[llvm-bugs] [Bug 36651] New: Undefined behavior in SmallVector implementation

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=36651

            Bug ID: 36651
           Summary: Undefined behavior in SmallVector implementation
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Core LLVM classes
          Assignee: unassignedbugs at nondot.org
          Reporter: tstellar at redhat.com
                CC: llvm-bugs at lists.llvm.org

Compiling with gcc 8 gives lots of warnings like:

/builddir/build/BUILD/llvm-6.0.0rc2.src/include/llvm/ADT/SmallVector.h:299:13:
warning: 'void* memcpy(void*, const void*, size_t)' writing to an object of
type 'struct std::pair<const llvm::MCSymbol*, const llvm::MCSymbol*>' with no
trivial copy-assignment; use copy-assignment or copy-initialization instead
[-Wclass-memaccess]
       memcpy(Dest, I, (E - I) * sizeof(T));


This is undefined behavior, which can be fixed by using:
std::uninitialized_copy(), or maybe more optimally by first checking if T is
trivially copy-able.  However, this code is only supposed to be called on POD
types, so there may be a bug somewhere else that is causing non-POD types to go
down this path.

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