Thanks to visit codestin.com
Credit goes to github.com

Skip to content

Add break-if as optional at end of continuing #2618

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 5 commits into from
Feb 25, 2022
Merged

Add break-if as optional at end of continuing #2618

Changes from 2 commits
Commits
Show all changes
5 commits
Select commit Hold shift + click to select a range
b5406bd
Add break-if as optional at end of continuing
dneto0 Feb 23, 2022
0e7a4ab
Add statement behaviour of break-if
dneto0 Feb 23, 2022
68eaf5d
Add uniformity analysis for break-if
dneto0 Feb 23, 2022
020bb30
Apply review feedback
dneto0 Feb 24, 2022
2016eaa
Avoid double-avoid
dneto0 Feb 24, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
84 changes: 48 additions & 36 deletions wgsl/index.bs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4984,6 +4984,12 @@ from the start of the next statement until the end of the compound statement.
| [=syntax/brace_left=] [=syntax/statement=] * [=syntax/brace_right=]
</div>

There are two special forms of compound statement:
* a [=syntax/continuing_compound_statement=] forms the body of a [[#continuing-statement|continuing]] statement,
and allows an optional [[#break-if-statement|break-if]] statement at the end.
* a [=syntax/case_compound_statement=] forms the body of a `case` or `default` clause in a [[#switch-statement|switch]] statement,
and allows an optional [=syntax/fallthrough_statement|fallthrough=] statement at the end.

## Assignment Statement ## {#assignment}

An <dfn noexport dfn-for="statement">assignment</dfn> evaluates an expression,
Expand Down Expand Up @@ -5338,19 +5344,22 @@ An `if` statement is executed as follows:
<div class='syntax' noexport='true'>
<dfn for=syntax>switch_body</dfn> :

| [=syntax/case=] [=syntax/case_selectors=] [=syntax/colon=] [=syntax/brace_left=] [=syntax/case_body=] ? [=syntax/brace_right=]
| [=syntax/case=] [=syntax/case_selectors=] [=syntax/colon=] [=syntax/case_compound_statement=]

| [=syntax/default=] [=syntax/colon=] [=syntax/brace_left=] [=syntax/case_body=] ? [=syntax/brace_right=]
| [=syntax/default=] [=syntax/colon=] [=syntax/case_compound_statement=]
</div>
<div class='syntax' noexport='true'>
<dfn for=syntax>case_selectors</dfn> :

| [=syntax/const_literal=] ( [=syntax/comma=] [=syntax/const_literal=] ) * [=syntax/comma=] ?
</div>
<div class='syntax' noexport='true'>
<dfn for=syntax>case_body</dfn> :
<dfn for=syntax>case_compound_statement</dfn> :

| [=syntax/statement=] [=syntax/case_body=] ?
| [=syntax/brace_left=] [=syntax/statement=] * [=syntax/fallthrough_statement=] ? [=syntax/brace_right=]
</div>
<div class='syntax' noexport='true'>
<dfn for=syntax>fallthrough_statement</dfn> :

| [=syntax/fallthrough=] [=syntax/semicolon=]
</div>
Expand Down Expand Up @@ -5609,19 +5618,13 @@ The following statement forms are equivalent:
A <dfn noexport dfn-for="statement">break</dfn> statement transfers control to the first statement
after the body of the nearest-enclosing [=statement/loop=]
or [=statement/switch=] statement.
A `break` statement must only be used within [=statement/loop=], [=statement/for=], and [=statement/switch=] statements.

When a `break` statement is placed such that it would exit from a loop's [=statement/continuing=] statement,
then:
A `break` statement must only be used within [=statement/loop=], [=statement/for=], and [=statement/switch=] statements.

* The `break` statement must appear as either:
* The only statement in the `if` clause of an `if` statement that has:
* no `else` clause or an empty `else` clause
* no `else if` clauses
* The only statement in the `else` clause of an `if` statement that has an empty `if` clause and no `else if` clauses.
* That `if` statement must appear last in the `continuing` clause.
A `break` statement must not placed such that it would exit from a loop's [[#continuing-statement|continuing]] statement.
Use a [[#break-if-statement|break-if]] statement instead.

<div class='example wgsl function-scope' heading="WGSL Valid loop if-break from a continuing clause">
<div class='example wgsl function-scope' heading="WGSL Invalid loop break from a continuing clause">
<xmp>
var a: i32 = 2;
var i: i32 = 0;
Expand All @@ -5634,36 +5637,30 @@ then:

continuing {
i = i + step;
if i >= 4 { break; }
if i >= 4 { break; } // Invalid. Use break-if instead.
}
}
</xmp>
</div>

<div class='example wgsl function-scope' heading="WGSL Valid loop if-else-break from a continuing clause">
<xmp>
var a: i32 = 2;
var i: i32 = 0;
loop {
let step: i32 = 1;
### Break-If Statement ### {#break-if-statement}

if i % 2 == 0 { continue; }

a = a * 2;
<div class='syntax' noexport='true'>
<dfn for=syntax>break_if_statement</dfn> :

continuing {
i = i + step;
if i < 4 {} else { break; }
}
}
</xmp>
| [=syntax/break=] [=syntax/if=] [=syntax/expression=] [=syntax/semicolon=]
</div>

<div class='example wgsl function-scope expect-error' heading="WGSL Invalid breaks from a continuing clause">
A <dfn noexport dfn-for="statement">break-if</dfn> statement evaluates a boolean condition, and if the condition
is true, transfers control to the first statement after the body of the nearest-enclosing [=statement/loop=] statement.
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Nit: this seems a bit wrong for a loop nested in a continuing block. Also an existing problem for regular breaks.

loop {
  if (c1) { break; }
  continuing {
    loop {
      continuing {
        break if c2;
      }
    }
  }
}
let x = 5; // This is the first statement after the inner loop

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Fixed it here and for a regular break, which had the same problem.


Note: A break-if statement may only appear as the last statement in the body of a [[#continuing-statement|continuing]]
statement.

<div class='example wgsl function-scope' heading="WGSL Valid loop break-if from a continuing clause">
<xmp>
var a: i32 = 2;
var i: i32 = 0;

loop {
let step: i32 = 1;

Expand All @@ -5673,9 +5670,7 @@ then:

continuing {
i = i + step;
break; // Invalid: too early
if i < 4 { i++; } else { break; } // Invalid: if is too complex, and too early
if i >= 4 { break; } else { i++; } // Invalid: if is too complex
break if i >= 4;
}
}
</xmp>
Expand Down Expand Up @@ -5724,7 +5719,13 @@ control past a declaration used in the targeted [=statement/continuing=] stateme
<div class='syntax' noexport='true'>
<dfn for=syntax>continuing_statement</dfn> :

| [=syntax/continuing=] [=syntax/compound_statement=]
| [=syntax/continuing=] [=syntax/continuing_compound_statement=]
</div>

<div class='syntax' noexport='true'>
<dfn for=syntax>continuing_compound_statement</dfn> :

| [=syntax/brace_left=] [=syntax/statement=] * [=syntax/break_if_statement=] ? [=syntax/brace_right=]
</div>

A <dfn dfn-for="statement">continuing</dfn> statement specifies a [=compound statement=] to be executed at the end of a loop [=iteration=].
Expand Down Expand Up @@ -5818,6 +5819,8 @@ Note: If the function [=return value|returns a value=], that value is ignored.

## Statements Grammar Summary ## {#statements-summary}

The [=syntax/statement=] rule matches statements that can be used in most places inside a function body.

<div class='syntax' noexport='true'>
<dfn for=syntax>statement</dfn> :

Expand Down Expand Up @@ -5854,6 +5857,11 @@ Note: If the function [=return value|returns a value=], that value is ignored.
| [=syntax/decrement_statement=] [=syntax/semicolon=]
</div>

Additionally, certain statements may only be used in very specific contexts:
* [=syntax/break_if_statement=]
* [=syntax/case_compound_statement=]
* [=syntax/continuing_compound_statement=]
* [=syntax/fallthrough_statement=]

## Statements Behavior Analysis ## {#behaviors}

Expand Down Expand Up @@ -5959,6 +5967,10 @@ The reason is that only functions without a return type can have such a [=behavi
<td>break;
<td>
<td>{Break}
<tr algorithm="break if behavior">
<td>break if |e|;
<td class="nowrap">|e|: |B|
<td>|B| &cup; {Break}
<tr algorithm="continue behavior">
<td>continue;
<td>
Expand Down