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* [Bug c++/12667] New: max(enum) returns reference to temporary
@ 2003-10-18  0:15 mdorey at bluearc dot com
  2003-10-18  0:46 ` [Bug c++/12667] " pinskia at gcc dot gnu dot org
                   ` (10 more replies)
  0 siblings, 11 replies; 12+ messages in thread
From: mdorey at bluearc dot com @ 2003-10-18  0:15 UTC (permalink / raw)
  To: gcc-bugs

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12667

           Summary: max(enum) returns reference to temporary
           Product: gcc
           Version: 3.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mdorey at bluearc dot com
                CC: gcc-bugs at gcc dot gnu dot org

I think that max1() and max2() are both legal and should generate equivalent, 
legal code:

enum E {
    E1, E2
};
const E& max1(const E& a, const E& b) {
  bool c = a < b;
  return c ? b : a;
}
const E& max2(const E& a, const E& b) {
  return a < b ? b : a;
}

max2(), however, provokes a warning:

max-enum.cpp: In function `const E& max2(const E&, const E&)':
max-enum.cpp:9: warning: returning reference to temporary

And, worse, the warning's accurate in that, I think, incorrect code is 
generated.  I'm a PowerPC weenie at the moment, so this is the clearest 
demonstration of the problem in my eyes (3.3.1 sadly):

trevithick:~/playpen$ powerpc-eabi-g++ -W -Wall -pedantic -v -O2 -c max-
enum.cpp 
Reading specs from /usr/local/lib/gcc-lib/powerpc-eabi/3.3.1/specs
Configured with: ../gcc-3.3.1/configure --target=powerpc-eabi --with-newlib --
with-local-prefix=/usr/local/powerpc-eabi --enable-languages=c,c++ --enable-cxx-
flags=-fno-exceptions
Thread model: single
gcc version 3.3.1
 /usr/local/lib/gcc-lib/powerpc-eabi/3.3.1/cc1plus -quiet -v -D__GNUC__=3 -
D__GNUC_MINOR__=3 -D__GNUC_PATCHLEVEL__=1 max-enum.cpp -D__GNUG__=3 -quiet -
dumpbase max-enum.cpp -auxbase max-enum -O2 -W -Wall -pedantic -version -
o /tmp/cchuQIuU.s
GNU C++ version 3.3.1 (powerpc-eabi)
        compiled by GNU C version 3.3.1 (Debian).
GGC heuristics: --param ggc-min-expand=98 --param ggc-min-heapsize=129171
ignoring nonexistent directory "NONE/include"
ignoring nonexistent directory "/usr/local/powerpc-eabi/sys-include"
ignoring nonexistent directory "/usr/local/powerpc-eabi/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include/c++/3.3.1
 /usr/local/include/c++/3.3.1/powerpc-eabi
 /usr/local/include/c++/3.3.1/backward
 /usr/local/lib/gcc-lib/powerpc-eabi/3.3.1/include
End of search list.
max-enum.cpp: In function `const E& max2(const E&, const E&)':
max-enum.cpp:9: warning: returning reference to temporary
 /usr/local/lib/gcc-lib/powerpc-eabi/3.3.1/../../../../powerpc-eabi/bin/as -
mppc -V -Qy -o max-enum.o /tmp/cchuQIuU.s
GNU assembler version 2.14 (powerpc-eabi) using BFD version 2.14 20030612
trevithick:~/playpen$ powerpc-eabi-objdump --disassemble max-enum.o

max-enum.o:     file format elf32-powerpc

Disassembly of section .text:

00000000 <_Z4max1RK1ES1_>:
   0:   81 23 00 00     lwz     r9,0(r3)
   4:   7c 6b 1b 78     mr      r11,r3
   8:   80 04 00 00     lwz     r0,0(r4)
   c:   7c 83 23 78     mr      r3,r4
  10:   7c 09 00 00     cmpw    r9,r0
  14:   4d 80 00 20     bltlr   
  18:   7d 63 5b 78     mr      r3,r11
  1c:   4e 80 00 20     blr

00000020 <_Z4max2RK1ES1_>:
  20:   94 21 ff f0     stwu    r1,-16(r1)
  24:   38 61 00 08     addi    r3,r1,8
  28:   38 21 00 10     addi    r1,r1,16
  2c:   4e 80 00 20     blr
trevithick:~/playpen$ 

But the problem is also exhibited in the unoptimised build (I can follow-up 
with the disassembly if you like) and in 3.3.2 Intel builds:

trevithick:~/playpen$ g++ -W -Wall -pedantic -v -O2 -c max-enum.cpp 
Reading specs from /usr/lib/gcc-lib/i486-linux/3.3.2/specs
Configured with: ../src/configure -v --enable-
languages=c,c++,java,f77,pascal,objc,ada,treelang --prefix=/usr --
mandir=/usr/share/man --infodir=/usr/share/info --with-gxx-include-
dir=/usr/include/c++/3.3 --enable-shared --with-system-zlib --enable-nls --
without-included-gettext --enable-__cxa_atexit --enable-clocale=gnu --enable-
debug --enable-java-gc=boehm --enable-java-awt=xlib --enable-objc-gc i486-linux
Thread model: posix
gcc version 3.3.2 20031005 (Debian prerelease)
 /usr/lib/gcc-lib/i486-linux/3.3.2/cc1plus -quiet -v -D__GNUC__=3 -
D__GNUC_MINOR__=3 -D__GNUC_PATCHLEVEL__=2 -D_GNU_SOURCE max-enum.cpp -
D__GNUG__=3 -quiet -dumpbase max-enum.cpp -auxbase max-enum -O2 -W -Wall -
pedantic -version -o /tmp/ccyKxhqp.s
GNU C++ version 3.3.2 20031005 (Debian prerelease) (i486-linux)
        compiled by GNU C version 3.3.2 20031005 (Debian prerelease).
GGC heuristics: --param ggc-min-expand=98 --param ggc-min-heapsize=129171
ignoring nonexistent directory "/usr/i486-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/3.3
 /usr/include/c++/3.3/i486-linux
 /usr/include/c++/3.3/backward
 /usr/local/include
 /usr/lib/gcc-lib/i486-linux/3.3.2/include
 /usr/include
End of search list.
max-enum.cpp: In function `const E& max2(const E&, const E&)':
max-enum.cpp:9: warning: returning reference to temporary
 as -V -Qy -o max-enum.o /tmp/ccyKxhqp.s
GNU assembler version 2.14.90.0.6 (i386-linux) using BFD version 2.14.90.0.6 
20030820 Debian GNU/Linux
trevithick:~/playpen$ objdump --disassemble max-enum.o

max-enum.o:     file format elf32-i386

Disassembly of section .text:

00000000 <_Z4max1RK1ES1_>:
   0:   55                      push   %ebp
   1:   89 e5                   mov    %esp,%ebp
   3:   8b 55 0c                mov    0xc(%ebp),%edx
   6:   8b 4d 08                mov    0x8(%ebp),%ecx
   9:   8b 02                   mov    (%edx),%eax
   b:   39 01                   cmp    %eax,(%ecx)
   d:   7d 04                   jge    13 <_Z4max1RK1ES1_+0x13>
   f:   89 d0                   mov    %edx,%eax
  11:   5d                      pop    %ebp
  12:   c3                      ret    
  13:   89 c8                   mov    %ecx,%eax
  15:   eb fa                   jmp    11 <_Z4max1RK1ES1_+0x11>
  17:   90                      nop    
  18:   90                      nop    
  19:   8d b4 26 00 00 00 00    lea    0x0(%esi,1),%esi

00000020 <_Z4max2RK1ES1_>:
  20:   55                      push   %ebp
  21:   89 e5                   mov    %esp,%ebp
  23:   83 ec 04                sub    $0x4,%esp
  26:   89 ec                   mov    %ebp,%esp
  28:   8d 45 fc                lea    0xfffffffc(%ebp),%eax
  2b:   5d                      pop    %ebp
  2c:   c3                      ret    
  2d:   90                      nop    
  2e:   89 f6                   mov    %esi,%esi
trevithick:~/playpen$ 

The problem doesn't happen if E is typedef()d to be int.


^ permalink raw reply	[flat|nested] 12+ messages in thread
end of thread, other threads:[~2003-12-22 22:57 UTC | newest]

Thread overview: 12+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2003-10-18  0:15 [Bug c++/12667] New: max(enum) returns reference to temporary mdorey at bluearc dot com
2003-10-18  0:46 ` [Bug c++/12667] " pinskia at gcc dot gnu dot org
2003-11-15 11:31 ` [Bug c++/12667] [3.3 regression] " pinskia at gcc dot gnu dot org
2003-11-15 14:07 ` mdorey at bluearc dot com
2003-11-16 17:47 ` bangerth at dealii dot org
2003-11-16 17:55 ` falk at debian dot org
2003-11-18  5:28 ` pinskia at gcc dot gnu dot org
2003-11-19  4:23 ` gdr at integrable-solutions dot net
2003-11-20  7:16 ` mdorey at bluearc dot com
2003-11-20  7:18 ` pinskia at gcc dot gnu dot org
2003-11-20  7:23 ` mdorey at bluearc dot com
2003-12-22 23:30 ` pinskia at gcc dot gnu dot org

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