Re: warning: right shift count >= width of type

[Nathan Sidwell <nathan at codesourcery dot com>]

Dave Korn wrote:
>   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

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

It's _undefined_.  Didn't you make some comment about what undefined
meant last week :)

nathan

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