Symbol names for generics are not stable across crates

[dotdash]

Given this:
cgu.rs

#![crate_type="lib"]
pub fn id<T>(t: T) -> T {
  t
}
pub fn user() {
  id(0);
}

a.rs

#![crate_type="lib"]
extern crate cgu;
pub fn user() {
  cgu::id(0);
}

We get two different symbol names for the monomorphizations of id.

cgu.ll

define internal i32 @_ZN3cgu2id17h7cbc0f1ce1830012E(i32) unnamed_addr #0 {
entry-block:
  %dropflag_hint_6 = alloca i8
  %t = alloca i32
  store i8 61, i8* %dropflag_hint_6
  store i32 %0, i32* %t
  %1 = load i32, i32* %t
  ret i32 %1
}

a.ll

define internal i32 @_ZN3cgu2id17h8a873a51d5137f87E(i32) unnamed_addr #0 {
entry-block:
  %t = alloca i32
  store i32 %0, i32* %t
  %1 = load i32, i32* %t
  ret i32 %1
}

cc @nikomatsakis @michaelwoerister

[michaelwoerister]

Interesting.

[michaelwoerister]

I'm going to look into this a little...

[michaelwoerister]

That might be the culprit:

rust/src/librustc/ty/context.rs

Line 437 in 641204a

self.sess.cstore.crate_name(cnum)

pub fn crate_disambiguator(&self, cnum: ast::CrateNum) -> token::InternedString {
        if cnum == LOCAL_CRATE {
            self.sess.crate_disambiguator.get().as_str()
        } else {
            self.sess.cstore.crate_name(cnum)
        }
    }

One at least...

[nikomatsakis]

@michaelwoerister d'oh that looks like a copy-n-paste bug...

On Tue, Mar 29, 2016 at 10:46 AM, Michael Woerister <
notifications@github.com> wrote:

That might be the culprit:

rust/src/librustc/ty/context.rs

Line 437 in 641204a

self.sess.cstore.crate_name(cnum)

pub fn crate_disambiguator(&self, cnum: ast::CrateNum) -> token::InternedString {
if cnum == LOCAL_CRATE {
self.sess.crate_disambiguator.get().as_str()
} else {
self.sess.cstore.crate_name(cnum)
}
}

One at least...

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#32554 (comment)

[michaelwoerister]

It does. I'm currently in the process of writing a test case for this.

[arielb1]

aren't these internal symbols anyway?

[dotdash]

@arielb1 Not necessarily when using multiple codegen units. And even otherwise, it's nice to have the same name across all crates. In theory, for a size-optimized build we might also want to switch to linkonce_odr or weak_odr linkage, in which case we'd also need the names to be the same.