Re: [Qemu-devel] [PATCH for-4.1] tcg: Fix constant folding of INDEX_op_extract2_i32

[Christophe Lyon]

On Tue, 9 Jul 2019 at 15:02, Alex Bennée <address@hidden> wrote:
>
>
> Richard Henderson <address@hidden> writes:
>
> > On a 64-bit host, discard any replications of the 32-bit
> > sign bit when performing the shift and merge.
> >
> > Fixes: https://bugs.launchpad.net/bugs/1834496
> > Signed-off-by: Richard Henderson <address@hidden>
>
> Reviewed-by: Alex Bennée <address@hidden>
> Tested-by: Alex Bennée <address@hidden>
>

Tested-by: Christophe Lyon <address@hidden>

Hi,

I ran GCC validations with your fix, it does fix the problems I
reported with the arm-none-linux-gnueabi target.

Unfortunately, we are unlucky because there are still regressions
compared to qemu-3.1 when using the arm-none-linux-gnueabihf target,
as well as arm-eabi and aarch64-elf.
I hoped all had the same root cause..... I'll report the remaining
ones in a new launchpad bug.

Thanks

Christophe


> > ---
> >  tcg/optimize.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/tcg/optimize.c b/tcg/optimize.c
> > index d7c71a6085..d2424de4af 100644
> > --- a/tcg/optimize.c
> > +++ b/tcg/optimize.c
> > @@ -1213,8 +1213,8 @@ void tcg_optimize(TCGContext *s)
> >                  if (opc == INDEX_op_extract2_i64) {
> >                      tmp = (v1 >> op->args[3]) | (v2 << (64 - op->args[3]));
> >                  } else {
> > -                    tmp = (v1 >> op->args[3]) | (v2 << (32 - op->args[3]));
> > -                    tmp = (int32_t)tmp;
> > +                    tmp = (int32_t)(((uint32_t)v1 >> op->args[3]) |
> > +                                    ((uint32_t)v2 << (32 - op->args[3])));
> >                  }
> >                  tcg_opt_gen_movi(s, op, op->args[0], tmp);
> >                  break;
>
>
> --
> Alex Bennée