Add a bunch of tests for #107975

tests/ui/codegen/equal-pointers-unequal/README.md

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+See https://github.com/rust-lang/rust/issues/107975
+
+Basically, if you have two pointers with the same address but from two different allocations,
+the compiler gets confused whether their addresses are equal or not,
+resulting in some self-contradictory behavior of the compiled code.
+
+This folder contains some examples.
+They all boil down to allocating a variable on the stack, taking its address,
+getting rid of the variable, and then doing it all again.
+This way we end up with two addresses stored in two `usize`s (`a` and `b`).
+The addresses are (probably) equal but (definitely) come from two different allocations.
+Logically, we would expect that exactly one of the following options holds true:
+1. `a == b`
+2. `a != b`
+Sadly, the compiler does not always agree.
+
+Due to Rust having at least three meaningfully different ways
+to get a variable's address as an `usize`,
+each example is provided in three versions, each in the corresponding subfolder:
+1. `./as-cast/` for `&v as *const _ as usize`,
+2. `./strict-provenance/` for `addr_of!(v).addr()`,
+2. `./exposed-provenance/` for `addr_of!(v).expose_provenance()`.

tests/ui/codegen/equal-pointers-unequal/as-cast/basic.rs

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+//@ known-bug: #107975
+//@ run-pass
+
+fn main() {
+    let a: usize = {
+        let v = 0u8;
+        &v as *const _ as usize
+    };
+    let b: usize = {
+        let v = 0u8;
+        &v as *const _ as usize
+    };
+
+    // `a` and `b` are not equal.
+    assert_ne!(a, b);
+    // But they are the same number.
+    assert_eq!(format!("{a}"), format!("{b}"));
+    // And they are equal.
+    assert_eq!(a, b);
+}

tests/ui/codegen/equal-pointers-unequal/as-cast/function.rs

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+//@ known-bug: #107975
+//@ run-pass
+
+// Based on https://github.com/rust-lang/rust/issues/107975#issuecomment-1434203908
+
+fn f() -> usize {
+    let v = 0;
+    &v as *const _ as usize
+}
+
+fn main() {
+    let a = f();
+    let b = f();
+
+    // `a` and `b` are not equal.
+    assert_ne!(a, b);
+    // But they are the same number.
+    assert_eq!(format!("{a}"), format!("{b}"));
+    // And they are equal.
+    assert_eq!(a, b);
+}

tests/ui/codegen/equal-pointers-unequal/as-cast/inline1.rs

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+//@ known-bug: #107975
+//@ run-pass
+//@ check-run-results
+//@ normalize-stdout-test: "\d+" -> "<..>"
+
+// Based on https://github.com/rust-lang/rust/issues/107975#issuecomment-1432161340
+
+#[inline(never)]
+fn cmp(a: usize, b: usize) -> bool {
+    a == b
+}
+
+#[inline(always)]
+fn cmp_in(a: usize, b: usize) -> bool {
+    a == b
+}
+
+fn main() {
+    let a = {
+        let v = 0;
+        &v as *const _ as usize
+    };
+    let b = {
+        let v = 0;
+        &v as *const _ as usize
+    };
+    println!("{a:?} == {b:?} -> ==: {}, cmp_in: {}, cmp: {}", a == b, cmp_in(a, b), cmp(a, b));
+    assert_eq!(a.to_string(), b.to_string());
+}

tests/ui/codegen/equal-pointers-unequal/as-cast/inline1.run.stdout

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+<..> == <..> -> ==: false, cmp_in: false, cmp: true

tests/ui/codegen/equal-pointers-unequal/as-cast/inline2.rs

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+//@ known-bug: #107975
+//@ run-pass
+//@ check-run-results
+//@ normalize-stdout-test: "\d+" -> "<..>"
+
+// Based on https://github.com/rust-lang/rust/issues/107975#issuecomment-1432161340
+
+#[inline(never)]
+fn cmp(a: usize, b: usize) -> bool {
+    a == b
+}
+
+#[inline(always)]
+fn cmp_in(a: usize, b: usize) -> bool {
+    a == b
+}
+
+fn main() {
+    let a = {
+        let v = 0;
+        &v as *const _ as usize
+    };
+    let b = {
+        let v = 0;
+        &v as *const _ as usize
+    };
+    assert_eq!(a.to_string(), b.to_string());
+    println!("{a:?} == {b:?} -> ==: {}, cmp_in: {}, cmp: {}", a == b, cmp_in(a, b), cmp(a, b));
+}

tests/ui/codegen/equal-pointers-unequal/as-cast/inline2.run.stdout

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+<..> == <..> -> ==: true, cmp_in: true, cmp: true

tests/ui/codegen/equal-pointers-unequal/as-cast/print.rs

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+//@ known-bug: #107975
+//@ run-pass
+//@ check-run-results
+//@ normalize-stdout-test: "\d+" -> "<..>"
+
+// https://github.com/rust-lang/rust/issues/107975#issuecomment-1430704499
+
+fn main() {
+    let a = {
+        let v = 0;
+        &v as *const _ as usize
+    };
+    let b = {
+        let v = 0;
+        &v as *const _ as usize
+    };
+
+    println!("{}", a == b); // prints false
+    println!("{a}"); // or b
+    println!("{}", a == b); // prints true
+}

tests/ui/codegen/equal-pointers-unequal/as-cast/print.run.stdout

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+false
+<..>
+true

tests/ui/codegen/equal-pointers-unequal/as-cast/print3.rs

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+//@ known-bug: #107975
+//@ run-pass
+//@ check-run-results
+//@ normalize-stdout-test: "\d+" -> "<..>"
+
+// https://github.com/rust-lang/rust/issues/107975#issuecomment-1430704499
+
+fn main() {
+    let a = {
+        let v = 0;
+        &v as *const _ as usize
+    };
+    let b = {
+        let v = 0;
+        &v as *const _ as usize
+    };
+
+    println!("{}", a == b); // false
+    println!("{}", a == b); // false
+    let c = a;
+    println!("{} {} {}", a == b, a == c, b == c); // false true false
+    println!("{a} {b}");
+    println!("{} {} {}", a == b, a == c, b == c); // true true true
+}

tests/ui/codegen/equal-pointers-unequal/as-cast/print3.run.stdout

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+false
+false
+false true false
+<..> <..>
+true true true

tests/ui/codegen/equal-pointers-unequal/as-cast/segfault.rs

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+//@ known-bug: #107975
+//@ run-fail
+//@ check-run-results
+//@ compile-flags: -Copt-level=3
+
+// This one should segfault.
+// I don't know a better way to check for segfault other than
+// check that it fails and that the output is empty.
+
+// https://github.com/rust-lang/rust/issues/107975#issuecomment-1431758601
+
+use std::cell::RefCell;
+
+fn main() {
+    let a = {
+        let v = 0u8;
+        &v as *const _ as usize
+    };
+    let b = {
+        let v = 0u8;
+        &v as *const _ as usize
+    };
+    let i = b - a;
+    let arr = [
+        RefCell::new(Some(Box::new(1))),
+        RefCell::new(None),
+        RefCell::new(None),
+        RefCell::new(None),
+    ];
+    assert_ne!(i, 0);
+    let r = arr[i].borrow();
+    let r = r.as_ref().unwrap();
+    *arr[0].borrow_mut() = None;
+    println!("{}", *r);
+}

tests/ui/codegen/equal-pointers-unequal/as-cast/zero.rs

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+//@ known-bug: #107975
+//@ run-pass
+
+// Derived from https://github.com/rust-lang/rust/issues/107975#issuecomment-1431758601
+
+fn main() {
+    let a: usize = {
+        let v = 0u8;
+        &v as *const _ as usize
+    };
+    let b: usize = {
+        let v = 0u8;
+        &v as *const _ as usize
+    };
+
+    // So, are `a` and `b` equal?
+
+    // Let's check their difference.
+    let i: usize = a - b;
+    // It's not zero, which means `a` and `b` are not equal.
+    assert_ne!(i, 0);
+    // But it looks like zero...
+    assert_eq!(i.to_string(), "0");
+    // ...and now it *is* zero?
+    assert_eq!(i, 0);
+    // So `a` and `b` are equal after all?
+}

tests/ui/codegen/equal-pointers-unequal/exposed-provenance/basic.rs

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+//@ known-bug: #107975
+//@ run-pass
+
+#![feature(exposed_provenance)]
+
+use std::ptr::addr_of;
+
+fn main() {
+    let a: usize = {
+        let v = 0u8;
+        addr_of!(v).expose_provenance()
+    };
+    let b: usize = {
+        let v = 0u8;
+        addr_of!(v).expose_provenance()
+    };
+
+    // `a` and `b` are not equal.
+    assert_ne!(a, b);
+    // But they are the same number.
+    assert_eq!(format!("{a}"), format!("{b}"));
+    // And they are equal.
+    assert_eq!(a, b);
+}

tests/ui/codegen/equal-pointers-unequal/exposed-provenance/function.rs

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+//@ known-bug: #107975
+//@ run-pass
+
+// Based on https://github.com/rust-lang/rust/issues/107975#issuecomment-1434203908
+
+#![feature(exposed_provenance)]
+
+use std::ptr::addr_of;
+
+fn f() -> usize {
+    let v = 0;
+    addr_of!(v).expose_provenance()
+}
+
+fn main() {
+    let a = f();
+    let b = f();
+
+    // `a` and `b` are not equal.
+    assert_ne!(a, b);
+    // But they are the same number.
+    assert_eq!(format!("{a}"), format!("{b}"));
+    // And they are equal.
+    assert_eq!(a, b);
+}

tests/ui/codegen/equal-pointers-unequal/exposed-provenance/inline1.rs

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+//@ known-bug: #107975
+//@ run-pass
+//@ check-run-results
+//@ normalize-stdout-test: "\d+" -> "<..>"
+
+// Based on https://github.com/rust-lang/rust/issues/107975#issuecomment-1432161340
+
+
+#![feature(exposed_provenance)]
+
+use std::ptr::addr_of;
+
+#[inline(never)]
+fn cmp(a: usize, b: usize) -> bool {
+    a == b
+}
+
+#[inline(always)]
+fn cmp_in(a: usize, b: usize) -> bool {
+    a == b
+}
+
+fn main() {
+    let a = {
+        let v = 0;
+        addr_of!(v).expose_provenance()
+    };
+    let b = {
+        let v = 0;
+        addr_of!(v).expose_provenance()
+    };
+    println!("{a:?} == {b:?} -> ==: {}, cmp_in: {}, cmp: {}", a == b, cmp_in(a, b), cmp(a, b));
+    assert_eq!(a.to_string(), b.to_string());
+}

tests/ui/codegen/equal-pointers-unequal/exposed-provenance/inline1.run.stdout

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+<..> == <..> -> ==: false, cmp_in: false, cmp: true

tests/ui/codegen/equal-pointers-unequal/exposed-provenance/inline2.rs

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+//@ known-bug: #107975
+//@ run-pass
+//@ check-run-results
+//@ normalize-stdout-test: "\d+" -> "<..>"
+
+// Based on https://github.com/rust-lang/rust/issues/107975#issuecomment-1432161340
+
+#![feature(exposed_provenance)]
+
+use std::ptr::addr_of;
+
+#[inline(never)]
+fn cmp(a: usize, b: usize) -> bool {
+    a == b
+}
+
+#[inline(always)]
+fn cmp_in(a: usize, b: usize) -> bool {
+    a == b
+}
+
+fn main() {
+    let a = {
+        let v = 0;
+        addr_of!(v).expose_provenance()
+    };
+    let b = {
+        let v = 0;
+        addr_of!(v).expose_provenance()
+    };
+    assert_eq!(a.to_string(), b.to_string());
+    println!("{a:?} == {b:?} -> ==: {}, cmp_in: {}, cmp: {}", a == b, cmp_in(a, b), cmp(a, b));
+}

tests/ui/codegen/equal-pointers-unequal/exposed-provenance/inline2.run.stdout

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+<..> == <..> -> ==: true, cmp_in: true, cmp: true