[Bug middle-end/29239] New: -fno-strict-aliasing disables restrict

[acahalan at gmail dot com]

This really shouldn't happen. Rather than disabling the whole
analysis, -fno-strict-aliasing should should simply cause gcc
to use the (char*) rules for everything.

It can be useful to add "restrict", even if it is not
practical to find and fix all aliasing-related problems.

$ cat restrict.c
void foo(int *restrict a, int *restrict b, int *restrict c){
        *a = *b;
        *c = *b;
}
$ gcc -m32 -std=gnu99 -mregparm=3 -fomit-frame-pointer -Os -S restrict.c
$ cat restrict.s
        .file   "restrict.c"
        .text
.globl foo
        .type   foo, @function
foo:
        movl    (%edx), %edx
        movl    %edx, (%eax)
        movl    %edx, (%ecx)
        ret
        .size   foo, .-foo
        .ident  "GCC: (GNU) 4.1.1 20060828 (Red Hat 4.1.1-20)"
        .section        .note.GNU-stack,"",@progbits
$ gcc -m32 -std=gnu99 -mregparm=3 -fomit-frame-pointer -Os -fno-strict-aliasing
-S restrict.c
$ cat restrict.s
        .file   "restrict.c"
        .text
.globl foo
        .type   foo, @function
foo:
        pushl   %ebx
        movl    (%edx), %ebx
        movl    %ebx, (%eax)
        movl    (%edx), %eax
        popl    %ebx
        movl    %eax, (%ecx)
        ret
        .size   foo, .-foo
        .ident  "GCC: (GNU) 4.1.1 20060828 (Red Hat 4.1.1-20)"
        .section        .note.GNU-stack,"",@progbits
$ 

BTW, this is probably related to the problem of -fno-strict-aliasing
silently disabling the -Wstrict-aliasing=2 warning option.


-- 
           Summary: -fno-strict-aliasing disables restrict
           Product: gcc
           Version: 4.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: acahalan at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29239