Don't store nullptrs in mlir::FuncOp::getAllArgAttrs' result

[tpopp]

Summary

This method would create an ArrayRef full of nullptrs when there were no
argument attributes. This is problematic because this result could not
be passed to the FuncOp::build creator without causing a segfault.
Additionally, this is inconsistent with the the case that the argument
attribute list does not have to be the same length as the number of
arguments. Lastly, this removes error functionality that is inconsistent
with other attribute getters where only the entire return value might be
a nullptr rather than nullptrs inside a list.

[rriddle]

mlir/include/mlir/IR/FunctionSupport.h

392–394

Can we just append a range of empty dictionary instead?

481–483

I imagine this would also need to be updated.

[tpopp]

mlir/include/mlir/IR/FunctionSupport.h

392–394

Done.

[rriddle]

Was the patch updated?

[tpopp]

Store empty attributes instead of nullptrs.

[tpopp]

In D114358#3149334, @rriddle wrote:

Was the patch updated?

Whoops 🙃

[rriddle]

LGTM after resolving comments.

mlir/include/mlir/IR/FunctionSupport.h

393–394

Ah, I meant DictionaryAttr::get(getContext()). DictionaryAttr() is going to be a null attribute.

483–484

Same here.

mlir/include/mlir/IR/FunctionSupport.h

ArrayAttr getAllArgAttrs() {
     return this->getOperation()->template getAttrOfType<ArrayAttr>(
         function_like_impl::getArgDictAttrName());
   }
   /// Return all argument attributes of this function.
   void getAllArgAttrs(SmallVectorImpl<DictionaryAttr> &result) {
     if (ArrayAttr argAttrs = getAllArgAttrs()) {
       auto argAttrRange = argAttrs.template getAsRange<DictionaryAttr>();
       result.append(argAttrRange.begin(), argAttrRange.end());
     } else {
-      result.resize(getNumArguments());
+      result.append(getNumArguments(),
+                    DictionaryAttr::get(this->getOperation()->getContext()));
     }
   }
 
   /// Return the specified attribute, if present, for the argument at 'index',
   /// null otherwise.
   Attribute getArgAttr(unsigned index, StringAttr name) {
     auto argDict = getArgAttrDict(index);
     return argDict ? argDict.get(name) : nullptr;
   }
ArrayAttr getAllResultAttrs() {
     return this->getOperation()->template getAttrOfType<ArrayAttr>(
         function_like_impl::getResultDictAttrName());
   }
   /// Return all result attributes of this function.
   void getAllResultAttrs(SmallVectorImpl<DictionaryAttr> &result) {
     if (ArrayAttr argAttrs = getAllResultAttrs()) {
       auto argAttrRange = argAttrs.template getAsRange<DictionaryAttr>();
       result.append(argAttrRange.begin(), argAttrRange.end());
     } else {
-      result.resize(getNumResults());
+      result.append(getNumResults(),
+                    DictionaryAttr::get(this->getOperation()->getContext()));
     }
   }
 
   /// Return the specified attribute, if present, for the result at 'index',
   /// null otherwise.
   Attribute getResultAttr(unsigned index, StringAttr name) {
     auto argDict = getResultAttrDict(index);
     return argDict ? argDict.get(name) : nullptr;
   }