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dawn-cmake/docs/tint/compound_statements.md
James Price 26ebe5ec36 tint: Refactor if-else statement representation 
Instead of using an `if` node that has a list of `else` statements,
make each `if` statement have a single optional `else` statement,
which may itself be an `if` statement (or just a block statement).

This better matches the WGSL grammar (now that we have removed
`elseif`), and simplifies various pieces of code that handle these
statements.

Change-Id: Ie4272f1422224490ac598a03aa8b4dd00ba03010
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/87940
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: James Price <jrprice@google.com>
2022-04-29 00:14:53 +00:00

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Compound Statements

Compound statements are statements that can hold other statements.

This document maps the WGSL compound statements to their semantic tree representations.

if statement

WGSL:

if (condition_a) {
    statement_a;
} else if (condition_b) {
    statement_b;
} else {
    statement_c;
}

Semantic tree:

sem::IfStatement {
    condition_a
    sem::BlockStatement {
        statement_a
    }
    sem::IfStatement {
        condition_b
        sem::BlockStatement {
            statement_b
        }
        sem::BlockStatement {
            statement_c
        }
    }
}

for loop

WGSL:

for (initializer; condition; continuing) {
    statement;
}

Semantic tree:

sem::ForLoopStatement {
    sem::Statement  initializer
    sem::Expression condition
    sem::Statement  continuing

    sem::LoopBlockStatement {
        sem::Statement statement
    }
}

loop

WGSL:

loop (condition) {
    statement_a;
    continuing {
        statement_b;
    }
}

Semantic tree:

sem::LoopStatement {
    sem::Expression condition

    sem::LoopBlockStatement {
        sem::Statement statement_a
        sem::LoopContinuingBlockStatement {
            sem::Statement statement_b
        }
    }
}

switch statement

WGSL:

switch (condition) {
    case literal_a, literal_b: {
        statement_a;
    }
    default {
        statement_b;
    }
}

Semantic tree:

sem::SwitchStatement {
    sem::Expression condition
    sem::CaseStatement {
        sem::BlockStatement {
            sem::Statement statement_a
        }
    }
    sem::CaseStatement {
        sem::BlockStatement {
            sem::Statement statement_b
        }
    }
}