CodeGen, SelectionDAG: Increase width of NumOperands and NumValues

[majnemer]

Summary

Something like:
%a = type { [65536 x i8] }
store %a zeroinitializer, %a* undef

can generate an SDNode with more than USHRT_MAX results. In this
particular case, we will end up thinking we have zero values.

When it would come time to make an SDValue, we would assert because we
wouldn't think we had any values at all.

This fixes PR21513.

N.B. The smallest, most minimal test case I could write takes three
minutes on a very powerful machine.

[hfinkel]

Does this actually solve the problem? How about adding a better assert and then making sure that we don't combine token-factors nodes when the result would have too many operands (I'm assuming the token factor node is actually the problem)? Making the structure bigger is not something to be done lightly.

[majnemer]

We discussed this on IRC but I'll repeat the conclusion our conclusion for the benefit of all.

SelectionDAGBuilder will attempt to create a MERGE_VALUES node with more than USHRT_MAX operands in order to turn our ConstantArray into an SDNode.

It has been determined that this is a correct fix but possible a costly one as it grows the size of SDNode.

For now, I will just add assertions to SDNode's constructor to catch this a little eagerly instead of asserting later on in SDValue.

[majnemer]

Assertion added in rL221560.

[qiucf]

Is this still relevant?

include/llvm/CodeGen/SelectionDAGNodes.h

private:
   /// ValueList - The types of the values this node defines.  SDNode's may
   /// define multiple values simultaneously.
   const EVT *ValueList;
 
   /// UseList - List of uses for this SDNode.
   SDUse *UseList;
 
   /// NumOperands/NumValues - The number of entries in the Operand/Value list.
-  unsigned short NumOperands, NumValues;
+  unsigned NumOperands, NumValues;
 
   /// debugLoc - source line information.
   DebugLoc debugLoc;
 
   // The ordering of the SDNodes. It roughly corresponds to the ordering of the
   // original LLVM instructions.
   // This is used for turning off scheduling, because we'll forgo
   // the normal scheduling algorithms and output the instructions according to