[Bug c++/53900] New: Too optimistic on a alignment assert

[gael.guennebaud at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53900

             Bug #: 53900
           Summary: Too optimistic on a alignment assert
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: gael.guenneb...@gmail.com


Created attachment 27766
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27766
an example triggering the issue.

Since gcc 4.7 the assertion of the attached piece of code is resolved at
compile-time while there is no guaranty, for instance when using a non-aligned
memory allocator, or on some systems where function arguments cannot be
aligned.

Here is the output with gcc-4.7:

$ g++-4.7 -m32 alignedassert.cpp && ./a.out
0x8321008
0x832100c

no assertion!

And with gcc 4.6:

$ g++-4.6 -m32 alignedassert.cpp && ./a.out
0x9322008
a.out: alignedassert.cpp:12: Foo::Foo(): Assertion `(std::ptrdiff_t(array) &
std::ptrdiff_t(0xf))==0' failed.
Aborted


Or without the -m32 flag:

$ g++-4.7 alignedassert.cpp && ./a.out
0xde3010
0xde3014

$ g++-4.6 alignedassert.cpp && ./a.out
0x1f03010
0x1f03014
a.out: alignedassert.cpp:12: Foo::Foo(): Assertion `(std::ptrdiff_t(array) &
std::ptrdiff_t(0xf))==0' failed.
Aborted