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Auto merge of #51833 - wesleywiser:faster_large_constant_arrays, r=ol…
…i-obk Speed up compilation of large constant arrays This is a different approach to #51672 as suggested by @oli-obk. Rather than write each repeated value one-by-one, we write the first one and then copy its value directly into the remaining memory. With this change, the [toy program](https://github.com/rust-lang/rust/blob/c2f4744d2db4e162df824d0bd0b093ba4b351545/src/test/run-pass/mir_heavy_promoted.rs) goes from 63 seconds to 19 seconds on my machine. Edit: Inlining `Size::bytes()` saves an additional 6 seconds dropping the total time to 13 seconds on my machine. Edit2: Now down to 2.8 seconds. r? @oli-obk cc @nnethercote @eddyb
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// Copyright 2018 The Rust Project Developers. See the COPYRIGHT | ||
// file at the top-level directory of this distribution and at | ||
// http://rust-lang.org/COPYRIGHT. | ||
// | ||
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
// option. This file may not be copied, modified, or distributed | ||
// except according to those terms. | ||
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#[derive(Copy, Clone)] | ||
union Foo { | ||
a: isize, | ||
b: (), | ||
} | ||
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enum Bar { | ||
Boo = [unsafe { Foo { b: () }.a }; 4][3], | ||
//~^ ERROR constant evaluation of enum discriminant resulted in non-integer | ||
} | ||
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fn main() { | ||
assert_ne!(Bar::Boo as isize, 0); | ||
} |
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// Copyright 2018 The Rust Project Developers. See the COPYRIGHT | ||
// file at the top-level directory of this distribution and at | ||
// http://rust-lang.org/COPYRIGHT. | ||
// | ||
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
// option. This file may not be copied, modified, or distributed | ||
// except according to those terms. | ||
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const FOO: isize = 42; | ||
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enum Bar { | ||
Boo = *[&FOO; 4][3], | ||
} | ||
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fn main() { | ||
assert_eq!(Bar::Boo as isize, 42); | ||
} |