Re: [PATCH 1/1] target-ppc: fix rlwimi, rlwinm, rlwnm for Clang-9

[Daniele Buono]

On 5/5/2020 1:08 AM, David Gibson wrote:
> On Fri, May 01, 2020 at 03:09:13PM -0400, Daniele Buono wrote:
> > Starting with Clang v9, -Wtype-limits is implemented and triggers a
> > few "result of comparison is always true" errors when compiling PPC32
> > targets.
> >
> > The comparisons seem to be necessary only on PPC64, since the
> > else branch in PPC32 only has a "g_assert_not_reached();" in all cases.
> >
> > This patch restructures the code so that PPC32 does not execute the
> > check, while PPC64 works like before
> >
> > Signed-off-by: Daniele Buono <address@hidden>
>
> Urgh.  #ifdefs intertangled with if statements gets pretty ugly.  But,
> then, it's already pretty ugly, so, applied.
Agreed, it's very ugly. After I sent the patch I thought of an 
alternative that looks like this:

bool mask_in_32b = true;

#if defined(TARGET_PPC64)
if (mask > 0xffffffffu)
  mask_in_32b = false;
#endif

if (mask_in_32b) {
/* Original if-else untouched using mask_in_32b instead of mask*/

It does have an additional if, but with a bit of luck the compiler may 
optimize it out (at least for the 32bit case).
If you think the final outcome may be better, let me know and I'll send 
a patch v2 like that.

> > ---
> >   target/ppc/translate.c | 34 +++++++++++++++++++---------------
> >   1 file changed, 19 insertions(+), 15 deletions(-)
> >
> > diff --git a/target/ppc/translate.c b/target/ppc/translate.c
> > index 807d14faaa..9400fa2c7c 100644
> > --- a/target/ppc/translate.c
> > +++ b/target/ppc/translate.c
> > @@ -1882,6 +1882,7 @@ static void gen_rlwimi(DisasContext *ctx)
> >           tcg_gen_deposit_tl(t_ra, t_ra, t_rs, sh, me - mb + 1);
> >       } else {
> >           target_ulong mask;
> > +        TCGv_i32 t0;
> >           TCGv t1;
> >   
> >   #if defined(TARGET_PPC64)
> > @@ -1891,20 +1892,20 @@ static void gen_rlwimi(DisasContext *ctx)
> >           mask = MASK(mb, me);
> >   
> >           t1 = tcg_temp_new();
> > +#if defined(TARGET_PPC64)
> >           if (mask <= 0xffffffffu) {
> > -            TCGv_i32 t0 = tcg_temp_new_i32();
> > +#endif
> > +            t0 = tcg_temp_new_i32();
> >               tcg_gen_trunc_tl_i32(t0, t_rs);
> >               tcg_gen_rotli_i32(t0, t0, sh);
> >               tcg_gen_extu_i32_tl(t1, t0);
> >               tcg_temp_free_i32(t0);
> > -        } else {
> >   #if defined(TARGET_PPC64)
> > +        } else {
> >               tcg_gen_deposit_i64(t1, t_rs, t_rs, 32, 32);
> >               tcg_gen_rotli_i64(t1, t1, sh);
> > -#else
> > -            g_assert_not_reached();
> > -#endif
> >           }
> > +#endif
> >   
> >           tcg_gen_andi_tl(t1, t1, mask);
> >           tcg_gen_andi_tl(t_ra, t_ra, ~mask);
> > @@ -1938,7 +1939,9 @@ static void gen_rlwinm(DisasContext *ctx)
> >           me += 32;
> >   #endif
> >           mask = MASK(mb, me);
> > +#if defined(TARGET_PPC64)
> >           if (mask <= 0xffffffffu) {
> > +#endif
> >               if (sh == 0) {
> >                   tcg_gen_andi_tl(t_ra, t_rs, mask);
> >               } else {
> > @@ -1949,15 +1952,13 @@ static void gen_rlwinm(DisasContext *ctx)
> >                   tcg_gen_extu_i32_tl(t_ra, t0);
> >                   tcg_temp_free_i32(t0);
> >               }
> > -        } else {
> >   #if defined(TARGET_PPC64)
> > +        } else {
> >               tcg_gen_deposit_i64(t_ra, t_rs, t_rs, 32, 32);
> >               tcg_gen_rotli_i64(t_ra, t_ra, sh);
> >               tcg_gen_andi_i64(t_ra, t_ra, mask);
> > -#else
> > -            g_assert_not_reached();
> > -#endif
> >           }
> > +#endif
> >       }
> >       if (unlikely(Rc(ctx->opcode) != 0)) {
> >           gen_set_Rc0(ctx, t_ra);
> > @@ -1972,6 +1973,9 @@ static void gen_rlwnm(DisasContext *ctx)
> >       TCGv t_rb = cpu_gpr[rB(ctx->opcode)];
> >       uint32_t mb = MB(ctx->opcode);
> >       uint32_t me = ME(ctx->opcode);
> > +    TCGv_i32 t0;
> > +    TCGv_i32 t1;
> > +
> >       target_ulong mask;
> >   
> >   #if defined(TARGET_PPC64)
> > @@ -1980,9 +1984,11 @@ static void gen_rlwnm(DisasContext *ctx)
> >   #endif
> >       mask = MASK(mb, me);
> >   
> > +#if defined(TARGET_PPC64)
> >       if (mask <= 0xffffffffu) {
> > -        TCGv_i32 t0 = tcg_temp_new_i32();
> > -        TCGv_i32 t1 = tcg_temp_new_i32();
> > +#endif
> > +        t0 = tcg_temp_new_i32();
> > +        t1 = tcg_temp_new_i32();
> >           tcg_gen_trunc_tl_i32(t0, t_rb);
> >           tcg_gen_trunc_tl_i32(t1, t_rs);
> >           tcg_gen_andi_i32(t0, t0, 0x1f);
> > @@ -1990,17 +1996,15 @@ static void gen_rlwnm(DisasContext *ctx)
> >           tcg_gen_extu_i32_tl(t_ra, t1);
> >           tcg_temp_free_i32(t0);
> >           tcg_temp_free_i32(t1);
> > -    } else {
> >   #if defined(TARGET_PPC64)
> > +    } else {
> >           TCGv_i64 t0 = tcg_temp_new_i64();
> >           tcg_gen_andi_i64(t0, t_rb, 0x1f);
> >           tcg_gen_deposit_i64(t_ra, t_rs, t_rs, 32, 32);
> >           tcg_gen_rotl_i64(t_ra, t_ra, t0);
> >           tcg_temp_free_i64(t0);
> > -#else
> > -        g_assert_not_reached();
> > -#endif
> >       }
> > +#endif
> >   
> >       tcg_gen_andi_tl(t_ra, t_ra, mask);
> >