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remove useless ident() functions in const tests #61658
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Original file line number | Diff line number | Diff line change |
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@@ -1,15 +1,16 @@ | ||
// run-pass | ||
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#![feature(ptr_internals, test)] | ||
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extern crate test; | ||
use test::black_box as b; // prevent promotion of the argument and const-propagation of the result | ||
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use std::ptr::NonNull; | ||
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const DANGLING: NonNull<u32> = NonNull::dangling(); | ||
const CASTED: NonNull<u32> = NonNull::cast(NonNull::<i32>::dangling()); | ||
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fn ident<T>(ident: T) -> T { | ||
ident | ||
} | ||
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pub fn main() { | ||
assert_eq!(DANGLING, ident(NonNull::dangling())); | ||
assert_eq!(CASTED, ident(NonNull::dangling())); | ||
assert_eq!(DANGLING, b(NonNull::dangling())); | ||
assert_eq!(CASTED, b(NonNull::dangling())); | ||
} |
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Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -1,15 +1,15 @@ | ||
// run-pass | ||
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#![feature(ptr_internals)] | ||
#![feature(ptr_internals, test)] | ||
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extern crate test; | ||
use test::black_box as b; // prevent promotion of the argument and const-propagation of the result | ||
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use std::ptr::Unique; | ||
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const PTR: *mut u32 = Unique::empty().as_ptr(); | ||
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fn ident<T>(ident: T) -> T { | ||
ident | ||
} | ||
const PTR: *mut u32 = Unique::empty().as_ptr(); | ||
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pub fn main() { | ||
assert_eq!(PTR, ident(Unique::<u32>::empty().as_ptr())); | ||
assert_eq!(PTR, b(Unique::<u32>::empty()).as_ptr()); | ||
} |
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hmm... does this actually have the desired effect? I think we need to do
b(NonNull::dangling as fn() -> NonNull<u32>)()
in order to guarantee that rustc won't const prop the value by itself.There was a problem hiding this comment.
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I don't think it is reasonable to fight against compiler optimizations like that here. I mean, it'll still get const-prop'ed by LLVM...
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IOW, this is not the const-prop test suite. Then anyway we'd have to do three-way comparison to check both the result with and without const-prop.
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const prop by LLVM is fine. The problem is that this is testing our const evaluator, and if the rhs is also computed by the const evaluator, then the comparison is moot.
I know it's not the const-prop test suite, it should not be testing const prop, it should be testing const eval against runtime. But with sufficiently smart const prop we'll get the rhs const propagated (at least the part inside the
b(..)
, const prop won't touchblack_box
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The comparison is still relevant as it is the const evaluator accessed through very different code paths. We have (at least) three ways the computation might go here and this only compares two of them, I see no good reason why comparing these two would be better than comparing the other two. The const-prop test suite will make sure they are the same.
But as you wish, I changed it. Lucky enough this does not need a type annotation.