[mlir][LLVMIR] Fix oneToOneRewrite for zero-result ops

[Mogball]

Summary

oneToOneRewrite segfaulted for zero result-ops because a null type was being
passed to the op builders.

[rriddle]

Was there any place upstream that could trigger this?

[Mogball]

Apparently not. It was only ever being used to convert ops with non-zero results.

mlir/lib/Conversion/LLVMCommon/Pattern.cpp

 
 /// Replaces the given operation "op" with a new operation of type "targetOp"
 /// and given operands.
 LogicalResult LLVM::detail::oneToOneRewrite(
     Operation *op, StringRef targetOp, ValueRange operands,
     LLVMTypeConverter &typeConverter, ConversionPatternRewriter &rewriter) {
   unsigned numResults = op->getNumResults();
 
-  Type packedType;
+  SmallVector<Type> resultTypes;
   if (numResults != 0) {
-    packedType = typeConverter.packFunctionResults(op->getResultTypes());
-    if (!packedType)
+    resultTypes.push_back(
+        typeConverter.packFunctionResults(op->getResultTypes()));
+    if (!resultTypes.back())
       return failure();
   }
 
   // Create the operation through state since we don't know its C++ type.
   Operation *newOp =
       rewriter.create(op->getLoc(), rewriter.getStringAttr(targetOp), operands,
-                      packedType, op->getAttrs());
+                      resultTypes, op->getAttrs());
 
   // If the operation produced 0 or 1 result, return them immediately.
   if (numResults == 0)
     return rewriter.eraseOp(op), success();
   if (numResults == 1)
     return rewriter.replaceOp(op, newOp->getResult(0)), success();
 
   // Otherwise, it had been converted to an operation producing a structure.