Re: [9fans] Conversion of constants in C compiler

[ori@eigenstate.org]

Quoth adr <adr@SDF.ORG>:
> On Wed, 20 Apr 2022, ori@eigenstate.org wrote:
> > When you have a patch, let me know -- I'll happily test
> > and apply to 9front.
> 
> Hi ori, this patch applyes to the sources served at 9front.org.
> By the way, do you plan to keep in sync
> http://only9fans.com/ori/git9/HEAD/info.html or should I forget
> about that repo?
> 
> Regards,
> adr.
> 
> --- /n/9front/sys/src/cmd/cc/lex.c      Wed Apr  6 14:45:26 2022
> +++ /tmp/lex.c  Thu Apr 21 08:39:14 2022
> @@ -848,16 +848,9 @@
>                 yyerror("overflow in constant");
> 
>         vv = yylval.vval;
> -       /*
> -        * c99 is silly: decimal constants stay signed,
> -        * hex and octal go unsigned before widening.
> -        */
> -       w = 32;
> -       if((c1 & (Numdec|Numuns)) == Numdec)
> -               w = 31;
> -       if(c1 & Numvlong || (c1 & Numlong) == 0 && (uvlong)vv >= 1ULL<<w){
> -               if((c1&(Numdec|Numvlong)) == Numdec && vv < 1ULL<<32)
> -                       warn(Z, "int constant widened to vlong: %s", symb);
> +       if(c1 & Numvlong ||
> +         convvtox(vv, TUVLONG) > convvtox(vv, TULONG) ||
> +         (c1 & (Numdec|Numuns)) == Numdec && convvtox(vv, TLONG) < 0) {
>                 if((c1 & Numuns) || convvtox(vv, TVLONG) < 0) {
>                         c = LUVLCONST;
>                         t = TUVLONG;

Thanks for the patch!

I think this gets the condition slightly wrong. For a decimal
number, we should promote:

        int -> long -> vlong.

For a hex number, though, we want

        int -> uint -> long -> ulong -> vlong -> uvlong

however with the condition above,

        18446744073709551615

will get converted to a uvlong:

        c1 & Numvlong == 0:
                false -> no explicit conversion
        convvtox(vv, TUVLONG) > convvtox(vv, TULONG)
                true -> vv fits into a uvlong, but not a ulong,
                so we enter this.

so then, we end up in this branch:

        if((c1 & Numuns) || convvtox(vv, TVLONG) < 0) {

                true, because convvtox(vv, TVLONG) < 0.

I think we want:

        if(c1 & Numvlong ||
          convvtox(vv, TUVLONG) != convvtox(vv, TULONG) ||
          convvtox(vv, TLONG) < 0) {
                if((c1 & (Numdec|Numuns)) == 0 &&
                  ((c1 & Numuns) || convvtox(vv, TVLONG) < 0)) {
                        c = LUVLCONST;
                        t = TUVLONG;
                        goto nret;
                }
                c = LVLCONST;
                t = TVLONG;
                goto nret;
        }
        if(c1 & Numlong ||
          convvtox(vv, TULONG) > convvtox(vv, TUINT) ||
          convvtox(vv, TINT) < 0) {
                if((c1 & (Numdec|Numuns)) == 0 && 
                  ((c1 & Numuns) || convvtox(vv, TLONG) < 0)) {
                        c = LULCONST;
                        t = TULONG;
                        goto nret;
                }
                c = LLCONST;
                t = TLONG;
                goto nret;
        }


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