No Aliasing Allowed With Pointer Paramters

Pointer parameters to user-declared functions are not allowed to alias when there is a potential write via the pointer or its alias.

In more detail, shader creation fails if:

a pointer is passed as an argument to user-declared function, and
the called function, or one of the stack of functions it may call, has two views (pointer, reference, or both) into the same original variable, and
there is a potential write via one of those views.

The check for a potential write is a static analysis, ignoring control flow.

The code sample shows valid and invalid cases where a helper function writes via a pointer parameter p, but reads from a module-scope variable x. It is an error for p to alias x.

var<private> x: i32; var<private> y: i32; fn set_from_x(p : ptr<private, i32>) { *p = x; // Writes via p, reads via module-scoped x. } // Alias analysis ignores control flow, so the analysis thinks this // function writes via p, and reads via module-scoped x. fn dont_set_from_x(p : ptr<private, i32>) { if (false) { *p = x; // Still counts as a potential write. } } fn main() { // set_from_x(&x); // Error: set_from_x would have two views of x. // There would be a write x through *p // dont_set_from_x(&x); // Still an error. // But this is fine, since x and y don't alias. set_from_x(&y); }