[Bug c++/67468] New: compiler changes template argument

[cas43 at cs dot stanford.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67468

            Bug ID: 67468
           Summary: compiler changes template argument
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cas43 at cs dot stanford.edu
  Target Milestone: ---

When compiled with:

g++ -c prog.cpp -Q

The compiler output contains "B<A<S>::x>" but the input contains "B<A<R>::x>". 
The compiler has replaced the template argument R with the template argument S.

CODE:

template<class T> struct A
{
    const static int x=0;
};
template<int d> struct B;
template<class R,class S> class C
{
    const static int x=A<R>::x<A<S>::x?A<R>::x:A<S>::x;
};
template<class T,class R,class S> int Get_Block_At_Mask(const C<R,S>&
c,B<A<R>::x>* b)
{
    return 0;
}

COMPILER OUTPUT:

 int Get_Block_At_Mask(const C<R, S>&, B<A<S>::x>*)
Analyzing compilation unit
Performing interprocedural optimizations
 <*free_lang_data> <visibility> <build_ssa_passes> <opt_local_passes>
<free-inline-summary> <whole-program> <inline>Assembling functions:

Execution times (seconds)
 phase setup             :   0.00 ( 0%) usr   0.00 ( 0%) sys   0.01 (100%) wall
   1381 kB (80%) ggc
 TOTAL                 :   0.00             0.00             0.01              
1734 kB
Extra diagnostic checks enabled; compiler may run slowly.
Configure with --enable-checking=release to disable checks.

COMPILER VERSIONS TESTED:

Using built-in specs.
COLLECT_GCC=/home/craig/new-gcc/i-trunk/bin/g++
COLLECT_LTO_WRAPPER=/home/craig/new-gcc/i-trunk/libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../s-trunk/configure --prefix=/home/craig/new-gcc/i-trunk
Thread model: posix
gcc version 6.0.0 20150906 (experimental) (GCC) 

-- and --

g++-5 (Ubuntu 5.1.0-0ubuntu11~14.04.1) 5.1.0
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