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Adrien Leravat
d02366f881
Prevent copies when initializing value expression from reference expression. This is based on https://github.com/carbon-language/carbon-lang/pull/2006, which introduces expression categories, and how it is possible to convert to/from those different categories. Continuation of https://github.com/carbon-language/carbon-lang/pull/2907 ## Functional changes * Initializing a value expression from a reference expression takes its value without a copy * Reading from the value expression causes an error if the value changed from the time it was initialized * In this situation, prevents a copy both for variable definitions, and call parameter bindings ## Main implementation changes * Add new `ExpressionCategoryAction`, which evaluates an expression and returns an `ExpressionValue` containing its category and address (if any), in addition to the resulting `Value*` * `ExpressionAction`s now invokes `ExpressionCategoryAction` and unwraps the returned `ExpressionValue` * `RuntimeScope::BindAndPin` method, and corresponding when attempting to read a `value_node`. ## Next work * Avoid unnecessary copies from value expression to value expression, after ensuring that even value expression temporaries are registered for destruction (https://github.com/Pixep/carbon-lang/pull/9)