[Webkit-unassigned] [Bug 195808] New: [WHLSL] Implement loop expressions

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=195808

            Bug ID: 195808
           Summary: [WHLSL] Implement loop expressions
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebGPU
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mmaxfield at apple.com

We transform WHLSL expressions like "a < b * c" into something like:

auto temporary1 = b * c;
auto result = a < temporary1;

This works in the general case, but not if we have something like:

while (a < b * c) { ... }

MSL doesn't support lambdas, so we can't just throw the statements into a lambda.

There are two solutions to this problem:

1) Turn all loops into infinite loops, and emulate their expressions by emitting code in all the necessary places. So, something like:

while (true) {
    auto temporary1 = b * c;
    auto result = a < temporary1;
    if (!result)
        break;
}

2) Generate a functor class, passing in references to all referenced variables. So, something like:

class Functor {
    Functor(int& a, int& b, int& c) : a(a), b(b), c(c) {}
    bool operator()() {
        auto temporary1 = b * c;
        auto result = a < temporary1;
        return result;
    }

private:
    int& a;
    int& b;
    int& c;
};

while (Functor(a, b, c)()) {
   ...
}

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