Re: [RFC PATCH] tcg/optimize: only read val after const check

[Richard Henderson <richard.henderson@linaro.org>]

On 2/9/22 01:21, Alex Bennée wrote:
> valgrind pointed out that arg_info()->val can be undefined which will
> be the case if the arguments are not constant. The ordering of the
> checks will have ensured we never relied on an undefined value but for
> the sake of completeness re-order the code to be clear.
> 
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
>   tcg/optimize.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)

Thanks for this.  Just missed today's pull, but applied, finally.


r~

> 
> diff --git a/tcg/optimize.c b/tcg/optimize.c
> index e573000951..06213fd434 100644
> --- a/tcg/optimize.c
> +++ b/tcg/optimize.c
> @@ -552,10 +552,10 @@ static bool do_constant_folding_cond_eq(TCGCond c)
>   static int do_constant_folding_cond(TCGType type, TCGArg x,
>                                       TCGArg y, TCGCond c)
>   {
> -    uint64_t xv = arg_info(x)->val;
> -    uint64_t yv = arg_info(y)->val;
> -
>       if (arg_is_const(x) && arg_is_const(y)) {
> +        uint64_t xv = arg_info(x)->val;
> +        uint64_t yv = arg_info(y)->val;
> +
>           switch (type) {
>           case TCG_TYPE_I32:
>               return do_constant_folding_cond_32(xv, yv, c);
> @@ -567,7 +567,7 @@ static int do_constant_folding_cond(TCGType type, TCGArg x,
>           }
>       } else if (args_are_copies(x, y)) {
>           return do_constant_folding_cond_eq(c);
> -    } else if (arg_is_const(y) && yv == 0) {
> +    } else if (arg_is_const(y) && arg_info(y)->val == 0) {
>           switch (c) {
>           case TCG_COND_LTU:
>               return 0;