[Bug optimization/12082] New: Inappropriate unreachable code warnings

[augart at us dot ibm dot com]

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12082

           Summary: Inappropriate unreachable code warnings
           Product: gcc
           Version: 3.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: augart at us dot ibm dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu

Options given when GCC was configured/built:
  I configured gcc 3.3.1 with no options; just invoked it as ./configure.

Command line that triggers the bug:
  g++ -v --save-temps -Wunreachable-code  -O3 preprocessModifiedFiles.C -o
preprocessModifiedFiles

Compiler output:

g++ -v --save-temps -Wunreachable-code  -O3 preprocessModifiedFiles.C -o
preprocessModifiedFiles
Reading specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/specs
Configured with: ./configure --cache-file=config.cache
Thread model: posix
gcc version 3.3.1
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/cc1plus -E -D__GNUG__=3 -quiet
-v -D__GNUC__=3 -D__GNUC_MINOR__=3 -D__GNUC_PATCHLEVEL__=1 -D_GNU_SOURCE
preprocessModifiedFiles.C -Wunreachable-code -O3 preprocessModifiedFiles.ii
ignoring nonexistent directory "NONE/include"
ignoring nonexistent directory "/usr/local/i686-pc-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include/c++/3.3.1
 /usr/local/include/c++/3.3.1/i686-pc-linux-gnu
 /usr/local/include/c++/3.3.1/backward
 /usr/local/include
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/include
 /usr/include
End of search list.
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/cc1plus -fpreprocessed
preprocessModifiedFiles.ii -quiet -dumpbase preprocessModifiedFiles.C -auxbase
preprocessModifiedFiles -O3 -Wunreachable-code -version -o preprocessModifiedFiles.s
GNU C++ version 3.3.1 (i686-pc-linux-gnu)
	compiled by GNU C version 3.3.
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
preprocessModifiedFiles.C: In function `int main(int, char**)':
preprocessModifiedFiles.C:1147: warning: will never be executed
preprocessModifiedFiles.C:1147: warning: will never be executed
preprocessModifiedFiles.C:1147: warning: will never be executed
preprocessModifiedFiles.C: In function `int preprocess(const char*, const 
   char*)':
preprocessModifiedFiles.C:773: warning: will never be executed
preprocessModifiedFiles.C:753: warning: will never be executed
preprocessModifiedFiles.C:732: warning: will never be executed
preprocessModifiedFiles.C:747: warning: will never be executed
preprocessModifiedFiles.C:631: warning: will never be executed
preprocessModifiedFiles.C:631: warning: will never be executed
preprocessModifiedFiles.C:629: warning: will never be executed
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/../../../../i686-pc-linux-gnu/bin/as -V -Qy -o preprocessModifiedFiles.o preprocessModifiedFiles.s
GNU assembler version 2.14 (i686-pc-linux-gnu) using BFD version 2.14 20030612
 /usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/collect2 --eh-frame-hdr -m
elf_i386 -dynamic-linker /lib/ld-linux.so.2 -o preprocessModifiedFiles
/usr/lib/crt1.o /usr/lib/crti.o
/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/crtbegin.o
-L/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1
-L/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/../../../../i686-pc-linux-gnu/lib
-L/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/../../..
preprocessModifiedFiles.o -lstdc++ -lm -lgcc_s -lgcc -lc -lgcc_s -lgcc
/usr/local/lib/gcc-lib/i686-pc-linux-gnu/3.3.1/crtend.o /usr/lib/crtn.o


I will attach the compressed preprocessed file preprocessModifiedFiles.ii after
I've submitted this report to Bugzilla; don't see how to do so upon bug creation.

Why I think this is a bug:
I believe the "will never be executed" warnings are incorrect.

Additional details:
I am running on an IBM Netvista type 6792-MHU computer, under a Red 
Hat 7.3 GNU/Linux distribution.  Linux kernel 2.40.20, 1536MB of RAM,
1GB of swap space.  Pentium 4 (1.80 GHz processor).  Please let me
know if I can provide you with additional information.

I compiled GCC myself from the 3.3.1 tarball, using gcc 2.96.  The
build and install completed normally.  Before I compiled gcc, I
compiled and installed binutils 2.14:

  Bash$ gcc --version
  gcc (GCC) 3.3.1
  [...]
  Bash$ as --version
  GNU assembler 2.14 20030612
  [...]

I have tried to trim down the program text I'm appending, but the
really short versions don't show the warning.  

Sincerely Yours,

--Steven Augart
  Jikes RVM Open Source Java Compiler Project
  http://www.ibm.com/developerworks/oss/jikesrvm/