LLVM assertion error when dereferencing "&mut Iterator<Item=Something>" from function parameter

[mottalli]

Offending code:

extern crate core;
use core::fmt;

fn show_all<I: fmt::String>(iter: &mut Iterator<Item=I>) {
    for i in *iter {
        println!("{}", i);
    }
}

fn main() {
    let v = vec![1i32, 2, 3, 4];
    show_all(&mut v.iter());
}

Compiler error (formatted):

rustc: /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/llvm/lib/IR/Instructions.cpp:281: 
void llvm::CallInst::init(llvm::Value*, llvm::ArrayRef<llvm::Value*>, const llvm::Twine&): 
Assertion `(i >= FTy->getNumParams() || FTy->getParamType(i) == Args[i]->getType()) && 
"Calling a function with a bad signature!"' failed.

Rust version:

$ rustc --version
rustc 1.0.0-nightly (f4f10dba2 2015-01-17 20:31:08 +0000)

[mottalli]

I compiled Rust from source and the previous error becomes this:

Call parameter type does not match function signature!
  %11 = load { i8*, void (i8*)** }* %__fat_ptr
 { i8*, void (i8*)** }*  %12 = call i8* @"_ZN216fn$LP$$BP$mut$u{20}core..iter..Iterator$u{20}$u{2b}$u{20}$u{27}static$RP$$u{20}.$GT$$u{20}core..option..Option$LT$$LT$core..iter..Iterator$u{20}$u{2b}$u{20}$u{27}static$u{20}as$u{20}core..iter..Iterator$GT$..Item$GT$16object_shim.166317h29bc7de23a846978E"({ i8*, void (i8*)** } noalias nocapture dereferenceable(16) %11)
LLVM ERROR: Broken function found, compilation aborted!

Rust version:

$ rustc --version
rustc 1.0.0-dev (dcaeb6aa2 2015-01-18 11:28:53 +0000)

[mottalli]

I found out that the problem is on the loop:

    for i in *iter {
        println!("{}", i);
    }

If I replace this with the expanded version of the loop:

    loop {
        match (*iter).next() {
            Some(ref i) => println!("{}", i),
            None => break
        }
    }

it compiles and works as expected. So, the problem seems to be that the compiler is unable to dereference the Iterator trait, maybe it has something to do with the fact that I am forcing Item to be of a specific type? (i.e. Iterator<Type=I>)

[theemathas]

Minimal code:

fn foo(it: &mut Iterator<Item = i32>) {
    for x in *it {}
}

fn main() { }

playpen

The ICE:

rustc: /build/rust-git/src/rust/src/llvm/lib/IR/Instructions.cpp:281: void llvm::CallInst::init(llvm::Value*, llvm::ArrayRef<llvm::Value*>, const llvm::Twine&): Assertion `(i >= FTy->getNumParams() || FTy->getParamType(i) == Args[i]->getType()) && "Calling a function with a bad signature!"' failed.

Removing the associated type results in a variant of #21137

[nikomatsakis]

Gah, I feel like I've fixed this bug once before.

[japaric]

Duplicate of #20605

To avoid the LLVM assertion, don't dereference the iterator in the for loop. This doesn't crash:

fn foo(it: &mut Iterator<Item = i32>) {
    for x in it {}
//~^ error: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
}

fn main() { }

Instead, you get a compiler error, I think that compiler error maybe be a different bug.

[japaric]

I filled issue #21655 for the for _ in ref_mut_trait_object {} bug.