WebAssembly/Instructions

This page is created because it's annoying to constantly jump around the official WebAssembly documentation.

The page requires careful review as official specs are updated

Instructions

Instruction	Byte Code	Execution	Notes
unreachable	$00	1. Trap
nop	$01	1. Do nothing
block	$02 blocktype	1. Let n be the arity |t?| of the result type t?. 2. Let L be the label whose arity is n and whose continuation is the end of the block. 3. Enter the block instr∗ with label L.	block must always be closed with end
loop	$03
if	$04
else	$05		can only be used with if. Only single else is allowed per if
(reserved)	$06..$0A
end	$0B		end can only close block or loop clocks
br labelidx	$0C labelidx	1. Assert: due to validation, the stack contains at least l+1 labels. 2. Let L be the l-th label appearing on the stack, starting from the top and counting from zero. 3. Let n be the arity of L. 4. Assert: due to validation, there are at least n values on the top of the stack. 5. Pop the values valn from the stack. 6. Repeat l+1 times: a. While the top of the stack is a value, do: i. Pop the value from the stack. b. Assert: due to validation, the top of the stack now is a label. c. Pop the label from the stack. 7. Push the values valn to the stack. 8. Jump to the continuation of L.	Branching - Unconditional Branching is possible only within a block. The block itself defines labels where the branching can go to.
br_if labelidx	$0D labelidx	1. Assert: due to validation, a value of value type i32 is on the top of the stack. 2. Pop the value i32.const c from the stack. 3. If c is non-zero, then: a. Execute the instruction (br l). 4. Else: b. Do nothing.	Branching - Conditional Branching is possible only within a block. The block itself defines labels where the branching can go to.
br_table vec(labelidxI) labelidx	$0E
return	$0F
call funcidx	$10	1. Let F be the current frame. 2. Assert: due to validation, F.module.funcaddrs[x] exists. 3. Let a be the function address F.module.funcaddrs[x]. 4. Invoke the function instance at address a.
call_indirect typeuse	$11	1. Let F be the current frame. 2. Assert: due to validation, F.module.tableaddrs[0] exists. 3. Let ta be the table address F.module.tableaddrs[0]. 4. Assert: due to validation, S.tables[ta] exists. 5. Let tab be the table instance S.tables[ta]. 6. Assert: due to validation, F.module.types[x] exists. 7. Let ftexpect be the function type F.module.types[x]. 8. Assert: due to validation, a value with value type i32 is on the top of the stack. 9. Pop the value i32.const i from the stack. 10. If i is not smaller than the length of tab.elem, then: a. Trap. 11. If tab.elem[i] is uninitialized, then: a. Trap. 12. Let a be the function address tab.elem[i]. 13. Assert: due to validation, S.funcs[a] exists. 14. Let f be the function instance S.funcs[a]. 15. Let ftactual be the function type f.type. 16. If ftactual and ftexpect differ, then: a. Trap. 17. Invoke the function instance at address a.	Note that call_indirect text syntax is different: call_indirect (type x) A plain numeric value is treated as table number, not function signature. The signature can also be explicitly specified call_indirect (param i32)(param f32)(result f64) In this case the assembly would assign the proper type.
(reserved)	$12..$19
drop	$1A	[t]→[]
select	$1B	[t t i32]→[t]
(reserved)	$1C..$1F
local.get x	$20
local.set x	$21
local.tee x	$22
global.get x	$23
global.set x	$24
(reserved)	$25..$27
i32.load memarg	$28	t.load memarg and t.loadN_sx memarg 1. Let F be the current frame. 2. Assert: due to validation, F.module.memaddrs[0] exists. 3. Let a be the memory address F.module.memaddrs[0]. 4. Assert: due to validation, S.mems[a] exists. 5. Let mem be the memory instance S.mems[a]. 6. Assert: due to validation, a value of value type i32 is on the top of the stack. 7. Pop the value i32.const i from the stack. 8. Let ea be the integer i+memarg.offset. 9. If N is not part of the instruction, then: a. Let N be the bit width |t| of value type t. 10. If ea+N/8 is larger than the length of mem.data, then: a. Trap. 11. Let b∗ be the byte sequence mem.data[ea:N/8]. 12. If N and sx are part of the instruction, then: a. Let n be the integer for which bytesiN(n)=b∗. b. Let c be the result of computing extend_sxN,|t|(n). 13. Else: a. Let c be the constant for which bytest(c)=b∗. 14. Push the value t.const c to the stack.
i64.load memarg	$29
f32.load memarg	$2A
f64.load memarg	$2B
i32.load8_s memarg	$2C
i32.load8_u memarg	$2D
i32.load16_s memarg	$2E
i32.load16_u memarg	$2F
i64.load8_s memarg	$30
i64.load8_u memarg	$31
i64.load16_s memarg	$32
i64.load16_u memarg	$33
i64.load32_s memarg	$34
i64.load32_u memarg	$35
i32.store memarg	$36	t.store memarg and t.storeN memarg 1. Let F be the current frame. 2. Assert: due to validation, F.module.memaddrs[0] exists. 3. Let a be the memory address F.module.memaddrs[0]. 4. Assert: due to validation, S.mems[a] exists. 5. Let mem be the memory instance S.mems[a]. 5. Assert: due to validation, a value of value type t is on the top of the stack. 7. Pop the value t.const c from the stack. 8. Assert: due to validation, a value of value type i32 is on the top of the stack. 9. Pop the value i32.const i from the stack. 10. Let ea be the integer i+memarg.offset. 11. If N is not part of the instruction, then: a. Let N be the bit width |t| of value type t. 12. If ea+N/8 is larger than the length of mem.data, then: a. Trap. 13. If N is part of the instruction, then: a. Let n be the result of computing wrap|t|,N(c). b. Let b∗ be the byte sequence bytesiN(n). 14. Else: a. Let b∗ be the byte sequence bytest(c). 15. Replace the bytes mem.data[ea:N/8] with b∗.
i64.store memarg	$37
f32.store memarg	$38
f64.store memarg	$39
i32.store8 memarg	$3A
i32.store16 memarg	$3B
i64.store8 memarg	$3C
i64.store16 memarg	$3D
i64.store32 memarg	$3E
memory.size	$3F
memory.grow	$40
i32.const i32	$41
i64.const i64	$42
f32.const f32	$43
f64.const f64	$44
i32.eqz	$45		Return 1 if i is zero, 0 otherwise.
i32.eq	$46		Return 1 if i1 equals i2, 0 otherwise.
i32.ne	$47		Return 1 if i1 does not equal i2, 0 otherwise.
i32.lt_s	$48		Let j1 be the signed interpretation of i1. Let j2 be the signed interpretation of i2. Return 1 if j1 is less than j2, 0 otherwise.
i32.lt_u	$49		Return 1 if i1 is less than i2, 0 otherwise.
i32.gt_s	$4A
i32.gt_u	$4B
i32.le_s	$4C
i32.le_u	$4D
i32.ge_s	$4E
i32.ge_u	$4F
i64.eqz	$50		Return 1 if i is zero, 0 otherwise.
i64.eq	$51		Return 1 if i1 equals i2, 0 otherwise.
i64.ne	$52		Return 1 if i1 does not equal i2, 0 otherwise.
i64.lt_s	$53		Let j1 be the signed interpretation of i1. Let j2 be the signed interpretation of i2. Return 1 if j1 is less than j2, 0 otherwise.
i64.lt_u	$54		Return 1 if i1 is less than i2, 0 otherwise.
i64.gt_s	$55
i64.gt_u	$56
i64.le_s	$57
i64.le_u	$58
i64.ge_s	$59
i64.ge_u	$5A
f32.eq	$5B		Return 1 if i1 equals i2, 0 otherwise.
f32.ne	$5C		Return 1 if i1 does not equal i2, 0 otherwise.
f32.lt	$5D
f32.gt	$5E
f32.le	$5F
f32.ge	$60
f64.eq	$61		Return 1 if i1 equals i2, 0 otherwise.
f64.ne	$62		Return 1 if i1 does not equal i2, 0 otherwise.
f64.lt	$63
f64.gt	$64
f64.le	$65
f64.ge	$66
i32.clz	$67
i32.ctz	$68
i32.popcnt	$69
i32.add	$6A
i32.sub	$6B
i32.mul	$6C
i32.div_s	$6D
i32.div_u	$6E
i32.rem_s	$6F
i32.rem_u	$70
i32.and	$71
i32.or	$72
i32.xor	$73
i32.shl	$74
i32.shr_s	$75
i32.shr_u	$76
i32.rotl	$77
i32.rotr	$78
i64.clz	$79
i64.ctz	$7A
i64.popcnt	$7B
i64.add	$7C
i64.sub	$7D
i64.mul	$7E
i64.div_s	$7F
i64.div_u	$80
i64.rem_s	$81
i64.rem_u	$82
i64.and	$83
i64.or	$84
i64.xor	$85
i64.shl	$86
i64.shr_s	$87
i64.shr_u	$88
i64.rotl	$89
i64.rotr	$8A
f32.abs	$8B
f32.neg	$8C
f32.ceil	$8D
f32.floor	$8E
f32.trunc	$8F
f32.nearest	$90
f32.sqrt	$91
f32.add	$92
f32.sub	$93
f32.mul	$94
f32.div	$95
f32.min	$96
f32.max	$97
f32.copysign	$98
f64.abs	$99
f64.neg	$9A
f64.ceil	$9B
f64.floor	$9C
f64.trunc	$9D
f64.nearest	$9E
f64.sqrt	$9F
f64.add	$A0
f64.sub	$A1
f64.mul	$A2
f64.div	$A3
f64.min	$A4
f64.max	$A5
f64.copysign	$A6
i32.wrap_i64	$A7
i32.trunc_f32_s	$A8
i32.trunc_f32_u	$A9
i32.trunc_f64_s	$AA
i32.trunc_f64_u	$AB
i64.extend_i32_s	$AC
i64.extend_i32_u	$AD
i64.trunc_f32_s	$AE
i64.trunc_f32_u	$AF
i64.trunc_f64_s	$B0
i64.trunc_f64_u	$B1
f32.convert_i32_s	$B2
f32.convert_i32_u	$B3
f32.convert_i64_s	$B4
f32.convert_i64_u	$B5
f32.demote_f64	$B6
f64.convert_i32_s	$B7
f64.convert_i32_u	$B8
f64.convert_i64_s	$B9
f64.convert_i64_u	$BA
f64.promote_f32	$BB
i32.reinterpret_f32	$BC
i64.reinterpret_f64	$BD
f32.reinterpret_i32	$BE
f64.reinterpret_i64	$BF

See Also

• WebAssembly
• http://webassembly.github.io/spec/core/intro/index.html - official documentation