On 10/12/20 2:44 PM, Martin Liška wrote:
On 10/7/20 10:00 AM, Richard Biener wrote:
As said I'd have a BB-local pass over BBs recording the index variable
and the range covered by the BBs gcond, plus recording how many excess
stmts there are for eventual code motion.
Only after that BB-local pass start to group BBs in a walk from dominated to
dominating BBs looking for common indexes and building a case vector.
The main thing is to avoid repeatedly analyzing BBs conditions (so the first
pass could be also a on-demand precompute thing) and making the
case vector build optimal.
I have a patch that does that using the infrastructure from tree-ssa-reassoc.
Now I would like to implement the code hoisting. Am I right that we want
something like:
if (index == C0)
goto BB_0;
else
{
BB1_to_hoist_stmts;
if (index == C1)
goto BB_1;
else
{
BB2_to_hoist_stmts;
if (index == C2)
goto BB_2;
else
goto default_BB;
}
}
be converted into:
switch(index)
{
case C0:
goto BB_0;
case C1:
BB1_to_hoist_stmts;
goto BB_1;
case C2:
BB1_to_hoist_stmts;
BB2_to_hoist_stmts;
goto BB_2;
else:
BB1_to_hoist_stmts;
BB2_to_hoist_stmts;
goto default_BB;
}
?
Reading again Richi's comment:
ifcombine simply hoists any stmts without side-effects up the
dominator tree and thus only requires BBs without side-effects
(IIRC there's a predicate fn for that).
we likely want to hoist the statements "up" to the gswitch BB?
Martin
Thanks,
Martin
