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https://github.com/carbon-language/carbon-lang.git
synced 2026-09-24 20:30:14 +01:00
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)
28 lines
671 B
Plaintext
28 lines
671 B
Plaintext
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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// AUTOUPDATE
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// CHECK:STDOUT: a: 2
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// CHECK:STDOUT: a_pinned2: 1
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// CHECK:STDOUT: result: 0
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package ExplorerTest api;
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fn Main() -> i32 {
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var a: i32 = 1;
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let a_pinned: i32 = a;
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let a_pinned_copy: i32 = a_pinned;
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// OK: Value unused after being mutated.
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a = 2;
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Print("a: {0}", a);
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// OK: Value was copied from `a_pinned`, and reflects previous value.
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// TODO: Avoid value->value copy when possible.
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Print("a_pinned2: {0}", a_pinned_copy);
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return 0;
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}
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