On Tue, Mar 6, 2012 at 6:55 PM, Aldy Hernandez <al...@redhat.com> wrote: > On 02/29/12 03:22, Richard Guenther wrote: > >> So fixing up individual passes is easier - I can only think of PRE being >> problematic right now, I am not aware that any other pass moves loads >> or stores. So I'd simply pre-compute the stmt bit in PRE and adjust >> the >> >> if (gimple_has_volatile_ops (stmt) >> || stmt_could_throw_p (stmt)) >> continue; >> >> in compute_avail accordingly. > > > Initially I thought PRE would be problematic for transactions, but perhaps > it isn't. As I understand, for PRE we hoist loads/computations that are > mostly redundant, but will be performed on every path: > > if (flag) > a = b + c; > else > stuff; > d = b + c; <-- [b + c] always computed > > Even if we hoist [b + c] before the flag, [b + c] will be computed on every > path out of "if (flag)...". So... we can allow this transformation within > transactions, right?
Note that partial PRE (enabled at -O3) can insert expressions into paths that did _not_ execute the expression. For regular PRE you are right. Richard. > Torvald?
