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Add explicit arities to calls, breaks, & return #595

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Add explicit arities
rossberg Mar 8, 2016
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Merge branch 'master' into arities
rossberg Mar 24, 2016
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38 changes: 22 additions & 16 deletions BinaryEncoding.md
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Expand Up @@ -314,24 +314,26 @@ It is legal to have several entries with the same type.

## Control flow operators ([described here](AstSemantics.md#control-flow-structures))

| Name | Opcode | Immediate | Description |
| Name | Opcode | Immediates | Description |
| ---- | ---- | ---- | ---- |
| `nop` | `0x00` | | no operation |
| `block` | `0x01` | count = `varuint32` | a sequence of expressions, the last of which yields a value |
| `loop` | `0x02` | count = `varuint32` | a block which can also form control flow loops |
| `block` | `0x01` | count : `varuint32` | a sequence of expressions, the last of which yields a value |
| `loop` | `0x02` | count : `varuint32` | a block which can also form control flow loops |
| `if` | `0x03` | | high-level one-armed if |
| `if_else` | `0x04` | | high-level two-armed if |
| `select` | `0x05` | | select one of two values based on condition |
| `br` | `0x06` | relative_depth = `varuint32` | break that targets a outer nested block |
| `br_if` | `0x07` | relative_depth = `varuint32` | conditional break that targets a outer nested block |
| `br` | `0x06` | arity : `varuint32`, relative_depth : `varuint32` | break that targets a outer nested block |
| `br_if` | `0x07` | arity : `varuint32`, relative_depth : `varuint32` | conditional break that targets a outer nested block |
| `br_table` | `0x08` | see below | branch table control flow construct |
| `return` | `0x14` | | return zero or one value from this function |
| `return` | `0x14` | arity : `varuint32` | return zero or one value from this function |
| `unreachable` | `0x15` | | trap immediately |

All arities must be either 0 or 1 in the MVP.
The `br_table` operator has an immediate operand which is encoded as follows:

| Field | Type | Description |
| ---- | ---- | ---- |
| arity | `varuint32` | number of transfer arguments (0 or 1) |
| target_count | `varuint32` | number of targets in the target_table |
| target_table | `uint32*` | target entries that indicate an outer block or loop to which to break |
| default_target | `uint32` | an outer block or loop to which to break in the default case |
Expand All @@ -341,17 +343,21 @@ branches to the block or loop at the given offset within the `target_table`. If
out of range, `br_table` branches to the default target.

## Basic operators ([described here](AstSemantics.md#constants))
| Name | Opcode | Immediate | Description |

| Name | Opcode | Immediates | Description |
| ---- | ---- | ---- | ---- |
| `i32.const` | `0x0a` | value = `varint32` | a constant value interpreted as `i32` |
| `i64.const` | `0x0b` | value = `varint64` | a constant value interpreted as `i64` |
| `f64.const` | `0x0c` | value = `uint64` | a constant value interpreted as `f64` |
| `f32.const` | `0x0d` | value = `uint32` | a constant value interpreted as `f32` |
| `get_local` | `0x0e` | local_index = `varuint32` | read a local variable or parameter |
| `set_local` | `0x0f` | local_index = `varuint32` | write a local variable or parameter |
| `call` | `0x12` | function_index = `varuint32` | call a function by its index |
| `call_indirect` | `0x13` | signature_index = `varuint32` | call a function indirect with an expected signature |
| `call_import` | `0x1f` | import_index = `varuint32` | call an imported function by its index |
| `i32.const` | `0x0a` | value : `varint32` | a constant value interpreted as `i32` |
| `i64.const` | `0x0b` | value : `varint64` | a constant value interpreted as `i64` |
| `f64.const` | `0x0c` | value : `uint64` | a constant value interpreted as `f64` |
| `f32.const` | `0x0d` | value : `uint32` | a constant value interpreted as `f32` |
| `get_local` | `0x0e` | local_index : `varuint32` | read a local variable or parameter |
| `set_local` | `0x0f` | local_index : `varuint32` | write a local variable or parameter |
|
| `call` | `0x12` | arity : `varuint32`, function_index : `varuint32` | call a function by its index |
| `call_indirect` | `0x13` | arity : `varuint32`, signature_index : `varuint32` | call a function indirect with an expected signature |
| `call_import` | `0x1f` | arity : `varuint32`, import_index : `varuint32` | call an imported function by its index |

The arity immediates for the different call opcodes give the number of arguments.

## Memory-related operators ([described here](AstSemantics.md#linear-memory-accesses))

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