clang gets confused with alias and asm labels

[llvmbot]

Bugzilla Link	9177
Resolution	FIXED
Resolved on	Feb 15, 2011 19:41
Version	trunk
OS	All
Reporter	LLVM Bugzilla Contributor

Extended Description

Given

---

int attribute((visibility("hidden"))) foo (void);
extern __typeof (foo) foo asm ("INT_foo") attribute((visibility("hidden"))) ;
int foo (void) {
}
extern __typeof (foo) EXT_foo asm("foo") attribute((alias("INT_foo")));

Clang will produce

---

@"\01foo" = alias i32 ()* @​INT_foo
define hidden i32 @"\01INT_foo"() nounwind {
entry:
%retval = alloca i32, align 4
%0 = load i32* %retval
ret i32 %0
}
declare i32 @​INT_foo()

Note how we have a declaration for INT_foo and a definition for "\01INT_foo". This gets resolved by LLVM's codegen, but causes problems to LTO because the alias foo is pointing to a declaration.

Producing

@"\01foo" = alias i32 ()* @"\01INT_foo"
define hidden i32 @"\01INT_foo"() nounwind {
entry:
%retval = alloca i32, align 4
%0 = load i32* %retval
ret i32 %0
}

would fix the problem.

[llvmbot]

A possible workaround is to write

int attribute((visibility("hidden"))) INT_foo (void);
extern __typeof (INT_foo) INT_foo attribute((visibility("hidden"))) ;
int INT_foo (void) {
}
extern __typeof (INT_foo) foo attribute((alias("INT_foo")));

The disadvantage is that the code then has to explicitly use "INT_foo()" instead of just "foo()".

[llvmbot]

llvm-gcc produces:

@"\01foo" = alias i32 ()* @"\01INT_foo"

define hidden i32 @"\01INT_foo"() nounwind readnone optsize {
entry:
ret i32 undef
}

I think it might be possible to replicate its hack. Will take a look.

[llvmbot]

hack for this case
The attached hack is similar (but more local) to the one in llvm-gcc. I would propose checking it in for now if it was the last thing blocking us doing LTO of firefox, but with this in I am now hitting what looks like a gold bug.

Will update this bug once that is fixed.

[llvmbot]

Turns out that was not sufficient. The problem is that it is possible for one file o have a definition for '\01foo' and another file a use of 'foo'.

We really have to be consistent across files. I am testing another hack.

[llvmbot]

Fixed by avoiding the \01 prefix when possible. d62acb5