Re: [Qemu-devel] [PATCH 3/3] disas/arm: avoid clang shifting negative signed warning

[Paolo Bonzini]

On 10/11/2015 16:57, Stefan Hajnoczi wrote:
> clang 3.7.0 on x86_64 warns about the following:
> 
>   disas/arm.c:1782:17: warning: shifting a negative signed value is undefined 
> [-Wshift-negative-value]
>     imm |= (-1 << 7);
>             ~~ ^
> 
> Note that this patch preserves the tab indent in this source file
> because the surrounding code still uses tabs.
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>

I would like to know a case where (except with ubsan) clang actually
uses the optimization.

If not, this is just error message theatre (which is not news for clang)
and shouldn't have been part of -Wall.

Paolo