rust/src/test/codegen/non-terminate/infinite-loop-1.rs

// compile-flags: -C opt-level=3 -Z insert-sideeffect

#![crate_type = "lib"]

fn infinite_loop() -> u8 {
    loop {}
}

// CHECK-LABEL: @test
#[no_mangle]
fn test() -> u8 {
    // CHECK-NOT: unreachable
    // CHECK: br label %{{.+}}
    // CHECK-NOT: unreachable
    let x = infinite_loop();
    x
}
Gate llvm.sideeffect under -Z insert-sideeffect 2019-09-27 23:13:53 +00:00			`// compile-flags: -C opt-level=3 -Z insert-sideeffect`
Add llvm.sideeffect to potential infinite loops and recursions LLVM assumes that a thread will eventually cause side effect. This is not true in Rust if a loop or recursion does nothing in its body, causing undefined behavior even in common cases like `loop {}`. Inserting llvm.sideeffect fixes the undefined behavior. As a micro-optimization, only insert llvm.sideeffect when jumping back in blocks or calling a function. A patch for LLVM is expected to allow empty non-terminate code by default and fix this issue from LLVM side. https://github.com/rust-lang/rust/issues/28728 2019-06-06 00:39:20 +00:00
			`#![crate_type = "lib"]`

			`fn infinite_loop() -> u8 {`
			`loop {}`
			`}`

			`// CHECK-LABEL: @test`
			`#[no_mangle]`
			`fn test() -> u8 {`
			`// CHECK-NOT: unreachable`
			`// CHECK: br label %{{.+}}`
			`// CHECK-NOT: unreachable`
			`let x = infinite_loop();`
			`x`
			`}`