Avoid unnecessary uses of `MDNode::getTemporary`, NFC

This is a long-delayed follow-up to
5e5b85098d.

`TempMDNode` includes a bunch of machinery for RAUW, and should only be
used when necessary. RAUW wasn't being used in any of these cases... it
was just a placeholder for a self-reference.

Where the real node was using `MDNode::getDistinct`, just replace the
temporary argument with `nullptr`.

Where the real node was using `MDNode::get`, the `replaceOperandWith`
call was "promoting" the node to a distinct one implicitly due to
self-reference detection in `MDNode::handleChangedOperand`. The
`TempMDNode` was serving a purpose by delaying uniquing, but it's way
simpler to just call `MDNode::getDistinct` in the first place.

Note that using a self-reference at all in these places is a hold-over
from before `distinct` metadata existed. It was an old trick to create
distinct nodes. It would be intrusive to change, including bitcode
upgrades, etc., and it's harmless so I'm not sure there's much value in
removing it from existing schemas. After this commit it still has a tiny
memory cost (in the extra metadata operand) but no more overhead in
construction.

Differential Revision: https://reviews.llvm.org/D90079

clang/lib/CodeGen/CGLoopInfo.cpp

@@ -24,8 +24,7 @@ MDNode *
 LoopInfo::createLoopPropertiesMetadata(ArrayRef<Metadata *> LoopProperties) {
   LLVMContext &Ctx = Header->getContext();
   SmallVector<Metadata *, 4> NewLoopProperties;
-  TempMDTuple TempNode = MDNode::getTemporary(Ctx, None);
-  NewLoopProperties.push_back(TempNode.get());
+  NewLoopProperties.push_back(nullptr);
   NewLoopProperties.append(LoopProperties.begin(), LoopProperties.end());
 
   MDNode *LoopID = MDNode::getDistinct(Ctx, NewLoopProperties);
@@ -58,8 +57,7 @@ MDNode *LoopInfo::createPipeliningMetadata(const LoopAttributes &Attrs,
   }
 
   SmallVector<Metadata *, 4> Args;
-  TempMDTuple TempNode = MDNode::getTemporary(Ctx, None);
-  Args.push_back(TempNode.get());
+  Args.push_back(nullptr);
   Args.append(LoopProperties.begin(), LoopProperties.end());
 
   if (Attrs.PipelineInitiationInterval > 0) {
@@ -113,8 +111,7 @@ LoopInfo::createPartialUnrollMetadata(const LoopAttributes &Attrs,
                                               FollowupHasTransforms);
 
   SmallVector<Metadata *, 4> Args;
-  TempMDTuple TempNode = MDNode::getTemporary(Ctx, None);
-  Args.push_back(TempNode.get());
+  Args.push_back(nullptr);
   Args.append(LoopProperties.begin(), LoopProperties.end());
 
   // Setting unroll.count
@@ -176,8 +173,7 @@ LoopInfo::createUnrollAndJamMetadata(const LoopAttributes &Attrs,
                                                  FollowupHasTransforms);
 
   SmallVector<Metadata *, 4> Args;
-  TempMDTuple TempNode = MDNode::getTemporary(Ctx, None);
-  Args.push_back(TempNode.get());
+  Args.push_back(nullptr);
   Args.append(LoopProperties.begin(), LoopProperties.end());
 
   // Setting unroll_and_jam.count
@@ -250,8 +246,7 @@ LoopInfo::createLoopVectorizeMetadata(const LoopAttributes &Attrs,
                                                 FollowupHasTransforms);
 
   SmallVector<Metadata *, 4> Args;
-  TempMDTuple TempNode = MDNode::getTemporary(Ctx, None);
-  Args.push_back(TempNode.get());
+  Args.push_back(nullptr);
   Args.append(LoopProperties.begin(), LoopProperties.end());
 
   // Setting vectorize.predicate
@@ -307,7 +302,7 @@ LoopInfo::createLoopVectorizeMetadata(const LoopAttributes &Attrs,
         Ctx,
         {MDString::get(Ctx, "llvm.loop.vectorize.followup_all"), Followup}));
 
-  MDNode *LoopID = MDNode::get(Ctx, Args);
+  MDNode *LoopID = MDNode::getDistinct(Ctx, Args);
   LoopID->replaceOperandWith(0, LoopID);
   HasUserTransforms = true;
   return LoopID;
@@ -344,8 +339,7 @@ LoopInfo::createLoopDistributeMetadata(const LoopAttributes &Attrs,
       createLoopVectorizeMetadata(Attrs, LoopProperties, FollowupHasTransforms);
 
   SmallVector<Metadata *, 4> Args;
-  TempMDTuple TempNode = MDNode::getTemporary(Ctx, None);
-  Args.push_back(TempNode.get());
+  Args.push_back(nullptr);
   Args.append(LoopProperties.begin(), LoopProperties.end());
 
   Metadata *Vals[] = {MDString::get(Ctx, "llvm.loop.distribute.enable"),
@@ -359,7 +353,7 @@ LoopInfo::createLoopDistributeMetadata(const LoopAttributes &Attrs,
         Ctx,
         {MDString::get(Ctx, "llvm.loop.distribute.followup_all"), Followup}));
 
-  MDNode *LoopID = MDNode::get(Ctx, Args);
+  MDNode *LoopID = MDNode::getDistinct(Ctx, Args);
   LoopID->replaceOperandWith(0, LoopID);
   HasUserTransforms = true;
   return LoopID;
@@ -389,8 +383,7 @@ MDNode *LoopInfo::createFullUnrollMetadata(const LoopAttributes &Attrs,
   }
 
   SmallVector<Metadata *, 4> Args;
-  TempMDTuple TempNode = MDNode::getTemporary(Ctx, None);
-  Args.push_back(TempNode.get());
+  Args.push_back(nullptr);
   Args.append(LoopProperties.begin(), LoopProperties.end());
   Args.push_back(MDNode::get(Ctx, MDString::get(Ctx, "llvm.loop.unroll.full")));
 

llvm/lib/Analysis/LoopInfo.cpp

@@ -1017,8 +1017,7 @@ MDNode *llvm::makePostTransformationMetadata(LLVMContext &Context,
   SmallVector<Metadata *, 4> MDs;
 
   // Reserve first location for self reference to the LoopID metadata node.
-  TempMDTuple TempNode = MDNode::getTemporary(Context, None);
-  MDs.push_back(TempNode.get());
+  MDs.push_back(nullptr);
 
   // Remove metadata for the transformation that has been applied or that became
   // outdated.

llvm/lib/IR/MDBuilder.cpp

@@ -151,24 +151,20 @@ MDNode *MDBuilder::mergeCallbackEncodings(MDNode *ExistingCallbacks,
 }
 
 MDNode *MDBuilder::createAnonymousAARoot(StringRef Name, MDNode *Extra) {
-  // To ensure uniqueness the root node is self-referential.
-  auto Dummy = MDNode::getTemporary(Context, None);
-
-  SmallVector<Metadata *, 3> Args(1, Dummy.get());
+  SmallVector<Metadata *, 3> Args(1, nullptr);
   if (Extra)
     Args.push_back(Extra);
   if (!Name.empty())
     Args.push_back(createString(Name));
-  MDNode *Root = MDNode::get(Context, Args);
+  MDNode *Root = MDNode::getDistinct(Context, Args);
 
   // At this point we have
-  //   !0 = metadata !{}            <- dummy
-  //   !1 = metadata !{metadata !0} <- root
-  // Replace the dummy operand with the root node itself and delete the dummy.
+  //   !0 = distinct !{null} <- root
+  // Replace the reserved operand with the root node itself.
   Root->replaceOperandWith(0, Root);
 
   // We now have
-  //   !1 = metadata !{metadata !1} <- self-referential root
+  //   !0 = distinct !{!0} <- root
   return Root;
 }
 

polly/lib/CodeGen/IRBuilder.cpp

@@ -26,24 +26,22 @@ static const int MaxArraysInAliasScops = 10;
 ///
 /// The MDNode looks like this (if arg0/arg1 are not null):
 ///
-///    '!n = metadata !{metadata !n, arg0, arg1}'
+///    '!n = distinct !{!n, arg0, arg1}'
 ///
 /// @return The self referencing id metadata node.
 static MDNode *getID(LLVMContext &Ctx, Metadata *arg0 = nullptr,
                      Metadata *arg1 = nullptr) {
   MDNode *ID;
   SmallVector<Metadata *, 3> Args;
-  // Use a temporary node to safely create a unique pointer for the first arg.
-  auto TempNode = MDNode::getTemporary(Ctx, None);
   // Reserve operand 0 for loop id self reference.
-  Args.push_back(TempNode.get());
+  Args.push_back(nullptr);
 
   if (arg0)
     Args.push_back(arg0);
   if (arg1)
     Args.push_back(arg1);
 
-  ID = MDNode::get(Ctx, Args);
+  ID = MDNode::getDistinct(Ctx, Args);
   ID->replaceOperandWith(0, ID);
   return ID;
 }