[LLVMbugs] [Bug 23276] New: Template version of std::pow fails to compile

[bugzilla-daemon at llvm.org]

https://llvm.org/bugs/show_bug.cgi?id=23276

            Bug ID: 23276
           Summary: Template version of std::pow fails to compile
           Product: libc++
           Version: unspecified
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: programmdude at gmail.com
                CC: llvmbugs at cs.uiuc.edu, mclow.lists at gmail.com
    Classification: Unclassified

I came up with a compile error when using emscripten 1.30 on windows, which
uses libcxx as it's c++ library.
When I peeked into the headers to find out what exactly caused it, I determined
that this static assert was causing it to fail, the relevant lines are below.

typedef typename __promote<_A1, _A2>::type __result_type;
static_assert((!(is_same<_A1, __result_type>::value && is_same<_A2,
__result_type>::value)), "");

Essentially, the two is_same queries are being inverted, so if both are true
then false is being passed to static_assert. According to MSDN, static_assert
fails if it's false. Unless I am mistaken, it should work correctly without the
invert operator.

For reference, compiling with std::pow<float>(1.0f, 2.0f) was able to get this
error.

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