[LLVMbugs] [Bug 19741] New: clang incorrectly rejects constexpr constructor which modified member variable in its body

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=19741

            Bug ID: 19741
           Summary: clang incorrectly rejects constexpr constructor which
                    modified member variable in its body
           Product: clang
           Version: 3.4
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++1y
          Assignee: unassignedclangbugs at nondot.org
          Reporter: ytj000 at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

struct A {
        int a = 0;
        constexpr A() { a = 1; }
    };

    constexpr bool f() {
        constexpr A a;
        static_assert(a.a == 1, ""); // L1: OK
        return a.a == 1;
    }
    static_assert(f(), ""); // L2: Error, can not modify A::a in constexpr

- Online Compiler URL: http://goo.gl/jni6Em
- Compiler: clang 3.4 (with -std=c++1y)
- System: Linux 3.2


The constructor satisfies all the conditions listed in §7.1.5/4 of N3936.
However, clang complains:

clang++ -stdlib=libc++ -std=c++1y a.cpp -c -o a.o -Wall
a.cpp:11:15: error: static_assert expression is not an integral constant
expression
static_assert(f(), ""); // L2: Error
              ^~~
a.cpp:3:23: note: modification of object of const-qualified type 'const int' is
not allowed in a constant expression
    constexpr A() { a = 1; }
                      ^
a.cpp:7:17: note: in call to 'A()'
    constexpr A a;
                ^
a.cpp:11:15: note: in call to 'f()'
static_assert(f(), ""); // L2: Error
              ^
1 error generated.

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