LLVM doesn't understand Some(Box<u32>) is always some

[playground](https://play.rust-lang.org/?gist=4eafc9285fd5d642c94e1e92f5b6f7d1&version=nightly&mode=release)

For the following code:

``` rust
use std::mem;

fn foo<T>(a: &mut T, b: T) -> bool {
    let b = Some(mem::replace(a, b));
    let ret = b.is_some();
    mem::forget(b);
    return ret
}

pub fn foo_u32(a: &mut u32, b: u32) -> bool {
    foo(a, b)
}

pub fn foo_box(a: &mut Box<u32>, b: Box<u32>) -> bool {
    foo(a, b)
}
```

This compiles down to the IR (optimized)

``` ll
; Function Attrs: norecurse uwtable
define zeroext i1 @_ZN3foo7foo_u3217h93ddaaeb1c2cc2b2E(i32* nocapture dereferenceable(4), i32) unnamed_addr #0  {
entry-block:
  store i32 %1, i32* %0, align 4
  ret i1 true
}

; Function Attrs: norecurse uwtable
define zeroext i1 @_ZN3foo7foo_box17hd05578023690d1faE(i32** nocapture dereferenceable(8), i32* noalias dereferenceable(4)) unnamed_addr #0  {
entry-block:
  %2 = ptrtoint i32* %1 to i64
  %3 = bitcast i32** %0 to i64*
  %4 = bitcast i32** %0 to i8**
  %5 = load i8*, i8** %4, align 8, !noalias !0
  store i64 %2, i64* %3, align 8, !noalias !0
  %not.switchtmp.i.i = icmp ne i8* %5, null
  ret i1 %not.switchtmp.i.i
}

attributes #0 = { norecurse uwtable }
attributes #1 = { nounwind }
```

It seems odd that the `Box` case is not as optimized as the `u32` case? This seems due to the null-pointer optimization of the `Option<Box>` itself. I wonder if there's more metadata we can attach to tell LLVM the loads aren't null?


Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

LLVM doesn't understand Some(Box<u32>) is always some #36010

Metadata

Assignees

Labels

Type

Fields

Projects

Milestone

Relationships

Development

Uh oh!

LLVM doesn't understand Some(Box<u32>) is always some #36010

Description

Metadata

Metadata

Assignees

Labels

Type

Fields

Projects

Milestone

Relationships

Development

Issue actions