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Date: Wed, 20 Sep 2023 17:02:36 +0300 (MSK)
From: Alexander Monakov <amonakov@ispras.ru>
To: Richard Biener <rguenther@suse.de>
cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH][RFC] middle-end/106811 - document GENERIC/GIMPLE undefined
 behavior
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On Fri, 15 Sep 2023, Richard Biener via Gcc-patches wrote:

> +@itemize @bullet
> +@item
> +When the result of negation, addition, subtraction or division of two signed
> +integers or signed integer vectors not subject to @option{-fwrapv} cannot be
> +represented in the type.

It would be a bit awkward to add 'or vectors' everywhere it applies, perhaps
say something general about elementwise vector operations up front?

> +
> +@item
> +The value of the second operand of any of the division or modulo operators
> +is zero.
> +
> +@item
> +When incrementing or decrementing a pointer not subject to
> +@option{-fwrapv-pointer} wraps around zero.
> +
> +@item
> +An expression is shifted by a negative number or by an amount greater
> +than or equal to the width of the shifted operand.
> +
> +@item
> +Pointers that do not point to the same object are compared using
> +relational operators.

This does not apply to '==' and '!='. Maybe say

  Ordered comparison operators are applied to pointers
  that do not point to the same object.

> +
> +@item
> +An object which has been modified is accessed through a restrict-qualified
> +pointer and another pointer that are not both based on the same object.
> +
> +@item
> +The @} that terminates a function is reached, and the value of the function
> +call is used by the caller.
> +
> +@item
> +When program execution reaches __builtin_unreachable.
> +
> +@item
> +When an object has its stored value accessed by an lvalue that
> +does not have one of the following types:
> +@itemize @minus
> +@item
> +a (qualified) type compatible with the effective type of the object
> +@item
> +a type that is the (qualified) signed or unsigned type corresponding to
> +the effective type of the object
> +@item
> +a character type, a ref-all qualified type or a type subject to
> +@option{-fno-strict-aliasing}
> +@item
> +a pointer to void with the same level of indirection as the accessed
> +pointer object
> +@end itemize

This list seems to miss a clause that allows aliasing between
scalar types and their vector counterparts?

Thanks.
Alexander