[rustc.git] / tests / mir-opt / copy-prop / mutate_through_pointer.rs

// unit-test: CopyProp
//
// This attempts to mutate `a` via a pointer derived from `addr_of!(a)`. That is UB
// according to Miri. However, the decision to make this UB - and to allow
// rustc to rely on that fact for the purpose of optimizations - has not been
// finalized.
//
// As such, we include this test to ensure that copy prop does not rely on that
// fact. Specifically, if `addr_of!(a)` could not be used to modify a, it would
// be correct for CopyProp to replace all occurrences of `a` with `c` - but that
// would cause `f(true)` to output `false` instead of `true`.

#![feature(custom_mir, core_intrinsics)]
#![allow(unused_assignments)]
extern crate core;
use core::intrinsics::mir::*;

#[custom_mir(dialect = "analysis", phase = "post-cleanup")]
fn f(c: bool) -> bool {
    mir!({
        let a = c;
        let p = core::ptr::addr_of!(a);
        let p2 = core::ptr::addr_of_mut!(*p);
        *p2 = false;
        RET = c;
        Return()
    })
}

fn main() {
    assert_eq!(true, f(true));
}

// EMIT_MIR mutate_through_pointer.f.CopyProp.diff
Commit	Line	Data
add651ee FG	1	// unit-test: CopyProp
add651ee FG	2	//
9ffffee4 FG	3	// This attempts to mutate `a` via a pointer derived from `addr_of!(a)`. That is UB
	4	// according to Miri. However, the decision to make this UB - and to allow
	5	// rustc to rely on that fact for the purpose of optimizations - has not been
	6	// finalized.
	7	//
	8	// As such, we include this test to ensure that copy prop does not rely on that
	9	// fact. Specifically, if `addr_of!(a)` could not be used to modify a, it would
	10	// be correct for CopyProp to replace all occurrences of `a` with `c` - but that
	11	// would cause `f(true)` to output `false` instead of `true`.
	12
	13	#![feature(custom_mir, core_intrinsics)]
	14	#![allow(unused_assignments)]
	15	extern crate core;
	16	use core::intrinsics::mir::*;
	17
	18	#[custom_mir(dialect = "analysis", phase = "post-cleanup")]
	19	fn f(c: bool) -> bool {
	20	mir!({
	21	let a = c;
	22	let p = core::ptr::addr_of!(a);
	23	let p2 = core::ptr::addr_of_mut!(*p);
	24	*p2 = false;
	25	RET = c;
	26	Return()
	27	})
	28	}
	29
	30	fn main() {
	31	assert_eq!(true, f(true));
	32	}
	33
	34	// EMIT_MIR mutate_through_pointer.f.CopyProp.diff