[LLVMbugs] [Bug 16056] New: std::atomic variables are never constant initialized

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16056

            Bug ID: 16056
           Summary: std::atomic variables are never constant initialized
           Product: clang
           Version: trunk
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: st at quanttec.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

static std::atomic<..> variables are not properly constant initialized. If you
look at the assembly generated by clang for the following test case, you'll see
that testVar2 is not constant initialized to -1 as it should be.

#include <atomic>
int testVar1{-1};
std::atomic<int> testVar2{-1};

The following test case seems to suggest that this might be a problem with the
built-in _Atomic types:

struct TestVar {
  _Atomic(int) value;

  constexpr TestVar(int value) : value(value) {}
};

TestVar testVar{-1};

test.cpp:5:13: error: constexpr constructor never produces a constant
expression [-Winvalid-constexpr]
  constexpr TestVar(int value) : value(value) {}
            ^
test.cpp:5:40: note: non-literal type '_Atomic(int)' cannot be used in a
constant expression
  constexpr TestVar(int value) : value(value) {}
                                       ^

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