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Reorder select's operands to put the condition last. #489

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sunfishcode merged 2 commits into from
Jan 28, 2016
Merged

Reorder select's operands to put the condition last. #489

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1bfcecb
Reorder select's operands to put the condition last.
sunfishcode Dec 2, 2015
e9eeffc
Specify that branch instructions' return value operands come first.
sunfishcode Dec 2, 2015
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13 changes: 7 additions & 6 deletions AstSemantics.md
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Expand Up @@ -246,14 +246,16 @@ a value and may appear as children of other expressions.
### Branches and nesting

The `br` and `br_if` constructs express low-level branching.
Branches that exit a `block`, `loop`, or `tableswitch` may take a subexpression
that yields a value for the exited construct.
Branches may only reference labels defined by an outer *enclosing construct*.
This means that, for example, references to a `block`'s label can only occur
within the `block`'s body. In practice, outer `block`s can be used to place labels for any
given branching pattern, except for one restriction: one can't branch into the middle of a
loop from outside it. This restriction ensures all control flow graphs are well-structured.

Branches that exit a `block`, `loop`, or `tableswitch` may take a subexpression
that yields a value for the exited construct. If present, it is the first operand
before any others.

### Yielding values from control constructs

The `nop`, `if`, `br`, `br_if`, `case`, and `return` constructs do not yield values.
Expand Down Expand Up @@ -550,10 +552,9 @@ outside the range which rounds to an integer in range) traps.

## Type-parameterized operators.

* `select`: a ternary operator with a boolean (i32) condition and two
additional operands, which must have the same type as each other. `select`
returns the the first of these two operands if the condition operand is
non-zero, or the second otherwise.
* `select`: a ternary operator with two operands, which have the same type as
each other, plus a boolean (i32) condition. `select` returns the first
operand if the condition operand is non-zero, or the second otherwise.

## Feature test

Expand Down