On Mon, Aug 15, 2011 at 2:42 PM, Richard Guenther <rguent...@suse.de> wrote:
>
> The g++.dg/init/copy7.C testcase checks whether the C++ frontend
> guards memcpy it emits via a conditional verifying that src != dst
> because calling memcpy with overlapping source / destination is
> not supported.
>
> The testcase is misguided though (and the C++ frontend was, until
> recently) - the middle-end itself will replace aggregate copies
> with memcpy libcalls if it suits - without such conditional.
> As PR39480 shows (the bug that prompted to "fixing" the C++ frontend),
> the "error" was diagnosed by valgrind, not any real memcpy implemenation.
>
> The argument still holds that no reasonable memcpy implementation
> will reject the src == dest case. Arguing about explicit cache
> write-allocation is moot, as you'd still have to handle the
> case of memcpy (&a, &a+1, 1) correctly - and thus any reasonable
> implementation would handle the src == dest case explicitly if
> that is necessary.
>
> Thus, the following simply removes the now FAILing testcase on
> the basis that it never was PASSing really (as my modified
> C testcases in PR50079 show). If we ever encounter a platform
> that fails for memcpy (&a, &a, ...) and we decide it's not the
> platform that is broken we have to invent a fix in the middle-end
> and (conditionally) guard any libcall block moves.
>
> Comments? Ok to commit?
Ping? Richard? Jason?
Thanks,
Richard.
> Thanks,
> Richard.
>
> 2011-08-15 Richard Guenther <rguent...@suse.de>
>
> PR middle-end/50079
> * g++.dg/init/copy7.C: Remove testcase.
>
> Index: gcc/testsuite/g++.dg/init/copy7.C
> ===================================================================
> --- gcc/testsuite/g++.dg/init/copy7.C (revision 177759)
> +++ gcc/testsuite/g++.dg/init/copy7.C (working copy)
> @@ -1,39 +0,0 @@
> -// PR c++/39480
> -// It isn't always safe to call memcpy with identical arguments.
> -// { dg-do run }
> -
> -extern "C" void abort();
> -extern "C" void *
> -memcpy(void *dest, void *src, __SIZE_TYPE__ n)
> -{
> - if (dest == src)
> - abort();
> - else
> - {
> - __SIZE_TYPE__ i;
> - for (i = 0; i < n; i++)
> - ((char *)dest)[i] = ((const char*)src)[i];
> - }
> -}
> -
> -struct A
> -{
> - double d[10];
> -};
> -
> -struct B: public A
> -{
> - char bc;
> -};
> -
> -B b;
> -
> -void f(B *a1, B* a2)
> -{
> - *a1 = *a2;
> -}
> -
> -int main()
> -{
> - f(&b,&b);
> -}
>
