Auto merge of rust-lang#127003 - GrigorenkoPV:107975, r=SparrowLii

Add a test for rust-lang#107975

The int is zero. But also not zero. This is so much fun.

This is a part of rust-lang#105107.

Initially I was going to just rebase rust-lang#108445, but quite a few things changed since then:
* The [mcve](rust-lang#105787 (comment)) used for rust-lang#105787 got fixed.[^upd2]
* You can't just `a ?= b` for rust-lang#107975 anymore. Now you have to `a-b ?= 0`. This is what this PR does. As an additional flex, it show that three ways of converting a pointer to its address have this issue:
  1. `as usize`
  2. `.expose_provenance()`
  3. `.addr()`
* rust-lang#108425 simply got fixed. Yay.

As an aside, the naming for `addr_of!` is quite unfortunate in context of provenance APIs. Because `addr_of!` gives you a pointer, but what provenance APIs refer to as "address" is the `usize` value. Oh well.

UPD1: GitHub is incapable of parsing rust-lang#107975 in the PR name, so let's add it here.

[^upd2]: UPD2: [The other mcve](rust-lang#105787 (comment)) does not work anymore either, saying "this behavior recently changed as a result of a bug fix; see rust-lang#56105 for details."

Author: bors

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

@@ -0,0 +1,22 @@
+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
+//@ compile-flags: -Copt-level=2
+//@ 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
+//@ compile-flags: -Copt-level=2
+//@ 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
+//@ compile-flags: -Copt-level=2
+//@ 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
+//@ compile-flags: -Copt-level=2
+//@ 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
+//@ compile-flags: -Copt-level=2
+//@ 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
+//@ compile-flags: -Copt-level=2
+//@ 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
+}