Comparison of static arrays

[ghost]

Hello,

Just posting this to see if it is a bug. The expected behaviour would be that test==test1, therefore 'true' would be printed, however the below prints false. This was tested on windows running 0.6 release.

struct signature<'self> {   
  pattern   : &'self [u32] 
}

static test1: signature<'static> =  signature {
  pattern: &[0x243f6a88u32,0x85a308d3u32,0x13198a2eu32,0x03707344u32,0xa4093822u32,0x299f31d0u32]
};

fn main() {
  let test = &[0x243f6a88u32,0x85a308d3u32,0x13198a2eu32,0x03707344u32,0xa4093822u32,0x299f31d0u32];
  println(fmt!("%b",test==test1.pattern));

}

Edit: changed code, made sure types are correct, retested, returns false on 0.6

[Blei]

This doesn't compile on incoming. Especially the types don't match, test1 should actually a u32 array. After making it compile, it prints true.

[ghost]

@Blei Hi Blei, my bad, I have fixed the code, could you please confirm this works on incomming? If it is fixed in incomming I will close.

[Blei]

Hmm, this prints false even on incoming. Definitely a bug.

[Aatch]

As some more information, I did some more checking, and this is almost certainly a bug in codegen.

If you make the comparison a function, marked no-inline, then LLVM compresses it down to a single ret 0 instruction after optimization, so whatever we generate is wrong. Unfortunately there is a lot of IR without optimizations, I don't have the motivation to pour through ~2000 lines of code trying to find the error.

I'm also nominating this.

[dotdash]

The length is incorrectly set for vector slices in fields in static structs.

struct signature<'self> {
    pattern   : &'self [u32] 
}

struct signature2<'self> {
    pattern   : &'self str,
}

static test1: signature<'static> =  signature {
    pattern:   &[0x243f6a88u32,0x85a308d3u32,0x13198a2eu32,0x03707344u32,0xa4093822u32,0x299f31d0u32],
};
static test2: signature2<'static> =  signature2 {
    pattern:   "Hello!",
};

static test3: &'static [u32] = &[0x243f6a88u32,0x85a308d3u32,0x13198a2eu32,0x03707344u32,0xa4093822u32,0x299f31d0u32];

fn main() {
    println(fmt!("Static &[u32] field:\t%2u", test1.pattern.len()));
    println(fmt!("Static &str field:\t%2u", test2.pattern.len()));
    println(fmt!("Static &[u32]:\t\t%2u", test3.len()));
}

Results in

Static &[u32] field:     4
Static &str field:       6
Static &[u32]:           6

Corresponding llvm code:

@const = private constant [6 x i32] [i32 608135816, i32 -2052912941, i32 320440878, i32 57701188, i32 -1542899678, i32 698298832]
@const1 = private constant { i32*, i64 } { i32* getelementptr inbounds ([6 x i32]* @const, i32 0, i32 0), i64 24 }
@_ZN5test116_69389145026f68d3_00E = internal constant { { { i32*, i64 }*, i64 } } { { { i32*, i64 }*, i64 } { { i32*, i64 }* @const1, i64 16 } }
@str2900 = internal constant [7 x i8] c"Hello!\00"
@_ZN5test217_86eff3e34b82f2c13_00E = internal constant { { i8*, i64 } } { { i8*, i64 } { i8* getelementptr inbounds ([7 x i8]* @str2900, i32 0, i32 0), i64 7 } }
@const2 = private constant [6 x i32] [i32 608135816, i32 -2052912941, i32 320440878, i32 57701188, i32 -1542899678, i32 698298832]
@_ZN5test314_8a97a17587e323_00E = internal constant { i32*, i64 } { i32* getelementptr inbounds ([6 x i32]* @const2, i32 0, i32 0), i64 24 }

[Aatch]

Between the two of us, me and @dotdash have isolated this down to an auto-borrowing bug.

Basically for this:

static test : Foo<'static> = Foo {
    field: &'static [1,2,3]
};

The [1,2,3] part of the expression is auto-borrowed, then the &'static part causes it to slice. So, it actually constructs a &'static &'static [uint], in terms of the code gen.

One workaround (that will likely break when this is fixed) is to do this:

static test : Foo<'static> = Foo {
    field: [1,2,3]
}

as the vector expression is still auto-borrowed.

I ran up against my understanding of the compiler internals, but I narrowed it down to some wrong logic concerning the adjustments table. What, where or when this happens is beyond my knowledge, unfortunately.

[huonw]

This seems similar to #5688.

[mstewartgallus]

Unfortunately, this workaround isn't good enough for my purposes because it can not be uniformly applied. See the following example for details.

struct Foo(&'static [&'static [uint]]);

static works: Foo = Foo([&'static [0, 1, 2, 3]]);
// static fails: Foo = Foo([[0, 1, 2, 3]]);

fn main() {
}

[alexcrichton]

The code example in the original issue now works, flagging as needstest