On Thu, 30 Sept 2021 at 06:44, David Gibson <da...@gibson.dropbear.id.au> wrote:
>
> From: Cédric Le Goater <c...@kaod.org>
>
> The current way the mask is built can overflow with a 64-bit decrementer.
> Use sextract64() to extract the signed values and remove the logic to
> handle negative values which has become useless.
>
> Cc: Luis Fernando Fujita Pires <luis.pi...@eldorado.org.br>
> Fixes: a8dafa525181 ("target/ppc: Implement large decrementer support for
> TCG")
> Signed-off-by: Cédric Le Goater <c...@kaod.org>
> Message-Id: <20210920061203.989563-5-...@kaod.org>
> Reviewed-by: Luis Pires <luis.pi...@eldorado.org.br>
> Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
Hi; Coverity complains about dead code here (CID 1464061):
> * On MSB edge based DEC implementations the MSB going from 0 -> 1
> triggers
> * an edge interrupt, so raise it here too.
> */
> - if ((value < 3) ||
> - ((tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL) && negative) ||
> - ((tb_env->flags & PPC_DECR_UNDERFLOW_TRIGGERED) && negative
> - && !(decr & (1ULL << (nr_bits - 1))))) {
> + if ((signed_value < 3) ||
> + ((tb_env->flags & PPC_DECR_UNDERFLOW_LEVEL) && signed_value < 0) ||
> + ((tb_env->flags & PPC_DECR_UNDERFLOW_TRIGGERED) && signed_value < 0
> + && signed_decr >= 0)) {
> (*raise_excp)(cpu);
> return;
> }
If signed_value < 3 then the first clause of the || evaluates as true,
and so we will definitely take the if() clause. So if we're evaluating
the second operand to the || then we know that signed_value > 3,
which means that 'signed_value < 0' is always false and in turn that
neither of the other two '||' options can be true. The whole expression
is equivalent to just "if (signed_value < 3)".
What was intended here? If this was supposed to be a no-behaviour-change
commit (apart from fixing the 64-bit case) then the condition should
have stayed as "(value < 3)", I think.
thanks
-- PMM
