[LLVMbugs] [Bug 13553] New: Different behavior between g++ and clang++ when evaluating function calls as parameters

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Wed Aug 8 12:45:51 PDT 2012


             Bug #: 13553
           Summary: Different behavior between g++ and clang++ when
                    evaluating function calls as parameters
           Product: clang
           Version: unspecified
          Platform: Macintosh
        OS/Version: MacOS X
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: wilbert at jdg.info
                CC: dgregor at apple.com, llvmbugs at cs.uiuc.edu
    Classification: Unclassified

When compiling the following code:

#include <iostream>

int Func1()
    std::cout << "In Func1" << std::endl;
    return 1;
int Func2()
    std::cout << "In Func2" << std::endl;
    return 2;

void FuncA(int a, int b)

int main(int argc, const char **argv)
    FuncA( Func1(), Func2() );
    return 0;

And building it with g++ and clang++:
> g++ test.cpp -o test-g++
> clang++ test.cpp -o test-clang++

And executing the builds then the actual output is different:
> ./test-g++ 
In Func2
In Func1
> ./test-clang++ 
In Func1
In Func2

I can imagine that this could lead to some really hard to track issues when
people are switching from gcc (or VS2010) ro clang.
I am also not sure how this is defined in the C/C++ specs.

The versions used (standard XCode 4.4 binaries):
> g++ --version
i686-apple-darwin11-llvm-g++-4.2 (GCC) 4.2.1 (Based on Apple Inc. build 5658)
(LLVM build 2336.11.00)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO

> clang++ --version
Apple clang version 4.0 (tags/Apple/clang-421.0.57) (based on LLVM 3.1svn)
Target: x86_64-apple-darwin12.0.0
Thread model: posix

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