[Bug c++/60124] New: g++ generates two copies of the same symbol due to __builtin_bswap32 return type

[mat at lcs dot mit.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60124

Bug ID: 60124
   Summary: g++ generates two copies of the same symbol due to
__builtin_bswap32 return type
   Product: gcc
   Version: 4.8.2
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
  Assignee: unassigned at gcc dot gnu.org
  Reporter: mat at lcs dot mit.edu

templatetypename T T identity(T x) { return x; }

void fail()
{
identity(0U);
identity(__builtin_bswap32(0));
}

$ ~/gcc-4.8.2-install/bin/g++ -c ~/symbol_error.cpp -o ~/symbol_error.o
/tmp/ccojWORv.s: Assembler messages:
/tmp/ccojWORv.s:44: Error: symbol `_Z8identityIjET_S0_' is already defined


It's as if g++ thinks the return type of __builtin_bswap32 is different for
template interning, but the same for name mangling, so it produces bad assembly
code with the same symbol used twice.

This also fails with g++ 4.6.3 and 4.7.2. It works with clang 3.1 and 3.4.

[Bug c++/47011] ICE when using attribute optimize

[mat at lcs dot mit.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47011

--- Comment #2 from Mat Hostetter mat at lcs dot mit.edu 2011-09-20 12:31:56 
UTC ---
Created attachment 25327
  -- http://gcc.gnu.org/bugzilla/attachment.cgi?id=25327
bug showing ICE with -O, incorrect code without optimization

[Bug c++/47011] ICE when using attribute optimize

[mat at lcs dot mit.edu]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47011

--- Comment #3 from Mat Hostetter mat at lcs dot mit.edu 2011-09-20 12:32:47 
UTC ---
I am seeing the same crash with gcc 4.4.[3456], on x86_64. It works on 4.6.1.

I encountered this crash when simply upgrading to the latest boost (1.47.0),
which uses attribute optimize, so this is likely to affect other people.

But the bug is more surprising and subtle than just the crash. It can silently
generate incorrect code, which took me longer to track down.

If you compile my attached code optimized you get the internal compiler error.
If you compile it unoptimized, g++ silently changes the calling convention for
vector::begin from by-value to by-reference -- but only if a completely
unrelated empty function is marked with attribute optimize! 

In the full example this meant g++ miscompiled std::vector::begin to use the
wrong calling convention, which when linked into other objects expecting the
proper calling convention would cause a crash.