[PATCH] D29813: [DAGCombiner] Fix DebugLoc propagation when folding !(x cc y) -> (x !cc y)

[Andrea Di Biagio via Phabricator via llvm-commits]

andreadb added inline comments.


================
Comment at: lib/CodeGen/SelectionDAG/DAGCombiner.cpp:4700-4703
+        return DAG.getSetCC(SDLoc(N0), VT, LHS, RHS, NotCC);
       case ISD::SELECT_CC:
-        return DAG.getSelectCC(SDLoc(N), LHS, RHS, N0.getOperand(2),
+        return DAG.getSelectCC(SDLoc(N0), LHS, RHS, N0.getOperand(2),
                                N0.getOperand(3), NotCC);
----------------
With this change, we always propagate the debug location of N0.

However, this may be suboptimal if we end up in a situation where N0 has a null DebugLoc, and the DebugLoc of N is not null. In that case, shouldn't we propagate SDLoc(N) instead?

When constructing a new SetCC/SelectCC node, what if we give higher priority to SDLoc(N) over SDLoc(N0) based on whether `N0->getDebugLoc()` returns a null location?

In order to guarantee a deterministic schedule, we could always call `SelectionDAG::UpdadeSDLocOnMergedSDNode()` on the newly created dag node, with the goal to set the new IROrder equal to the minimum node order between N0 and N.

Not sure if that makes sense.
I hope this helps.


https://reviews.llvm.org/D29813