warning: right shift count >= width of type

["Dave Korn" <dk at artimi dot com>]

  Afternoon all.  Here's something that's piqued my curiosity; it's probably
owing to some language-lawyerly issue, but it isn't obvious to me.  This is
on gcc-3.3.3, (cygwin variant, but that's probably not relevant):

-------------------------<snip!>-------------------------
dk@mace /test/shift-test> cat foo.c

unsigned int bar (unsigned int baz)
{
unsigned int quux;

        quux = baz >> 32;
        return quux;
}

dk@mace /test/shift-test> gcc -S foo.c -O2 -o foo.s
foo.c: In function `bar':
foo.c:7: warning: right shift count >= width of type
dk@mace /test/shift-test> cat foo.s
        .file   "foo.c"
        .text
        .p2align 4,,15
.globl _bar
        .def    _bar;   .scl    2;      .type   32;     .endef
_bar:
        pushl   %ebp
        movl    %esp, %ebp
        movl    8(%ebp), %eax
        movb    $32, %cl
        shrl    %cl, %eax
        popl    %ebp
        ret
dk@mace /test/shift-test>
-------------------------<snip!>-------------------------

  Why isn't the shift operation optimised away and replaced with const_int
0?


    cheers, 
      DaveK
-- 
Can't think of a witty .sigline today....