[llvm-bugs] [Bug 24608] New: undefined behaviour of nested anonymous unions with bitfields doesn't work as intended

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=24608

            Bug ID: 24608
           Summary: undefined behaviour of nested anonymous unions with
                    bitfields doesn't work as intended
           Product: clang
           Version: 3.6
          Hardware: Sun
                OS: Solaris
            Status: NEW
          Severity: normal
          Priority: P
         Component: LLVM Codegen
          Assignee: unassignedclangbugs at nondot.org
          Reporter: stefan.teleman at oracle.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

This is a placeholder bug for a patch I will be submitting very shortly.

in ${top_srcdir}/tools/clang/include/clang/lib/AST/TemplateBase.h:

class TemplateArgument makes uses of an anonymous union of several structs.
One of these structs, namely struct I, contains an union of bitfields. Also,
class TemplateArgument does not explicitly define a copy constructor and an
assignment operator, it relies on the compiler-generated defaults.

C++ bitfields inside an union are undefined behaviour according to the
Standard. Relying on compiler default-generated copy-constructor and
assignment operator for copying unions with bitfields of different type,
or size, is undefined behaviour as well.

This happens to work correctly on Intel (i386/x86_64) but does not work at
all on SPARC.

I have a patch for this defect, which corrects it. I will submit this patch
very shortly.

We have a number of clang and llvm patches for Solaris, and we have every
intention of contributing them to the project. This is just one of several
bugs with follow-up patches that I will be filing.

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