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Add fence instruction and encoding to overview #141

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Jul 8, 2019
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Add fence instruction and encoding to overview #141

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Add fence instruction and encoding to overview
conrad-watt Jun 19, 2019
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pack 0x0_ group densely
conrad-watt Jun 19, 2019
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conrad-watt Jun 19, 2019
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10 changes: 10 additions & 0 deletions proposals/threads/Overview.md
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Expand Up @@ -437,6 +437,12 @@ For the web embedding, `atomic.notify` is equivalent in behavior to executing th
1. Let `result` be [`Atomics.notify`][](`int32array`, `address`, `fcount`).
1. Return `result` converted to an `i32`.

## Fence operator

The fence operator, `atomic.fence`, takes no operands, and returns nothing. It is intended to preserve the semantics of the [fence operators of higher-level languages](https://en.cppreference.com/w/cpp/atomic/atomic_thread_fence).

Unlike other atomic operators, `atomic.fence` does not target a particular linear memory, and it is therefore *not* a validation error for this operator to be used in a module that does not declare a shared memory.
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nit: I assume it's also OK to be used in a module that declares no memory at all.

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yes; clarified this


## [JavaScript API][] changes

### `WebAssembly.Memory` Constructor
Expand Down Expand Up @@ -567,6 +573,8 @@ instr ::= ... |
inn.atomic.wait memarg |
atomic.notify memarg |

atomic.fence |

inn.atomic.load memarg | inn.atomic.store memarg |
inn.atomic.load8_u memarg | inn.atomic.load16_u memarg | i64.atomic.load32_u memarg |
inn.atomic.store8 memarg | inn.atomic.store16 memarg | i64.atomic.store32 memarg |
Expand All @@ -590,6 +598,8 @@ instr ::= ...
| 0xFE 0x01 m:memarg32 => i32.atomic.wait m
| 0xFE 0x02 m:memarg64 => i64.atomic.wait m

| 0xFE 0x0F 0x00 => atomic.fence
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| 0xFE 0x10 m:memarg32 => i32.atomic.load m
| 0xFE 0x11 m:memarg64 => i64.atomic.load m
| 0xFE 0x12 m:memarg8 => i32.atomic.load8_u m
Expand Down