[Bug c/12826] New: Optimizer removes reference through volatile pointer

["lee at bustech dot com" <gcc-bugzilla at gcc dot gnu dot org>]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=12826

           Summary: Optimizer removes reference through volatile pointer
           Product: gcc
           Version: 2.96 (redhat)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: lee at bustech dot com
                CC: gcc-bugs at gcc dot gnu dot org

(Using standard gcc shipped with RedHat 7.3 Linux)

$ gcc -v -save-temps -O -S t.c
Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/2.96/specs
gcc version 2.96 20000731 (Red Hat Linux 7.3 2.96-113)
 /usr/lib/gcc-lib/i386-redhat-linux/2.96/cpp0 -lang-c -v -D__GNUC__=2
-D__GNUC_MINOR__=96 -D__GNUC_PATCHLEVEL__=0 -D__ELF__ -Dunix -Dlinux -D__ELF__
-D__unix__ -D__linux__ -D__unix -D__linux -Asystem(posix) -D__OPTIMIZE__
-Acpu(i386) -Amachine(i386) -Di386 -D__i386 -D__i386__ -D__tune_i386__ t.c t.i
GNU CPP version 2.96 20000731 (Red Hat Linux 7.3 2.96-113) (cpplib) (i386 Linux/ELF)
ignoring nonexistent directory "/usr/i386-redhat-linux/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib/gcc-lib/i386-redhat-linux/2.96/include
 /usr/include
End of search list.
 /usr/lib/gcc-lib/i386-redhat-linux/2.96/cc1 t.i -quiet -dumpbase t.c -O
-version -o t.s
GNU C version 2.96 20000731 (Red Hat Linux 7.3 2.96-113) (i386-redhat-linux)
compiled by GNU C version 2.96 20000731 (Red Hat Linux 7.3 2.96-113).

Expected behavior:
    Should not optimize out the read of *sp in the loop.
Actual behavior:
    Doesn't read *sp in the loop.