Re: [PATCH] Fix the one entry mem{{,p}cpy,move,set} optimization aliasing issues (PR middle-end/29272)

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 9/29/06, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> While the PR29272 testcase is IMHO violating the strict aliasing rules
> (my reading of 6.5 is that for the heap object the first memcpy call gives the
> object struct Node * effective type, so it shouldn't then be accessed as
> int), I believe it is possible to come up with a standard conforming
> testcase for this (e.g. when the object is not allocated, we access it
> mostly through its original type but additionall with memcpy through an
> aliasing incompatible pointer).

Oh, 6.5 is indeed explicit about memcpy.  Changing all pointer types the
testcase uses for freelist handling to char[sizeof(void*)] would make it valid
but completely ugly to look at.

I wonder how the C people thought one would manage memory with these
rules...  (and I wonder how glibc does it, and if it is going to break
if we inline
glibc memory management into user code with LTO one day...)

Richard.