Re: [PATCH][RFC] Introduce BIT_FIELD_INSERT

[Eric Botcazou <ebotcazou@adacore.com>]

> Index: trunk/gcc/tree.def
> ===================================================================
> *** trunk.orig/gcc/tree.def	2016-05-17 17:19:41.783958489 +0200
> --- trunk/gcc/tree.def	2016-05-19 10:23:35.779141973 +0200
> *************** DEFTREECODE (ADDR_EXPR, "addr_expr", tcc
> *** 852,857 ****
> --- 852,871 ----
>      descriptor of type ptr_mode.  */
>   DEFTREECODE (FDESC_EXPR, "fdesc_expr", tcc_expression, 2)
> 
> + /* Given a word, a value and a bit position within the word,
> +    produce the value that results if replacing the parts of word
> +    starting at the bit position with value.
> +    Operand 0 is a tree for the word of integral or vector type;
> +    Operand 1 is a tree for the value of integral or vector element type;
> +    Operand 2 is a tree giving the constant position of the first
> referenced bit; +    The number of bits replaced is given by the precision
> of the value +    type if that is integral or by its size if it is
> non-integral. +    ???  The reason to make the size of the replacement
> implicit is to not +    have a quaternary operation.
> +    The replaced bits shall be fully inside the word.  If the word is of
> +    vector type the replaced bits shall be aligned with its elements.  */
> + DEFTREECODE (BIT_INSERT_EXPR, "bit_field_insert", tcc_expression, 3)
> +

"word" is ambiguous (what is a word of vector type?).  What's allowed as 
operand #0 exactly?  If that's anything, I'd call it a value too, possibly 
with a qualifier, for example:

 /* Given a container value, a replacement value and a bit position within
    the container, produce the value that results from replacing the part of
    the container starting at the bit position with the replacement value.
    Operand 0 is a tree for the container value of integral or vector type;
    Operand 1 is a tree for the replacement value of another integral or
    vector element type;
    Operand 2 is a tree giving the constant bit position;
    The number of bits replaced is given by the precision of the type of the
    replacement value if it is integral or by its size if it is non-integral.
    ???  The reason to make the size of the replacement implicit is to avoid
    introducing a quaternary operation.
    The replaced bits shall be fully inside the container.  If the container
    is of vector type, then these bits shall be aligned with its elements.  */
DEFTREECODE (BIT_INSERT_EXPR, "bit_field_insert", tcc_expression, 3)

-- 
Eric Botcazou