[Bug optimization/12082] Inappropriate unreachable code warnings

["augart at us dot ibm dot com" <gcc-bugzilla at gcc dot gnu dot org>]

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



------- Additional Comments From augart at us dot ibm dot com  2003-08-28 17:25 -------
I have found a smaller test case that shows the bug (down to 36 lines including
7 blank lines).  

I am attaching "bad1.i", a preprocessed C file that triggers the warning.

Here is the output from compiling bad1.i with gcc 3.3.1:
bilbo:~/JikesRVM/gccbug > cc --save-temps -v -Wunreachable-code -O3 -o bad1.S -S
bad1.i
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/cc1 -fpreprocessed bad1.i -quiet
-dumpbase bad1.i -auxbase-strip bad1.S -O3 -Wunreachable-code -version -o bad1.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
bad1.c: In function `main':
bad1.c:13: warning: will never be executed
bilbo:~/JikesRVM/gccbug > 

The bug does not appear when I compile the very similar source file good1.c:

bilbo:~/JikesRVM/gccbug > cc --save-temps -v -Wunreachable-code -O3 -o good1.S
-S good1.i
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/cc1 -fpreprocessed good1.i
-quiet -dumpbase good1.i -auxbase-strip good1.S -O3 -Wunreachable-code -version
-o good1.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
bilbo:~/JikesRVM/gccbug > 

Nor does it appear when I compile good2.i, which is bad1.i without the for loop:

bilbo:~/JikesRVM/gccbug > cc --save-temps -v -Wunreachable-code -O3 -o good2.S
-S good2.i
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/cc1 -fpreprocessed good2.i
-quiet -dumpbase good2.i -auxbase-strip good2.S -O3 -Wunreachable-code -version
-o good2.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
bilbo:~/JikesRVM/gccbug >