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Make continuations consistently "shallow" (#874)

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Prior to this change, `__await` would make a deep copy of the continuation stack, but shallow-copy the individual stack frames within it. As a result, continuations appeared to have shallow semantics so long as the continuation stack had only a single frame.

This change also removes an obsolete test from the brief period when we intended continuations to have deep-copy semantics, which has been passing basically by accident.
This commit is contained in:
Geoff Romer
2021-10-11 14:57:09 -07:00
committed by GitHub
parent 9211c98951
commit d177a08e01
5 changed files with 34 additions and 52 deletions
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executable_semantics/testdata/experimental_continuation/copy_in_continuation.carbon
Vendored
-32
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@@ -1,32 +0,0 @@
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// RUN: executable_semantics %s 2>&1 | \
// RUN: FileCheck --match-full-lines --allow-unused-prefixes=false %s
// RUN: executable_semantics --trace %s 2>&1 | \
// RUN: FileCheck --match-full-lines --allow-unused-prefixes %s
// AUTOUPDATE: executable_semantics %s
// CHECK: result: 3
package ExecutableSemanticsTest api;
// Test the way in which copying of continuations interacts with data
// on the stack such as the variable `x`. In this example the copy
// happens after the variable `x` is created.
var y: i32 = 0;
fn main() -> i32 {
__continuation k1 {
var x: i32 = 0;
x = x + 1;
__await;
x = x + 2;
y = x;
}
__run k1;
var k2: __Continuation = k1;
__run k2;
return y;
}
executable_semantics/testdata/experimental_continuation/shallow_copy.carbon
Vendored
+9 -4
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@@ -14,12 +14,17 @@ package ExecutableSemanticsTest api;
// Assignment for continuations is shallow, so `k2` refers to the same
// continuation as `k1`.
var x: i32 = 0;
fn Foo() {
x = x + 1;
__await;
x = x + 2;
}
fn main() -> i32 {
var x: i32 = 0;
__continuation k1 {
x = x + 1;
__await;
x = x + 2;
Foo();
}
var k2: __Continuation = k1;
__run k1;