RE: [RFC PATCH v3 25/34] Hexagon (target/hexagon) macros to interface with the generator

[Taylor Simpson]

> -----Original Message-----
> From: Richard Henderson <richard.henderson@linaro.org>
> Sent: Sunday, August 30, 2020 2:59 PM
> To: Taylor Simpson <tsimpson@quicinc.com>; qemu-devel@nongnu.org
> Cc: philmd@redhat.com; laurent@vivier.eu; riku.voipio@iki.fi;
> aleksandar.m.mail@gmail.com; ale@rev.ng
> Subject: Re: [RFC PATCH v3 25/34] Hexagon (target/hexagon) macros to
> interface with the generator
>
> On 8/30/20 1:30 PM, Taylor Simpson wrote:
> >
> >
> >> -----Original Message-----
> >> From: Richard Henderson <richard.henderson@linaro.org>
> >> Sent: Friday, August 28, 2020 6:49 PM
> >> To: Taylor Simpson <tsimpson@quicinc.com>; qemu-devel@nongnu.org
> >> Cc: philmd@redhat.com; laurent@vivier.eu; riku.voipio@iki.fi;
> >> aleksandar.m.mail@gmail.com; ale@rev.ng
> >> Subject: Re: [RFC PATCH v3 25/34] Hexagon (target/hexagon) macros to
> >> interface with the generator
> >>
> >> On 8/18/20 8:50 AM, Taylor Simpson wrote:
> >>> +#define DECL_REG(NAME, NUM, X, OFF) \
> >>> +    TCGv NAME = tcg_temp_local_new(); \
> >>> +    int NUM = REGNO(X) + OFF
> >>> +
> >>> +#define DECL_REG_WRITABLE(NAME, NUM, X, OFF) \
> >>> +    TCGv NAME = tcg_temp_local_new(); \
> >>> +    int NUM = REGNO(X) + OFF; \
> >>> +    do { \
> >>> +        int is_predicated = GET_ATTRIB(insn->opcode, A_CONDEXEC); \
> >>> +        if (is_predicated && !is_preloaded(ctx, NUM)) { \
> >>> +            tcg_gen_mov_tl(hex_new_value[NUM], hex_gpr[NUM]); \
> >>> +        } \
> >>> +    } while (0)
> >>> +/*
> >>> + * For read-only temps, avoid allocating and freeing
> >>> + */
> >>> +#define DECL_REG_READONLY(NAME, NUM, X, OFF) \
> >>> +    TCGv NAME; \
> >>> +    int NUM = REGNO(X) + OFF
> >>> +
> >>> +#define DECL_RREG_d(NAME, NUM, X, OFF) \
> >>> +    DECL_REG_WRITABLE(NAME, NUM, X, OFF)
> >>> +#define DECL_RREG_e(NAME, NUM, X, OFF) \
> >>> +    DECL_REG(NAME, NUM, X, OFF)
> >>
> >> Is there a good reason for all these macros?
> >> Why not just bake this knowledge into gen_tcg_funcs.py?
> >> Seems like it would be just a couple of functions...
> >>
> >> At present, both this and the intermediary files are unreadable.  One has
> to
> >> pass genptr.c through -E and indent to see what's going on.
> >
> > I add the regid...
>
> No, that doesn't answer the question.
>
> Why does DECL_RREG_d et al exist as macros at all?  Why not emit the
> expansions
> directly by gen_tcg_funcs.py?
>
> It seems to me that all this does is obfuscate the code, adding one more layer
> that one has to unwind in order to understand.
>
>
> r~

This is partly historical.  My intent was to keep the generator  simple and 
mechanical and put the optimization and complexity into the macros.  I will 
code this up and see if we think it's better.