Fix DRR pattern when attributes and operands are interleaved and a dag subtree appears in the rewrite

[mehdi_amini]

Summary

This fixes an incorrect fatal error in TableGen. This code probably comes
from before attributes were allowed to interleave with operands in ODS.

[jpienaar]

Thanks!

mlir/test/mlir-tblgen/rewriter-indexing.td

def test1 : Pat<(BOp $attr, (AOp $input)),
                 (BOp $attr, $input)>;
 
 // Only operand 0 and 1 should be addressed during matching.
 // CHECK: struct test2 : public ::mlir::RewritePattern {
 // CHECK: castedOp0.getODSOperands(0);
 // CHECK: castedOp0.getODSOperands(1).begin()).getDefiningOp()
 def test2 : Pat<(COp $attr1, $op1, $attr2, (AOp $op2)),
                 (BOp $attr1, $op2)>;
+
+
+// Check rewriting with a DAG subtree in the result and remapping a location.
+// CHECK: struct test3 : public ::mlir::RewritePattern {
+// CHECK: rewriter.create<test::BOp>((*a.getODSResults(0).begin()).getLoc()
+def test3 : Pat<(BOp $attr, (AOp:$a $input)),
+                (BOp $attr, (AOp $input), (location $a))>;
+

mlir/tools/mlir-tblgen/RewriterGen.cpp

std::string PatternEmitter::handleOpCreation(DagNode tree, int resultIndex,
 
   // A map to collect all nested DAG child nodes' names, with operand index as
   // the key. This includes both bound and unbound child nodes.
   ChildNodeIndexNameMap childNodeNames;
 
   // First go through all the child nodes who are nested DAG constructs to
   // create ops for them and remember the symbol names for them, so that we can
   // use the results in the current node. This happens in a recursive manner.
-  for (int i = 0, e = resultOp.getNumOperands(); i != e; ++i) {
+  for (int i = 0, e = tree.getNumArgs() - hasLocationDirective; i != e; ++i) {
     if (auto child = tree.getArgAsNestedDag(i))
       childNodeNames[i] = handleResultPattern(child, i, depth + 1);
   }
 
   // The name of the local variable holding this op.
   std::string valuePackName;
   // The symbol for holding the result of this pattern. Note that the result of
   // this pattern is not necessarily the same as the variable created by this