[LLVMbugs] [Bug 9999] New: A simple recursive TMP static const initializer defeats clang.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=9999

           Summary: A simple recursive TMP static const initializer
                    defeats clang.
           Product: clang
           Version: 2.8
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: phorgan1 at gmail.com
                CC: llvmbugs at cs.uiuc.edu, dgregor at apple.com


Created an attachment (id=6635)
 --> (http://llvm.org/bugs/attachment.cgi?id=6635)
Test program to illustrate the problem built with clang -c testit.cpp

clang version 2.8 (branches/release_28)
Target: i386-pc-linux-gnu
Thread model: posix

This works on gcc but not on clang:

template<unsigned int v>
class bitWidthHolding {
public:
    /** width is the number of bits occupied by the template parameter v
        */
    static const
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
};

static const int width=bitWidthHolding<255>::width;

Error is: 
patrick at dell$ clang -c testit.cpp
testit.cpp:7:67: error: in-class initializer is not an integral constant
      expression
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~
testit.cpp:7:40: note: in instantiation of template class 'bitWidthHolding<0>'
      requested here
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                                       ^
testit.cpp:7:40: note: in instantiation of template class 'bitWidthHolding<1>'
      requested here
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                                       ^
testit.cpp:7:40: note: in instantiation of template class 'bitWidthHolding<3>'
      requested here
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                                       ^
testit.cpp:7:40: note: in instantiation of template class 'bitWidthHolding<7>'
      requested here
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                                       ^
testit.cpp:7:40: note: in instantiation of template class 'bitWidthHolding<15>'
      requested here
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                                       ^
testit.cpp:7:40: note: in instantiation of template class 'bitWidthHolding<31>'
      requested here
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                                       ^
testit.cpp:7:40: note: in instantiation of template class 'bitWidthHolding<63>'
      requested here
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                                       ^
testit.cpp:7:40: note: in instantiation of template class
'bitWidthHolding<127>'
      requested here
    unsigned int width = (v == 0 ? 0 : bitWidthHolding<(v >> 1)>::width + 1);
                                       ^
testit.cpp:10:24: note: in instantiation of template class
      'bitWidthHolding<255>' requested here
static const int width=bitWidthHolding<255>::width;
                       ^
1 error generated.

The real error is the top one, which should be static const int 0, and is not
recognized as const.  For us it's a showstopper, we can't use clang because of
this.

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