[cfe-dev] Inconsistent mangling of C++ unnamed types compiling source code vs compiling AST files

[Tom Honermann]

Thank you!  Funny, I was just about to submit my own patch when I got 
your email.  Your patch is better :)

I verified this resolved the problem (and also back ported the change to 
Clang 3.4 where it worked fine as well).

Tom.

On 03/20/2014 09:55 PM, Richard Smith wrote:
> Thanks for the report, should be fixed in r204423.
>
>
> On Tue, Mar 18, 2014 at 9:33 PM, Tom Honermann <thonermann at coverity.com
> <mailto:thonermann at coverity.com>> wrote:
>
>     According to the Itanium C++ ABI, The unnamed structures nested in
>     struct S below should be assigned the names 'N1SUt_' and 'N1SUt0_'
>     respectively.  And indeed, Clang versions 3.3 and newer do assign
>     these names when compiling the source directly.  However, when the
>     source is first emitted to a .ast file and then compiled, both of
>     the unnamed structures are assigned the same mangled name
>     (presumably because mangling discriminators are not being preserved
>     in the .ast file).  For the test case below, this results in both
>     instantiations of the tf() template function receiving the same name
>     and one being discarded.
>
>     I tested this behavior with Clang versions 3.3 through trunk (pulled
>     tonight).  Clang 3.2 produces consistent behavior, though the names
>     generated in that release don't conform to the Itanium ABI.
>
>     Warnings regarding the use of an unnamed type as a template argument
>     are issued when compiling the test case below.  This test case was
>     contrived to demonstrate that both unnamed types are being assigned
>     the same name.
>
>     $ cat t.cpp
>     struct S {
>        struct {
>          int i;
>        } s1;
>        struct {
>          int i;
>        } s2;
>     } s;
>
>     template<typename T>
>     void tf(T t) {}
>
>     void f() {
>        tf(s.s1);
>        tf(s.s2);
>     }
>
>     $ clang -c t.cpp
>     ...
>
>     $ nm t.o
>     0000000000000000 T _Z1fv
>     0000000000000000 W _Z2tfIN1SUt0_EEvT_
>     0000000000000000 W _Z2tfIN1SUt_EEvT_
>     0000000000000000 B s
>
>     $ clang -emit-ast t.cpp
>     ...
>
>     $ clang -c t.ast
>
>     $ nm t.o
>     0000000000000000 T _Z1fv
>     0000000000000000 W _Z2tfIN1SUt_EEvT_
>     0000000000000000 B s
>
>     Tom.
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