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

[David Gibson]

On Tue, May 05, 2020 at 08:26:48AM -0400, Daniele Buono wrote:
> 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.

Yeah, that would be a bit nicer.  Please send the v2.

> 
> > > ---
> > >   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);
> > 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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