[LLVMbugs] [Bug 12457] New: libstdc++4.7 requires various math builtins to be constant expressions

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12457

             Bug #: 12457
           Summary: libstdc++4.7 requires various math builtins to be
                    constant expressions
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++11
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: richard-llvm at metafoo.co.uk
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified


libstdc++4.7 declares a bunch of <cmath> functions as constexpr, defined as
calling __builtin_foo. This doesn't work: those builtins aren't treated as
potential constant expressions. Consequently we reject this code:

cmath:107:3: error: constexpr function never produces a constant expression
  acos(float __x)
  ^
cmath:108:12: note: non-constexpr function '__builtin_acosf' cannot be used in
a constant expression
  { return __builtin_acosf(__x); }
           ^
cmath:108:12: note: declared here

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