable-typed-continuations
Enable typed continuations
--disable-typed-continuations
Disable typed continuations
--enable-shared-everything
Enable shared-everything threads
--disable-shared-everything
Disable shared-everything threads
--enable-fp16
Enable float 16 operations
--disable-fp16
Disable float 16 operations
--enable-typed-function-references
Deprecated compatibility flag
--disable-typed-function-references
Deprecated compatibility flag
--no-validation,-n
Disables validation, assumes inputs are correct
--pass-arg,-pa
An argument passed along to optimization passes being run. Must be in the form KEY@VALUE. If KEY
is the name of a pass then it applies to the closest instance of that pass before us. If KEY is
not the name of a pass then it is a global option that applies to all pass instances that read it.
--closed-world,-cw
Assume code outside of the module does not inspect or interact with GC and function references,
even if they are passed out. The outside may hold on to them and pass them back in, but not
inspect their contents or call them.
--preserve-type-order
Preserve the order of types from the input (useful for debugging and testing)
--generate-stack-ir
generate StackIR during writing
--optimize-stack-ir
optimize StackIR during writing
--print-stack-ir
print StackIR during writing
--no-stack-ir
do not use StackIR (even when it is the default)
General options: ----------------
--version
Output version information and exit
--help,-h
Show this help message and exit
--debug,-d
Print debug information to stderr
wasm-opt 120 April 2025 WASM-OPT(1)