https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67281
--- Comment #4 from Tulio Magno Quites Machado Filho <tuliom at linux dot
vnet.ibm.com> ---
(In reply to Andrew Pinski from comment #3)
> Since there are no stores, the load seems like it can be pulled out of the
> loop too.
I disagree with you.
If I use the value of dest to take a decision inside the transaction, I need
the memory barrier before the access to *src0.
Here's an example:
long
foo (long dest, long *src0, long src1, long tries)
{
long i;
for (i = 0; i < tries; i++)
{
__builtin_tbegin (0);
dest = *src0 + src1;
if (dest == 13)
__builtin_tabort(0);
__builtin_tend (0);
}
return dest;
}
In other words, if you access *src0 before the memory barrier, its value may
change when the memory barrier is created. This is particularly useful if dest
says if a lock has been acquired by another thread or not.
For the reference, this has been found in glibc source code:
https://sourceware.org/ml/libc-alpha/2015-07/msg00986.html
