src/test/codegen/dst-vtable-align-nonzero.rs

// compile-flags: -O

#![crate_type = "lib"]

// This test checks that we annotate alignment loads from vtables with nonzero range metadata,
// and that this allows LLVM to eliminate redundant `align >= 1` checks.

pub trait Trait {
    fn f(&self);
}

pub struct WrapperWithAlign1<T: ?Sized> { x: u8, y: T }

pub struct WrapperWithAlign2<T: ?Sized> { x: u16, y: T }

pub struct Struct<W: ?Sized> {
    _field: i8,
    dst: W,
}

// CHECK-LABEL: @eliminates_runtime_check_when_align_1
#[no_mangle]
pub fn eliminates_runtime_check_when_align_1(
    x: &Struct<WrapperWithAlign1<dyn Trait>>
) -> &WrapperWithAlign1<dyn Trait> {
    // CHECK: load [[USIZE:i[0-9]+]], {{.+}} !range [[RANGE_META:![0-9]+]]
    // CHECK-NOT: llvm.umax
    // CHECK-NOT: icmp
    // CHECK-NOT: select
    // CHECK: ret
    &x.dst
}

// CHECK-LABEL: @does_not_eliminate_runtime_check_when_align_2
#[no_mangle]
pub fn does_not_eliminate_runtime_check_when_align_2(
    x: &Struct<WrapperWithAlign2<dyn Trait>>
) -> &WrapperWithAlign2<dyn Trait> {
    // CHECK: [[X0:%[0-9]+]] = load [[USIZE]], {{.+}} !range [[RANGE_META]]
    // CHECK: {{icmp|llvm.umax}}
    // CHECK: ret
    &x.dst
}

// CHECK: [[RANGE_META]] = !{[[USIZE]] 1, [[USIZE]] 0}