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Re: [PATCH RFC] gimplefe: expose MULT_HIGHPART_EXPR


On Fri, Aug 17, 2018 at 3:09 PM Alexander Monakov <amonakov@ispras.ru> wrote:
>
> For testing generic expansion of MULT_HIGHPART_EXPR I chose to expose it
> via the GIMPLE FE with the following patch.
>
> "h*" is how tree-pretty-print dumps MULT_HIGHPART_EXPR.
>
> This patch accepts "h<whitespace>*" which ideally shouldn't happen, but
> I don't see a simple way to fix that.
>
> Is this desirable for trunk?
>
> Is there general policy for how fancy tree codes should be exposed in
> the GIMPLE FE?

We generally use __FOO (__ABS, __ABSU, __MEM), so I'd prefer
__MULT_HIGHPART, though while the existing examples parse
nicely for humans binary operands are somewhat awkward here
and thus a function-style __MULT_HIGHPART would be easier to read.

For example for POINTER_PLUS_EXPR we decide based on the type
context what '+' maps to.  Applying that to '*' and MULT_HIGHPART_EXPR
looks possible as well but I guess it would be non-obvious as well.

I suppose a case that will arise at some point is the need for
EXACT_DIV_EXPR which is also not supported right now and dumped
as '/[ex]' currently.

So if you think

 z = x __MULT_HIGHPART y;

is fine then please go with that instead.  And yes, the GIMPLE FE
should eventually support all of GIMPLE.

Richard.

>         * c/gimple-parser.c (c_parser_gimple_statement): Add "h*" for
>         MULT_HIGHPART_EXPR.
>
> diff --git a/gcc/c/gimple-parser.c b/gcc/c/gimple-parser.c
> index 1be5d14dc2d..cf05c936166 100644
> --- a/gcc/c/gimple-parser.c
> +++ b/gcc/c/gimple-parser.c
> @@ -450,6 +450,7 @@ c_parser_gimple_statement (c_parser *parser, gimple_seq *seq)
>
>     gimple-binary-expression:
>       gimple-unary-expression * gimple-unary-expression
> +     gimple-unary-expression h* gimple-unary-expression
>       gimple-unary-expression / gimple-unary-expression
>       gimple-unary-expression % gimple-unary-expression
>       gimple-unary-expression + gimple-unary-expression
> @@ -544,6 +545,18 @@ c_parser_gimple_binary_expression (c_parser *parser)
>      case CPP_OR_OR:
>        c_parser_error (parser, "%<||%> not valid in GIMPLE");
>        return ret;
> +    case CPP_NAME:
> +       {
> +         tree id = c_parser_peek_token (parser)->value;
> +         if (strcmp (IDENTIFIER_POINTER (id), "h") == 0
> +             && c_parser_peek_2nd_token (parser)->type == CPP_MULT)
> +           {
> +             c_parser_consume_token (parser);
> +             code = MULT_HIGHPART_EXPR;
> +             break;
> +           }
> +       }
> +      /* Fallthru.  */
>      default:
>        /* Not a binary expression.  */
>        return lhs;


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