[mlir] Fixed memory leak after D141726.

[vzakhari]

Summary

Reported in https://lab.llvm.org/buildbot/#/builders/5/builds/30788

[vitalybuka]

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

1236

Isn't the correct way is to use .get instead if .release here?

[vzakhari]

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

1236

I just want to take control over the underlying MDTuple so that I can "wire" it as a Metadata operand, and later delete it (with the new code). FWIW, I believe the same approach is used in llvm/lib/Bitcode/Reader/MetadataLoader.cpp:BitcodeReaderMetadataList::getMetadataFwdRef.

[vitalybuka]

Please either land this one ASAP, or if you want another review, revert original, to recover bots.

[vzakhari]

I decided to merge this to unblock the sanitizer buildbot. If there are concerns about this code, I will rework it.

[vitalybuka]

In D141985#4061113, @vzakhari wrote:

I decided to merge this to unblock the sanitizer buildbot. If there are concerns about this code, I will rework it.

Thanks!

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

for (auto &op : metadata.getBody().getOps()) {
               llvm::MDNode::getTemporary(ctx, std::nullopt).release());
           operands.push_back(llvm::ConstantAsMetadata::get(
               llvm::ConstantInt::get(offsetTy, offset)));
         }
       } else if (auto tagOp = dyn_cast<LLVM::TBAATagOp>(op)) {
         // Use temporary MDNode's as the placeholders for the base and access
         // types to prevent uniquing the tag nodes until they are finalized.
         operands.push_back(
             llvm::MDNode::getTemporary(ctx, std::nullopt).release());
         operands.push_back(
             llvm::MDNode::getTemporary(ctx, std::nullopt).release());
         operands.push_back(llvm::ConstantAsMetadata::get(
             llvm::ConstantInt::get(offsetTy, tagOp.getOffset())));
         if (tagOp.getConstant())
           operands.push_back(llvm::ConstantAsMetadata::get(
               llvm::ConstantInt::get(offsetTy, 1)));
       }
for (auto &op : metadata.getBody().getOps()) {
         // is checked by module verifier.
         Operation *refDef = SymbolTable::lookupSymbolIn(metadata, refName);
         llvm::MDNode *refNode = tbaaMetadataMapping.lookup(refDef);
         if (!refNode) {
           op.emitOpError() << "llvm::MDNode missing for the member '@"
                            << refName << "'";
           return failure();
         }
+        auto *tempMD = cast<llvm::MDNode>(descNode->getOperand(opNum).get());
         descNode->replaceOperandWith(opNum, refNode);
+        // Deallocate temporary MDNode's explicitly.
+        // Note that each temporary node has a single use by creation,
+        // so it is valid to deallocate it here.
+        llvm::MDNode::deleteTemporary(tempMD);
       }
     }
   }
 
   return success();
 }
 
 llvm::Type *ModuleTranslation::convertType(Type type) {