[Bug rtl-optimization/21402] wrong-code with inlining and type-punned pointer
schlie at comcast dot net
gcc-bugzilla@gcc.gnu.org
Sat May 21 21:28:00 GMT 2005
------- Additional Comments From schlie at comcast dot net 2005-05-21 21:28 -------
(In reply to comment #4)
> Subject: Re: wrong-code with inlining and type-punned pointer
> Because this is what the standard says is allowed. The standard also
> says the comparisons and assignment between pointers without a case is
> invalid code and should be diagnostic. Again this is what the standard
> says for these things and GCC follows the C standard.
Here's an interesting portion of the standard, which seems to direcly imply
that signed and unsigned lvalue references are presumed to validly alias; so
so this should place both in the same alias set, and potentially eliminate the
default warning when comparing pointers which differ only in signness, as
it seems a little silly if they may factually alias each other:
6.3 Expressions
[#7] An object shall have its stored value accessed only by
an lvalue expression that has one of the following types:59
- a type compatible with the effective type of the
object,
- a qualified version of a type compatible with the
effective type of the object,
- a type that is the signed or unsigned type
corresponding to the effective type of the object,
- a type that is the signed or unsigned type
corresponding to a qualified version of the effective
__________
59. The intent of this list is to specify those
circumstances in which an object may or may not be
aliased.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21402
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