On 02/28/2017 05:59 AM, Prathamesh Kulkarni wrote:
On 28 February 2017 at 15:40, Jakub Jelinek <ja...@redhat.com> wrote:
On Tue, Feb 28, 2017 at 03:33:11PM +0530, Prathamesh Kulkarni wrote:
Hi,
The attached patch adds special-casing for strcpy/strncpy to dse pass.
Bootstrapped+tested on x86_64-unknown-linux-gnu.
OK for GCC 8 ?
What is special on strcpy/strncpy? Unlike memcpy/memmove/memset, you don't
know the length they store (at least not in general), you don't know the
value, all you know is that they are for the first argument plain store
without remembering the pointer or anything based on it anywhere except in
the return value.
I believe stpcpy, stpncpy, strcat, strncat at least have the same behavior.
On the other side, without knowing the length of the store, you can't treat
it as killing something (ok, some calls like strcpy or stpcpy store at least
the first byte).
Well, I assumed a store to dest by strcpy (and friends), which gets
immediately freed would count
as a dead store since free would kill the whole memory block pointed
to by dest ?
Yes. But does it happen often in practice? I wouldn't mind exploring
this for gcc-8, but I'd like to see real-world code where this happens.
jeff
