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From: "ai.azuma at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/53401] New: internal compiler error: Segmentation fault on infinite argument deduction of constexpr templates
Date: Fri, 18 May 2012 17:31:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53401

             Bug #: 53401
           Summary: internal compiler error: Segmentation fault on
                    infinite argument deduction of constexpr templates
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: ai.azuma@gmail.com


Created attachment 27434
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27434
Outputs from -v option (repeated error messages are snipped) and preprocessed
source.

The following invalid code causes an ICE with GCC 4.8.0 20120513 (experimental)
and -std=c++11.


/////////////////////////////////////////////
template<int I>
struct index
{};

constexpr int recursive_impl(index<0u>)
{
  return 0;
}

template<int N>
constexpr auto recursive_impl(index<N>)       // Line 11
  -> decltype(recursive_impl(index<N - 1>()))
{
  return recursive_impl(index<N - 1>());
}

template<int N>
constexpr auto recursive()
  -> decltype(recursive_impl(index<N>()))
{
  return recursive_impl(index<N>());
}

void f(int i)
{
  recursive<1>();
}
/////////////////////////////////////////////

g++: internal compiler error: Segmentation fault (program cc1plus)
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.


The above-mentioned code is invalid because there isn't anything to prevent the
compiler from trying infinite template argument deduction in the second
overload of `recursive_impl' (Line 11). So, I expect error messages like
"template instantiation depth exceeds maximum...". However, the compiler dies
in segmentation fault.

`constexpr' is necessary to reproduce the ICE. Otherwise, the compiler outputs
ordinary error messages as expected.

4.6.4 20120511 (prerelease) and 4.7.1 20120512 (prerelease) also cause the same
problem, too.