Connor Abbott
b6e5a03499
The old code was both too aggressive and not aggressive enough in
inserting (jp), and it wasn't based at all on a solid understanding of
how the hardware operates. It inserted an extra unnecessary (jp) at the
beginning of an if statement right after the conditional branch, which
is unnecessary. On the other hand, the only case where it didn't
insert a (jp) was a block with one predecessor that has only one
successor. We usually don't emit these kinds of blocks, or if we do then
one of the blocks is empty, but there is a case where we *do* and the
difference actually matters: for something like
while (true) {
if (...) {
// do stuff
...
break;
}
}
The instructions inside the if could be moved below the loop, except
that they are supposed to execute before control flow is merged if the
loop trip count is nonuniform. The subgroup reduce/scan macro does
exactly this, and relies on the control flow being correct. We have to
insert a (jp) after the loop, which this code wasn't doing, breaking the
scan macro.
Since we're now using the physical edges in a non-trivial way, we have
to preserve them better when we modify control flow in ir3_legalize.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14412>
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