[LLVMbugs] [Bug 12758] New: miscompilation of calls to __attribute__((pure)) virtual functions

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon May 7 14:51:46 PDT 2012


             Bug #: 12758
           Summary: miscompilation of calls to __attribute__((pure))
                    virtual functions
           Product: clang
           Version: unspecified
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: richard-llvm at metafoo.co.uk
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Consider this code:

struct B { virtual void f() __attribute__((pure)); };
struct D : B { void f(); };
void f(B *p) { p->f(); }
void g() { D b; f(&b); }

Here, B::f() is __attribute__((pure)), but D::f() is not. g++ emits a virtual
call within ::f(), but Clang does not. Likewise, g++ emits a call to D::f()
within ::g(), but Clang does not.

The GCC docs don't explicitly state what should happen here, but they do say
that 'pure' is a property of the function itself, which suggests that g++ is
right and clang is wrong.

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