Displaying 2 results from an estimated 2 matches for "rl210467".
2017 May 23
4
[poison] is select-of-select to logic+select allowed?
Hi,
Let me try to give a bit more context on why select is so tricky.
First thing to consider is which transformations we would like to support:
1) Control-flow -> select (SimplifyCFG)
if (c)
a = x
else
a = y
=>
%a = select %c, %x, %y
2) select -> control-flow; reverse of 1)
Not sure if this is done at IR level, or only later at SDAG.
3) select ->
2017 May 23
6
[poison] is select-of-select to logic+select allowed?
...known limitations/objections to the freeze instruction patches that John listed? Or are we just being cautious and/or waiting for more people to review those?
I can answer some of the DAG questions:
(a) Yes, we have nsw/nuw/exact down there. They've been around since: https://reviews.llvm.org/rL210467 .
(b) Yes, we use those bits to enable transforms, but it's not nearly as common as in IR. It's also likely that we'll drop those bits during transforms.
(c) Yes, we do all kinds of select transforms without regard for poison.
(d) AFAIK, there is no accounting for poison in the DAG f...