*** Bug llvm/llvm-bugzilla-archive#9555 has been marked as a duplicate of this bug. ***

As of r158931, clang's error messages are better:

$ cat tmp.cc
class A;
void f0(A *a);
void f1(A &a);
void f2(A *a) {
f1(a);
}
void f3(A &a) {
f0(a);
}

$ ./bin/clang -fsyntax-only tmp.cc
tmp.cc:5:3: error: no matching function for call to 'f1'
f1(a);
^~
tmp.cc:3:6: note: candidate function not viable: cannot convert argument of incomplete type 'A *' to
'A &'
void f1(A &a);
^
tmp.cc:8:3: error: no matching function for call to 'f0'
f0(a);
^~
tmp.cc:2:6: note: candidate function not viable: cannot convert argument of incomplete type 'A' to
'A *'
void f0(A *a);
^
2 errors generated.

And if you change "class A;" to "class A {};":

$ ./bin/clang -fsyntax-only tmp.cc
tmp.cc:5:3: error: no matching function for call to 'f1'
f1(a);
^~
tmp.cc:3:6: note: candidate function not viable: no known conversion from 'A *' to 'A &' for 1st
argument; dereference the argument with *
void f1(A &a);
^
tmp.cc:8:3: error: no matching function for call to 'f0'
f0(a);
^~
tmp.cc:2:6: note: candidate function not viable: no known conversion from 'A' to 'A *' for 1st
argument; take the address of the argument with &
void f0(A *a);
^
2 errors generated.

The error message when A is an incomplete type could use a bit more love to make it more helpful like when A is a complete type, and there aren't any fix-it hints for any of the cases.

Created a patch submission here: http://reviews.llvm.org/D16949

mentioned in issue llvm/llvm-bugzilla-archive#9555

Linked patch was committed

@llvm/issue-subscribers-clang-codegen